TECHNIQUES FOR CO2 CAPTURE USING SULFURIHYDROGENIBIUM SP. CARBONIC ANHYDRASE

Abstract

Sulfurihydrogenibium sp. carbonic anhydrase (SspCA) or mutants thereof catalyze a hydration reaction of CO.sub.2 into bicarbonate and hydrogen ions or a desorption reaction to produce a CO.sub.2 gas. Sulfurihydrogenibium sp. carbonic anhydrase (SspCA) having improved thermostability in the presence of carbonate ions as compared to in the absence of carbonate ions are useful in the capture of CO.sub.2 from a CO.sub.2-containing gas.

Claims

1. A method for capturing CO.sub.2 from a CO.sub.2-containing gas, the method comprising: contacting the CO.sub.2-containing gas with an aqueous absorption solution to dissolve the CO.sub.2 into the aqueous absorption solution, the aqueous absorption solution comprising a carbonate compound as an absorption compound; providing a recombinant Sulfurihydrogenibium sp. carbonic anhydrase (SspCA) having improved thermostability in the presence of carbonate ions as compared to in the absence of carbonate ions, to catalyze the hydration reaction of the dissolved CO.sub.2 into bicarbonate and hydrogen ions; and providing operating conditions such that the SspCA displays said improved thermostability.

2. The method of claim 1, wherein said operating conditions comprise exposing the SspCA to temperatures between 70 C. and 95 C. at some point during said method.

3. The method of claim 1, wherein said contacting is performed at a temperature between 10 C. and 90 C.; and/or the pH of the absorption solution is between 8 and 11.

4. The method of claim 1, wherein the concentration of the absorption compound in the absorption solution is between 0.1M and 5M.

5. The method of claim 1, wherein the absorption compound comprises sodium carbonate, potassium carbonate, or another carbonate salt.

6. The method of claim 1, wherein at least a portion of the SspCA provided is dissolved in the absorption solution at a concentration of 0.1 to 50 g/L.

7. The method of claim 1, wherein at least a portion of the SspCA provided is immobilized, entrapped, or otherwise attached, to particles comprised in the absorption solution, to packing material, or to other fixed structures in contact with the absorption solution.

8. The method of claim 1, wherein the SspCA is from Sulfurihydrogenibium sp. Y03A0P1 or Sulfurihydrogenibium azorense.

9. The method of claim 1, wherein the SspCA comprises one or more differences as compared to a wild-type carbonic anhydrase therefrom at residue positions corresponding to positions 18, 20, 38, 52, 57, 82, 100, 130, 150, and 181 of SEQ ID NO: 8.

10. The method of claim 9, wherein said one more amino acid differences, with respect to the amino acid residue positioning of SEQ ID NO: 8, comprise: (a) 18A, 18C, 18F, 18L, 18R, 18S, 18T, or 18W; (b) 20A, 20G, 20L, 20N, 20R, 20S, 20T, or 20W; (c) 38A, 38D, 38G, 38L, 38N, 38P, 38R, 38S, or 38W; (d) 52C, 52E, 52G, 52P, or 52T; (e) 57A, 57G, 57L, 57N, 57P, 57R, 57S, or 57V; (f) 82C or 82E; (g) 100A, 100E, 100N, 100S, 100V, or 100Y; (h) 130A, 130C, or 130L; (i) 150A, 150I, 150N, or 150S; (j) 181Q, 181L, 181M, or 181R; or (k) any combination of (a) to (j).

11. The method of claim 10, wherein said one more amino acid differences, with respect to the amino acid residue positioning of SEQ ID NO: 8, further comprise 14D, 65S, 88E, 114I, 116D, 122I, 126L, 148A, 155I, 205C, or any combination thereof.

12. The method of claim 9, wherein said one more amino acid differences, with respect to the amino acid residue positioning of SEQ ID NO: 8, comprise two or more amino acid differences which are: 18T and 20A; 18R and 20A; 2K, 181M, and 197I; 14D and 18R; 52C, 122I, 150N, and 226S; 65S and 150I; 57R and 130C; 82C and 88E; 82C and 148A; 126L and 130L; 82C and 100V; 38C, 82C, and 100V; 38G, 82C, and 100V; 38R, 82C, and 100V; 38S, 82C, and 100V; 38W, 82C, and 100V; 38S, 57A, 82C, and 100V; 38S, 57G, 82C, and 100V; 38S, 57L, 82C, and 100V; 38S, 57S, 82C, and 100V; 38S, 57V, 82C, and 100V; 18F, 20G, 38S, 57L, 82C, and 100V; 18R, 20G, 38S, 57L, 82C, and 100V; 18W, 20G, 38S, 57L, 82C, and 100V; 18R, 20W, 38S, 57L, 82C, and 100V; 18R, 20A, 38S, 57L, 82C, and 100V; 18R, 20R, 38S, 57L, 82C, and 100V; 18C, 20S, 38S, 57L, 82C, and 100V; 18C, 20V, 38S, 57L, 82C, and 100V; 18A, 20T, 38S, 57L, 82C, and 100V; or 18F, 20R, 38S, 57L, 82C, and 100V.

13. The method of claim 1, wherein the aqueous absorption solution further comprises a further absorption compound which is a primary amine, a secondary amine, a tertiary amine, a primary alkanolamine, a secondary alkanolamine, a tertiary alkanolamine, a primary amino acid, a secondary amino acid, a tertiary amino acid, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acid or a derivative thereof, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris or AHPD), N-methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine (TEA), DEA, DIPA, MMEA, TIA, TBEE, HEP, AHPD, hindered diamine (HDA), bis-(tertiarybutylaminoethoxy)-ethane (BTEE), ethoxyethoxyethanol-tertiarybutylamine (EEETB), bis-(tertiarybutylaminoethyl)ether, 1,2-bis-(tertiarybutylaminoethoxy)ethane and/or bis-(2-isopropylaminopropyl)ether, piperazine, a piperazine derivative, a piperazine or derivative thereof substituted by at least one of alkanol group, or any combination thereof.

14. A method for CO.sub.2 capture, the method comprising: in an absorption stage: contacting a CO.sub.2-containing gas with an aqueous absorption solution to dissolve the CO.sub.2 into the aqueous absorption solution, the absorption solution comprising a carbonate compound as an absorption compound; providing a recombinant Sulfurihydrogenibium sp. carbonic anhydrase (SspCA) having improved thermostability in the presence of carbonate ions as compared to in the absence of carbonate ions, in the absorption solution to catalyze the hydration reaction of the dissolved CO.sub.2 into bicarbonate and hydrogen ions, thereby producing an ion-rich solution comprising at least some of the SspCA and a CO.sub.2-depleted gas; and in a desorption stage: providing conditions for treating the ion-rich solution comprising at least some of the SspCA, so as to desorb CO.sub.2 gas from the ion-rich solution, thereby producing a regenerated absorption solution and a CO.sub.2 gas stream.

15. The method of claim 14, wherein the absorption is operated at temperatures between 20 C. and 80 C.; and the desorption is operated at temperatures between 70 C. and 110 C.

16. The method of claim 14, wherein: (a) the absorption solution has a pH of between 8 and 11; (b) the concentration of the absorption compound in the absorption solution is between 0.1 M and 5 M; (c) the absorption compound comprises sodium carbonate, potassium carbonate, or another carbonate salt; (d) at least a portion of the SspCA provided is dissolved in the absorption solution at a concentration of 0.1 to 50 g/L; (e) at least a portion of the SspCA provided is immobilized, entrapped, or otherwise attached, to particles comprised in the absorption solution, to packing material, or to other fixed structures in contact with the absorption solution; (f) the aqueous absorption solution further comprises a further absorption compound which is a primary amine, a secondary amine, a tertiary amine, a primary alkanolamine, a secondary alkanolamine, a tertiary alkanolamine, a primary amino acid, a secondary amino acid, a tertiary amino acid, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acid or a derivative thereof, monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris or AHPD), N-methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TIPA), triethanolamine (TEA), DEA, DIPA, MMEA, TIA, TBEE, HEP, AHPD, hindered diamine (HDA), bis-(tertiarybutylaminoethoxy)-ethane (BTEE), ethoxyethoxyethanol-tertiarybutylamine (EEETB), bis-(tertiarybutylaminoethyl)ether, 1,2-bis-(tertiarybutylaminoethoxy)ethane and/or bis-(2-isopropylaminopropyl)ether, piperazine, a piperazine derivative, a piperazine or derivative thereof substituted by at least one of alkanol group, or any combination thereof; or (g) any combination of (a) to (f).

17. The method of claim 14, wherein the SspCA is from Sulfurihydrogenibium sp. Y03A0P1 or Sulfurihydrogenibium azorense; and/or the SspCA comprises one or more differences as compared to a wild-type carbonic anhydrase therefrom at residue positions corresponding to positions 18, 20, 38, 52, 57, 82, 100, 130, 150, and 181 of SEQ ID NO: 8.

18. The method of claim 17, wherein said one more amino acid differences, with respect to the amino acid residue positioning of SEQ ID NO: 8, comprise: (a) 18A, 18C, 18F, 18L, 18R, 18S, 18T, or 18W; (b) 20A, 20G, 20L, 20N, 20R, 20S, 20T, or 20W; (c) 38A, 38D, 38G, 38L, 38N, 38P, 38R, 38S, or 38W; (d) 52C, 52E, 52G, 52P, or 52T; (e) 57A, 57G, 57L, 57N, 57P, 57R, 57S, or 57V; (f) 82C or 82E; (g) 100A, 100E, 100N, 100S, 100V, or 100Y; (h) 130A, 130C, or 130L; (i) 150A, 150I, 150N, or 150S; (j) 181Q, 181L, 181M, or 181R; or (k) any combination of (a) to (j).

19. The method of claim 18, wherein said one more amino acid differences, with respect to the amino acid residue positioning of SEQ ID NO: 8, further comprise 14D, 65S, 88E, 114I, 116D, 122I, 126L, 148A, 155I, 205C, or any combination thereof.

20. The method of claim 17, wherein said one more amino acid differences, with respect to the amino acid residue positioning of SEQ ID NO: 8, comprise two or more amino acid differences which are: 18T and 20A; 18R and 20A; 2K, 181M, and 197I; 14D and 18R; 52C, 122I, 150N, and 226S; 65S and 150I; 57R and 130C; 82C and 88E; 82C and 148A; 126L and 130L; 82C and 100V; 38C, 82C, and 100V; 38G, 82C, and 100V; 38R, 82C, and 100V; 38S, 82C, and 100V; 38W, 82C, and 100V; 38S, 57A, 82C, and 100V; 38S, 57G, 82C, and 100V; 38S, 57L, 82C, and 100V; 38S, 57S, 82C, and 100V; 38S, 57V, 82C, and 100V; 18F, 20G, 38S, 57L, 82C, and 100V; 18R, 20G, 38S, 57L, 82C, and 100V; 18W, 20G, 38S, 57L, 82C, and 100V; 18R, 20W, 38S, 57L, 82C, and 100V; 18R, 20A, 38S, 57L, 82C, and 100V; 18R, 20R, 38S, 57L, 82C, and 100V; 18C, 20S, 38S, 57L, 82C, and 100V; 18C, 20V, 38S, 57L, 82C, and 100V; 18A, 20T, 38S, 57L, 82C, and 100V; or 18F, 20R, 38S, 57L, 82C, and 100V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0135] FIG. 1 shows an amino acid sequence SEQ ID NO: 2 of SspCA and its nucleic acid encoding sequence SEQ ID NO: 1. The cleaved signal peptide is underscored and may be replaced with a methionine.

[0136] FIG. 2 shows sequence similarities between SspCA and the most similar proteins in GenBank, which were located by performing a protein Blast against known sequences in GenBank.

[0137] FIG. 3 is a graph of residual activity versus a one hour temperature challenge for various carbonic anhydrases including SspCA in sodium carbonate 0.3M, pH 10, at different temperatures.

[0138] FIG. 4 is a graph of residual activity versus a one hour temperature challenge for various carbonic anhydrases including SspCA in MDEA 4.2M, at pH 11.3, at different temperatures.

[0139] FIG. 5 is a process flow diagram illustrating one embodiment of the present invention, using a CO.sub.2 capture system.

[0140] FIG. 6 is another process flow diagram illustrating one embodiment of the present invention, using a CO.sub.2 capture system including a separation unit.

[0141] FIG. 7 shows a polynucleotide sequence SEQ ID NO: 7 encoding SspCA without its signal peptide. The ATG codon, encoding methionine, replaced the signal peptide encoding sequence.

[0142] FIG. 8 shows a polypeptide sequence SEQ ID NO: 8 corresponding to SspCA without its signal peptide. A methionine replaces the signal peptide.

[0143] FIG. 9 shows the polypeptide sequence SEQ ID NO: 197 of M6X Enzyme.

[0144] FIG. 10 shows a sequence alignment between SspCA (SEQ ID NO: 8) and M6X enzyme (SEQ ID NO: 197).

DETAILED DESCRIPTION

[0145] Various techniques are provided herein for CO.sub.2 capture using SspCA for catalysis, leveraging the stability and activity of the SspCA for operating conditions of the CO.sub.2 capture process.

[0146] Referring to FIG. 1, an amino acid sequence of an SspCA is illustrated. The cleaved signal peptide is underscored and may be replaced with a methionine. Various SspCA variants and functional derivatives may also be used in the CO.sub.2 capture techniques described herein. SspCA is a carbonic anhydrase that catalyzes the interconversion of CO.sub.2 and water to bicarbonate and hydrogen ions or vice versa. SspCA is obtained or derived from the thermophilic bacteria Sulfurihydrogenibium sp. Y03A0P1 (SspCA) (Russo et al. Chemical Engineering Transactions, vol. 27, 2012, p.181-186 ISSN: 1974-9791), which was first isolated in hot springs of Yellowstone park and includes the amino acid sequence as set forth in SEQ ID NO: 1 (GenBank under ACD 66216.1), belonging to the alpha class of carbonic anhydrases. Methods for isolating/obtaining an enzyme from bacteria are known, such as immunoprecipitation, ultracentrifugation or chromatographic methods. Further details and definitions related to SspCA may be found in the Definitions section below.

[0147] Referring now to FIG. 2, the listed carbonic anhydrase enzymes may also be used in CO.sub.2 capture techniques described herein. In particular, the carbonic anhydrases that are derived from thermophilic organisms may be preferably used. In addition, among the thermophiles, those that belong to the Aquificales order, such as Sulfurihydrogenobium azorense and Thermovibrio ammonificans, may be particularly preferred for certain CO.sub.2 capture techniques. The carbonic anhydrases from the Nitratiruptor genus, such as Nitratiruptor sp SB155-2, may also be preferably used.

[0148] Referring now to FIG. 5, an example of the overall CO.sub.2 capture system 10 includes a source 12 of CO.sub.2 containing gas 14. The source may be a power plant, an aluminum smelter, refinery or another type of CO.sub.2 producing operation at high or atmospheric pressure, or may also be ambient air for some specific applications such as air fractionation or air cleaning. The CO.sub.2 containing gas 14 is supplied to an absorption unit 16, which is also fed with an aqueous absorption solution 18 for contacting the CO.sub.2 containing gas 14. In some implementations, the aqueous absorption solution 18 includes carbonic anhydrase including SspCA or a functional derivative thereof and an absorption compound. The carbonic anhydrase may be free in the aqueous absorption solution 18 as dissolved enzyme or aggregates or particles of enzymes. The carbonic anhydrase may be on or in particles that are present in the aqueous absorption solution 18 and flow with it through the absorption unit 16. The carbonic anhydrase may be immobilized with respect to the particles using any method while keeping at least some of its activity. Some immobilization techniques include covalent bonding, entrapment, and so on. The carbonic anhydrase may be immobilized with respect to supports, which may be various structures such as packing material, within the absorption unit 16 so as to remain within the absorption unit 16 as the aqueous absorption solution 18 flows through it.

[0149] The CO.sub.2 containing gas 14 may be a CO.sub.2-containing effluent from various sources that includes a proportion of CO.sub.2 and other gases. For example the gas may include from about 0.03% to 60% (v/v) of CO.sub.2 although the CO.sub.2 concentration may be greater. The CO.sub.2-containing gas may also be a gas having high CO.sub.2 content up to 100%, which may be useful for the production of compounds such as sodium bicarbonate from CO.sub.2 gas as one of the starting materials.

[0150] The absorption unit 16 may be of various types, such as a packed reactor, a spray reactor, a bubble column type reactor, and so on. There may be one or more reactors that may be provided in series or in parallel. In the absorption unit 16, the SspCA catalyses the hydration reaction of CO.sub.2 into bicarbonate and hydrogen ions and thus a CO.sub.2 depleted gas 20 and an ion rich solution 22 are produced.

[0151] The ion rich solution 22 is then supplied to a desorption unit 26 to produce a CO.sub.2 stream 28 and an ion depleted solution 30. SspCA may also be present to catalyse the dehydration reaction of bicarbonate ions into CO.sub.2 and thus a CO.sub.2 depleted gas 20 and an ion lean solution 22 is produced. Alternatively, the ion rich solution 22 may be supplied to another type of regeneration step such as mineral carbonation and the like.

[0152] Referring now to FIG. 6, the system 10 may also include a separation unit 32 arranged in between the absorption unit 16 and the desorption unit 26, for removing at least some and possibly all of the SspCA in the event the enzyme is flowing with the ion rich solution 22, e.g. when the enzyme is free in solution or immobilized with respect to particles. The separation unit 32 produces an enzyme depleted stream 34 that may be supplied to the desorption unit 26 and an enzyme rich stream 36 that may be recycled, in whole or in part, to the absorption unit 16. The separation unit may also include one or more separators in series or parallel. The separators may be filters or other types of separators, depending on the removal characteristics for the enzymes and the form of the enzymes or particles.

[0153] The system may also include various other treatment units for preparing the ion rich solution for the desorption unit and/or for preparing the ion deplete unit for recycling into the absorption unit. There may be pH adjustment units or various monitoring units.

[0154] In some implementations, at least some SspCA is provided in the desorption unit. The SspCA may be provided within the input ion rich solution or added separately. The SspCA may be tailored, designed, immobilised or otherwise delivered in order to withstand the conditions in the desorption unit. SspCA may catalyze the conversion of bicarbonate ion to CO.sub.2 as described in Reaction 1 (reverse reaction).

[0155] Referring still to FIG. 6, the system may also include a measurement device 40 for monitoring properties of various streams and adjusting operation of the absorption unit 16 to achieve desired properties. Adjusting could be done by various methods including modifying the liquid and/or gas flow rates, for example, or adjusting other operating conditions.

[0156] In some implementations, the absorption unit may be operated at conditions so as to leverage the activity and/or stability of the SspCA used to catalyze the CO.sub.2 hydration reaction. For example, it has been found that SspCA can present high residual activity over a range of elevated temperatures in aqueous absorption solution including sodium carbonate or potassium carbonate. SspCA also presents high activity at lower ambient temperature to provide elevated CO.sub.2 flux in aqueous absorption solutions including sodium carbonate, potassium carbonate or MDEA. The operating conditions may include an operating temperature and at least one operating absorption compound within the absorption solution. The operating conditions may further include pH, CO.sub.2 loading, gas and liquid flow rates and compositions, and so on.

[0157] In some implementations, the operating conditions are coordinated for maximum leverage of the SspCA functionality in CO.sub.2 capture.

[0158] In some implementations, the operating conditions may include temperature conditions that, depending on various other parameters of the CO.sub.2 capture operation, may provide an absorption temperature higher than 10 C. and lower than 98 C., such as 15 C., 20 C., 25 C., 30 C., 35 C., 40 C., 45 C., 50 C., 55 C., 60 C., 65 C., 70 C., 75 C., 80 C., 85 C., 90 C., 95 C., 98 C., or any temperature in between. It should also be understood that the temperature conditions in the absorption unit may vary within a certain temperature range, since the operating temperatures at different locations within the absorption unit will be different. In addition, the temperature of the absorption solution can substantially fluctuate throughout absorption and desorption stages that can be used in some CO.sub.2 capture operations.

[0159] In some implementations, the operating conditions may include temperature conditions that, depending on various other parameters of the CO.sub.2 capture operation, may provide a desorption temperature higher than 10 C. and lower than 110 C., such as 15 C., 20 C., 25 C., 30 C., 35 C., 40 C., 45 C., 50 C., 55 C., 60 C., 65 C., 70 C., 75 C., 80 C., 85 C., 90 C., 95 C., 100 C., 105 C., 110 C. or any temperature in between. It should also be understood that the temperature conditions in the desorption unit may vary within a certain temperature range, since the operating temperatures at different locations within the desorption unit will be different. In addition, the temperature of the absorption solution can substantially fluctuate throughout absorption and desorption stages that can be used in some CO.sub.2 capture operations.

[0160] In some implementations, the operating conditions may include an aqueous absorption solution including an absorption compound, which will be further discussed below.

[0161] The enzyme is preferably used in combination with an absorption solution that will supply the CO.sub.2 carrying capacity for the process. The solution may have a composition allowing acceleration of the enzyme catalytic rate by capturing the hydrogen ion released during the hydration reaction. Using SspCA allows the CO.sub.2 capture operation to be accelerated, reducing the size of the required capture vessels and associated capital costs. In addition, by taking advantage of this accelerative mechanism, energetically favorable absorption compounds such as tertiary and hindered amines, carbonate/bicarbonate solutions and amino acids/amino acid salts can be employed to reduce associated process energy consumption, where these absorption compounds would normally be too slow to be used efficiently without enzymatic catalysis.

[0162] The aqueous absorption solution may include at least one absorption compound that aids in the absorption of CO.sub.2. The absorption compound may include potassium carbonate, sodium carbonate, ammonium carbonate, at least one amine, which may be a primary amine, a secondary amine, a tertiary amine, a primary alkanolamine, a secondary alkanolamine, a tertiary alkanolamine, and/or an amino acid with primary, secondary or tertiary amino group(s) or a combination thereof. Combinations of absorption compounds include a carbonate and at least one of the amines and/or amino acids mentioned therein or herein, to produce a promoted carbonate absorption solution.

[0163] In some scenarios, the absorption compound may be monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP), 2-(2-aminoethylamino)ethanol (AEE), 2-amino-2-hydroxymethyl-1,3-propanediol (Tris or AHPD), N-methyldiethanolamine (MDEA), dimethylmonoethanolamine (DMMEA), diethylmonoethanolamine (DEMEA), triisopropanolamine (TWA), triethanolamine (TEA), DEA, DIPA, MMEA, TIA, TBEE, HEP, AHPD, hindered diamine (HDA), bis-(tertiarybutylaminoethoxy)-ethane (BTEE), ethoxyethoxyethanol-tertiarybutylamine (EEETB), bis-(tertiarybutylaminoethyl)ether, 1,2-bis-(tertiarybutylaminoethoxy)ethane and/or bis-(2-isopropylaminopropyl)ether, and the like.

[0164] In some scenarios, the absorption compound may be piperidine, piperazine, derivatives of piperidine, piperazine which are substituted by at least one alkanol group, dialkylether of polyalkylene glycols, dialkylether or dimethylether of polyethylene glycol, amino acids comprising glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, tyrosine, tryptophan, phenylalanine, and derivatives such as taurine, N,cyclohexyl 1,3-propanediamine, N-secondary butyl glycine, N-methyl N-secondary butyl glycine, diethylglycine, dimethylglycine, sarcosine, methyl taurine, methyl--aminopropionicacid, N-(-ethoxy)taurine, N-(-aminoethyl)taurine, N-methyl alanine, 6-aminohexanoic acid, potassium or sodium salt of the amino acid or a combination thereof.

[0165] The absorption compound used to make up the aqueous absorption solution may be at least one of the example compounds, i.e. potassium carbonate, sodium carbonate and/or MDEA.

[0166] In some scenarios, the concentration of the absorption compound in the solution may be between about 0.1 M and about 10 M, depending on various factors. When the absorption compound is amine-based, the concentration of the amine-based solution may be between about 0.1M and 8M and when the absorption compound is amino acid-based, the concentration of the amino acid-based solution may be between about 0.1M and 6M.

[0167] The pH of the absorption solution may be between about 8 and about 12, depending for example on the absorption compound and on the CO.sub.2 loading of the solution.

[0168] The SspCA may be dissolved in the absorption solution. The concentration of the SspCA or functional derivative thereof may be between about 0.1 and about 50 g/L, between about 0.1 and about 10 g/L or between about 0.1 and about 5 g/L. When the SspCA is not dissolved in the solution but is rather immobilized on mobile particles or fixed packing material, the amount of immobilized SspCA may be similar so as to provide a similar activity as the therein mentioned concentrations of dissolved SspCA.

[0169] As noted above, the SspCA or functional derivative thereof may be provided free or dissolved in the solvent, immobilized or entrapped or otherwise attached to particles that are in the absorption solution or to packing material or other structures that are fixed within the reaction chamber.

[0170] In the case where the SspCA or functional derivative thereof is immobilized with respect to a support material, this may be accomplished by an immobilization technique selected from adsorption, covalent bonding, entrapment, copolymerization, cross-linking, and encapsulation, or combination thereof.

[0171] In one scenario, the SspCA or functional derivative thereof may be immobilized on a support that is in the form of particles, beads or packing. Such supports may be solid or porous with or without coating(s) on their surface. The SspCA or functional derivative thereof may be covalently attached to the support and/or the coating of the support, or entrapped inside the support or the coating. The coating may be a porous material that entraps the SspCA or functional derivative thereof within pores and/or immobilizes the SspCA by covalent bonding to the surfaces of the support. The support material may be made from a compound different than the SspCA or functional derivative thereof. The support material may include nylon, cellulose, silica, silica gel, chitosan, polyacrylamide, polyurethane, alginate, polystyrene, polymethylmetacrylate, magnetic material, sepharose, titanium dioxide, zirconium dioxide and/or alumina, respective derivatives thereof, and/or other materials. The support material may have a density between about 0.6 g/ml and about 5 g/ml such as a density above 1 g/ml, a density above 2 g/mL, a density above 3 g/mL or a density of about 4 g/mL.

[0172] In some scenarios, the SspCA or functional derivative thereof may be provided as cross-linked enzyme aggregates (CLEAs) and/or as cross-linked enzyme crystals (CLECs).

[0173] In the case of using enzymatic SspCA particles, including CLEAs or CLECs, the particles may be sized to have a diameter at or below about 17 m, optionally about 10 m, about 5 m, about 4 m, about 3 m, about 2 m, about 1 m, about 0.9 m, about 0.8 m, about 0.7 m, about 0.6 m, about 0.5 m, about 0.4 m, about 0.3 m, about 0.2 m, about 0.1 m, about 0.05 m, or about 0.025 m. The particles may also have a distribution of different sizes.

[0174] The SspCA used in connection with the techniques described herein may be an isolated and/or substantially pure form.

[0175] There is also provided a carbonic anhydrase polypeptide or functional derivatives thereof, which is stable and active at a broad range of temperatures.

[0176] In one aspect, the invention provides a carbonic anhydrase polypeptide comprising the sequence as set forth in SEQ ID NO: 2 or functional derivative thereof, an expression or cloning vector comprising a nucleotide sequence encoding such carbonic anhydrase, and a transgenic cell comprising such expression or cloning vector.

[0177] The SspCA or the derivative thereof can be used in various processes and scenarios such as those described in the following patent references that are hereby incorporated herein by reference: CA 2.291.785; CA 2.329.113, CA 2.393.016, CA 2,443,222, U.S. Pat. No. 6,908,507; EU 1 377 531, U.S. Pat. No. 7,514,056, U.S. Pat. No. 7,596,952; U.S. Pat. No. 8,066,965, U.S. Pat. No. 8,277,769, U.S. Pat. No. 6,946,288, U.S. Pat. No. 7,740,689, PCT/CA2012/050063, U.S. Ser. No. 13/503,808, U.S. Ser. No. 12/984,852, U.S. Ser. No. 13/388,854, U.S. Ser. No. 13/264,294, U.S. Ser. No. 13/388,871, U.S. Ser. No. 13/508,246, U.S. Ser. No. 11/460,402.

Definitions

[0178] In order to further appreciate some of the terms used herein, the following definitions and discussion are provided.

[0179] The expression polypeptide refers to any peptide or protein comprising two or more amino acids joined to each other by peptide bonds or modified peptide bonds. Polypeptide(s) refers to both short chains, commonly referred to as peptides, oligopeptides and oligomers, and to longer chains generally referred to as proteins. Polypeptides may contain amino acids other than the 20 gene-encoded amino acids, optionally polypeptides may contain glycine, proline, arginine, histidine, lysine, aspartic acid, glutamic acid, methionine, serine, threonine, glutamine, cysteine, asparagine, valine, leucine, isoleucine, alanine, tyrosine, tryptophan, phenylalanine, selenocysteine, selenomethionine, pyrrolysine. Polypeptide(s) include those modified either by natural processes, such as processing and other post-translational modifications, but also by chemical modification techniques. Such modifications are well described in basic texts and in more detailed monographs, as well as in a voluminous research literature and they are well known to those of skill in the art. It will be appreciated that the same type of modification may be present in the same or varying degree at several sites in a given polypeptide.

[0180] The expression functional derivative refers to a protein/peptide/polypeptide sequence that possesses a functional biological activity that is substantially similar to the biological activity of the original protein/peptide/polypeptide sequence. In other words, it refers to a polypeptide of the carbonic anhydrase as defined herein that substantially retain(s) the capacity of catalyzing the hydration of carbon dioxide. A functional derivative of the carbonic anhydrase protein/peptide as defined herein may or may not contain post-translational modifications such as covalently linked carbohydrates, if such modifications are not necessary for the performance of a specific function. The functional derivative may also comprise nucleic acid sequence variants. These variants may result from the degeneracy of the genetic code or from a mutation, substitution, addition or deletion. Further, the carbonic anhydrase as defined herein may comprise a Tag such as a histidine Tag. The term functional derivative is meant to encompass the variants, the mutants, the fragments or the chemical derivatives of a carbonic anhydrase protein/peptide. Methods for measuring carbonic anhydrase activity are known such as stirred cell reactor assay or the method described by Chirica et al. (Chirica et al. European Journal of Biochemistry, 1997, 244, 755-60). These functional derivatives have at least 60%, 65%, 70%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% 99% or 99.5% identity with the sequence as set forth in SEQ ID NO: 8, optionally over the entire length of the sequence or on a partial alignment of the sequences.

[0181] The term polynucleotide fragment, as used herein, refers to a polynucleotide whose sequence (e.g., cDNA) is an isolated portion of the subject nucleic acid constructed artificially (e.g., by chemical synthesis) or by cleaving a natural product into multiple pieces, using restriction endonucleases or mechanical shearing, or a portion of a nucleic acid synthesized by PCR, DNA polymerase or any other polymerizing technique well known in the art, or expressed in a host cell by recombinant nucleic acid technology well known to one of skill in the art.

[0182] The term polypeptide or fragments thereof as used herein refers to peptides, oligopeptides and proteins. This term also does not exclude post-expression modification of polypeptides. For example, polypeptides that include the covalent attachment of glycosyl groups, acetyl groups, lipid groups and the like are encompassed by the term polypeptide.

[0183] Techniques for determining nucleic acid and amino acid sequence identity are known in the art. Typically, such techniques include determining the nucleotide sequence of the mRNA for a gene and/or determining the amino acid sequence encoded thereby, and comparing these sequences to a second nucleotide or amino acid sequence. In general, identity refers to an exact nucleotide-to-nucleotide or amino acid-to-amino acid correspondence of two polynucleotides or polypeptide sequences, respectively. Two or more sequences (polynucleotide or amino acid) can be compared by determining their percent identity. The percent identity of two sequences, whether nucleic acid or amino acid sequences, is the number of exact matches between two aligned sequences divided by the length of the shorter sequence and multiplied by 100. An approximate alignment for nucleic acid sequences is provided by the local homology algorithm of Smith and Waterman, Advances in Applied Mathematics 2:482-489 (1981). This algorithm can be applied to amino acid sequences by using the scoring matrix developed by Dayhoff, Atlas of Protein Sequences and Structure, M. O. Dayhoff ed., 5 suppl. 3:353-358, National Biomedical Research Foundation, Washington, D.C., USA, and normalized by Gribskov, Nucl. Acids Res. 14(6):6745-6763 (1986). An exemplary implementation of this algorithm to determine percent identity of a sequence is provided by the Genetics Computer Group (Madison, Wis.) in the BestFit utility application. The default parameters for this method are described in the Wisconsin Sequence Analysis Package Program Manual, Version 8 (1995) (available from Genetics Computer Group, Madison, Wis.). Another method of establishing percent identity which can be used in the context of the present invention is the MPSRCH package of programs copyrighted by the University of Edinburgh, developed by John F. Collins and Shane S. Sturrok, and distributed by IntelliGenetics, Inc. (Mountain View, Calif.). From this suite of packages the Smith-Waterman algorithm can be employed where default parameters are used for the scoring table (for example, gap open penalty of 12, gap extension penalty of one, and a gap of six). From the data generated the Match value reflects sequence identity. Other suitable programs for calculating the percent identity between sequences are generally known in the art, for example, another alignment program is BLAST, used with default parameters. For example, BLASTN and BLASTP can be used using the following default parameters: genetic code=standard; filter=none; strand=both; cutoff=60; expect=10; Matrix BLOSUM62; Descriptions=50 sequences; sort by=HIGH SCORE; Databases=non-redundant, GenBank+EMBL+DDBJ+PDB+GenBank CDS translations+Swiss protein+Spupdate+PIR.

[0184] By substantially identical when referring to a polypeptide, it will be understood that the polypeptide of the present invention preferably has an amino acid sequence having at least about 60%, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84% 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or any other value in between to SEQ ID NO: 2 or SEQ ID NO: 8, or functional derivatives thereof, optionally over the entire length of the peptide.

[0185] One can use a program such as the CLUSTAL program to compare amino acid sequences. This program compares amino acid sequences and finds the optimal alignment by inserting spaces in either sequence as appropriate. It is possible to calculate amino acid identity or homology for an optimal alignment. A program like BLASTp will align the longest stretch of similar sequences and assign a value to the fit. It is thus possible to obtain a comparison where several regions of similarity are found, each having a different score. Both types of identity analysis are contemplated for the present invention.

[0186] With respect to protein or polypeptide, the term isolated polypeptide or isolated and purified polypeptide is sometimes used herein. This term refers primarily to a protein produced by expression of an isolated and modified polynucleotide molecule contemplated by the invention. Alternatively, this term may refer to a protein which has been sufficiently separated from other proteins with which it would naturally be associated, so as to exist in substantially pure form.

[0187] The term substantially pure refers to a preparation comprising at least 50% by weight of the carbonic anhydrase polypeptide or derivative thereof on total protein content. More preferably, the preparation comprises at least 75% by weight, and most preferably 90-99% by weight, of the carbonic anhydrase polypeptide or derivative thereof.

[0188] Purity is measured by methods appropriate for the carbonic anhydrase polypeptide or derivative thereof as described herein (e.g. chromatographic methods, agarose or polyacrylamide gel electrophoresis, HPLC analysis, and the like).

[0189] The SspCA polypeptide or functional derivative thereof may also comprise amino acids substitution such that the carbonic anhydrase or functional derivative thereof retains catalytic activity (i.e. the interconversion of CO.sub.2 with HCO.sub.3.sup. and H.sup.+). The term substituted amino acid is intended to include natural amino acids and non-natural amino acids. Non-natural amino acids include amino acid derivatives, analogues and mimetics. As used herein, a derivative of an amino acid refers to a form of the amino acid in which one or more reactive groups on the compound have been derivatized with a substituent group. As used herein an analogue of an amino acid refers to a compound that retains chemical structures of the amino acid necessary for functional activity of the amino acid yet also contains certain chemical structures that differ from the amino acid. As used herein, a mimetic of an amino acid refers to a compound in that mimics the chemical conformation of the amino acid.

[0190] As used herein, the term polynucleotide(s) generally refers to any polyribonucleotide or poly-deoxyribonucleotide, which may be unmodified RNA or DNA or modified RNA or DNA. This definition includes, without limitation, single- and double-stranded DNA, DNA that is a mixture of single- and double-stranded regions or single-, double- and triple-stranded regions, cDNA, single- and double-stranded RNA, and RNA that is a mixture of single- and double-stranded regions, hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically, double-stranded, or triple-stranded regions, or a mixture of single- and double-stranded regions. The term polynucleotide(s) also embraces short nucleotides or fragments, often referred to as oligonucleotides, that due to mutagenesis are not 100% identical but nevertheless code for the same amino acid sequence.

[0191] By substantially identical when referring to a polynucleotide, it will be understood that the polynucleotide of the invention has a nucleic acid sequence which encodes a polypeptide which is at least about 60%, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84% 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or any other value between 60 and 99.5% identical to SEQ ID NO 1 or SEQ ID NO: 8 or functional derivative thereof.

[0192] By substantially identical when referring to a polynucleotide, it will be understood that the polynucleotide of the invention has a nucleic acid sequence which is at least about 60%, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84% 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5% or any other value between 60 and 99.5% identical to SEQ ID NO 7 or functional derivative thereof.

[0193] With reference to polynucleotides of the invention, the term isolated polynucleotide is sometimes used. This term, when applied to DNA, refers to a DNA molecule that is separated from sequences with which it is immediately contiguous to (in the 5 and 3 directions) in the naturally occurring genome of the organism from which it was derived. For example, the isolated polynucleotide may comprise a DNA molecule inserted into a vector, such as a plasmid or virus vector, or integrated into the genomic DNA of a procaryote or eucaryote. An isolated polynucleotide molecule may also comprise a cDNA molecule.

[0194] As used herein, the term vector refers to a polynucleotide construct designed for transduction/transfection of one or more cell types. Vectors may be, for example, cloning vectors which are designed for isolation, propagation and replication of inserted nucleotides, expression vectors which are designed for transcription of a nucleotide sequence in a host cell, or a viral vector which is designed to result in the production of a recombinant virus or virus-like particle, or shuttle vectors, which comprise the attributes of more than one type of vector. A number of vectors suitable for stable transfection of cells and bacteria are available to the public (e.g. plasmids, adenoviruses, baculoviruses, yeast baculoviruses, plant viruses, adeno-associated viruses, retroviruses, Herpes Simplex Viruses, Alphaviruses, Lentiviruses), as are methods for constructing such cell lines. It will be understood that the present invention encompasses any type of vector comprising any of the polynucleotide molecules of the invention.

[0195] The term transgenic cell refers to a genetically engineered cell. Methods for genetically engineering a cell are known such as molecular cloning and gene targeting. These methods can include chemical-based transfection, non chemical method, particle-based method or viral method. The host cell may be any type of cell such as a transiently-transfected or stably-transfected mammalian cell line, an isolated primary cell, an insect cell, a yeast (Saccharomyces cerevisiae or Pichia pastoris), a plant cell, a microorganism, or a bacterium (such as E. coli).

[0196] The expressions naturally occurring or wild-type refer to material in the form as it occurs in nature. For example, a naturally occurring or wild-type polypeptide or polynucleotide sequence is a sequence present in an organism that is isolated from a source in nature and which has not been intentionally modified by human manipulation. The expressions Recombinant, engineered or non-naturally occurring: it do not appears in nature, it is an artificial construct. e.g., a cell, nucleic acid, or polypeptide, refers to a material that either has been modified in a manner that would not otherwise be found in nature, or is identical thereto but produced or derived from synthetic materials and/or by manipulation using recombinant techniques.

[0197] The expression Reference sequence refers to a defined sequence to which another sequence is compared. In one aspect of the invention, the reference sequence is SEQ ID NO: 2 and preferably SEQ ID NO: 8.

[0198] The expression Coding sequence refers to the nucleic acid sequence(s) that would yield the amino acid sequence of a given protein.

[0199] The expressions Amino acid, Residue, Amino acid residue refer to the specific monomer at a sequence position of a polypeptide (e.g., G82 indicates that the amino acid or residue at position 82 of SEQ ID NO: XX is a glycine (G). The amino acid may be alanine (3 letter code: ala or one letter code: A), arginine (arg or R), asparagine (asn or N), aspartic acid (asp or D), cysteine (cys or C), glutamine (gln or Q), glutamic acid (glu or E), glycine (gly or G), histidine (his or H), Isoleucine (ile or I), leucine (leu or L), lysine (lys or K), methionine (met or M), phenylalanine (phe or F), proline (pro or P), serine (ser or S), threonine (thr or T), tryptophan (trp or W), tyrosine (tyr or Y), valine (val or V)

[0200] The expression Amino acid difference refers to an amino acid at a given position in a protein sequence that is different from the one in the reference sequence. It refers to a change in the amino acid residue at a position of a polypeptide sequence relative to the amino acid residue at a corresponding position in a reference sequence. The positions of amino acid differences generally are referred to herein as Xn, where n refers to the corresponding position in the reference sequence upon which the residue difference is based. For example, a residue difference at position X82 as compared to SEQ ID NO: 8 refers to a change of the amino acid residue at the polypeptide position corresponding to position 82 of SEQ ID NO: 8. Thus, if the reference polypeptide of SEQ ID NO: 8 has a glycine at position 82, then a residue difference at position X82 as compared to SEQ ID NO: 8 an amino acid substitution of any residue other than glycine at the position of the polypeptide corresponding to position 82 of SEQ ID NO: 8. In most instances herein, the specific amino acid residue difference at a position is indicated as XnY where Xn specifies the corresponding position as described therein, and Y is the single letter identifier of the amino acid found in the engineered polypeptide (i.e., the different residue than in the reference polypeptide). In some instances, the present disclosure also provides specific amino acid differences denoted by the conventional notation AnB, where A is the single letter identifier of the residue in the reference sequence, n is the number of the residue position in the reference sequence, and B is the single letter identifier of the residue substitution in the sequence of the engineered polypeptide. For example, G82C would refer to the substitution of the amino acid residue, glycine (G) at position 82 of reference sequence with the amino acid cystein (C). In some instances, a polypeptide of the present disclosure can include one or more amino acid residue differences relative to a reference sequence, which is indicated by a list of the specified positions where changes are made relative to the reference sequence. The present disclosure includes engineered polypeptide sequences comprising one or more amino acid differences that include either/or both conservative and non-conservative amino acid substitutions.

[0201] The term Conservative amino acid substitution refers to an amino acid at a given position in a protein sequence, that is different but similar from the one in the reference sequence. The similarity can be evaluated by using the scoring matrix developed by Dayhoff, Atlas of Protein Sequences and Structure, M. O. Dayhoff ed., 5 suppl. 3:353-358, National Biomedical Research Foundation, Washington, D.C., USA.

[0202] The term Non-conservative substitution refers to an amino acid, at a given position in a protein sequence that is different and not similar from the one in the reference sequence.

[0203] The term Deletion refers to one or several amino acid(s) at a given position in a protein sequence, that is or are absent when compared to the reference sequence.

[0204] The term Insertion refers to one or several amino acid(s) at a given position in a protein sequence, that is or are in excess when compared to the reference sequence.

[0205] The term Improved enzyme property refers to a property that is better in one enzyme when compared to the reference one. It can be an increase in stability toward some denaturing agent, an increase in thermostability, an increase in solvent stability, an increase in pH stability, an increase in enzyme activity, reduced inhibition by products (e.g., bicarbonate and/or carbonate ions), improved stability in presence of the sodium cation, improved stability in presence of the potassium cation, improved solvent solubility, or a combination thereof.

[0206] The term Stability in presence of refers to the capacity of the enzyme to remain active over a period of time when in the presence of a denaturing compound. It is usually described as a percentage of remaining activity over time.

[0207] The term Thermostability refers to the capacity of the enzyme to remain active over a period of time when exposed to a given temperature. It is usually described as a percentage of remaining activity over time.

[0208] The term Solvent stability refers to the capacity of the enzyme to remain active over a period of time when exposed to a given solvent. It is usually described as a percentage of remaining activity over time.

[0209] The term pH stability refers to the capacity of the enzyme to remain active over a period of time when exposed to a given pH, such as a higher pH. It is usually described as a percentage of remaining activity over time.

[0210] The term Increased enzyme activity refers to the capacity of an enzyme to catalyze more reaction, such as hydration of CO.sub.2 and/or dehydratation of the HCO.sub.3.sup. ion, per time unit than the reference enzyme in some given conditions, such as higher Temperature, higher pH (improved pH activity profile).

[0211] By about, it is meant that the relevant value (e.g. of temperature, concentration, pH, etc.) can vary within a certain range depending on the margin of error of the method or apparatus used to evaluate such value. For instance, the margin of error of the temperature may range between 0.5 C. to 1 C., the margin of error of the pH may be 0.1 and the margin of error of the concentration may be 20%.

[0212] Various aspects of the present invention will be more readily understood by referring to the following examples. These examples are illustrative of the wide range of applicability of the present invention and are not intended to limit its scope. Modifications and variations can be made therein without departing from the spirit and scope of the invention. Although any methods and materials similar or equivalent to those described herein can be used in the practice for testing of the present invention, the preferred methods and materials are described.

[0213] The scope of the claims should not be limited by the aspects, scenarios, implementations, examples or embodiments set forth in the examples and the description, but should be given the broadest interpretation consistent with the description as a whole.

[0214] The issued patents, published patent applications, and references that are mentioned herein are hereby incorporated by reference. In the case of inconsistencies, the present disclosure will prevail.

EXAMPLES

Example 1: Materials, Methods and Producing of SspCA Having a Polypeptide Sequence Described in SEQ ID NO: 8

[0215] An SspCA enzyme was produced without the signal peptide: the first 20 amino acids were replaced by a single methionine. The first 20 amino acids (signal peptide) are underlined in FIG. 1. The enzyme was purified and characterized in a stirred cell reactor and a micro stirred cell reactor. The resulting coding nucleotide sequence is shown in FIG. 7 and the encoded SspCA amino acid sequence is shown at FIG. 8. Amino acid residue numbering will follow that of FIG. 8.

[0216] The stirred cell reactor (SCR) assay was similar to the one described in Penders N. J. M. C. et al. entitled Kinetics of absorption of carbon dioxide in aqueous MDEA solutions with carbonic anhydrase at 298K (International Journal of Greenhouse Gas Control, (2012) 9:385-392). In brief, the pressure drop in the gas phase over the absorbing solution is monitored. This CO.sub.2 pressure drop over time is translated into CO.sub.2 absorption flux.

[0217] The micro stirred cell assays were performed using 2 ml cells in the appropriate solvent under 1 atmosphere of 100% CO.sub.2 at 22 C. The pH changes were monitored using a pH indicator present in the solution and a spectrophotometer. The pH could then be correlated to an absorbed CO.sub.2 concentration using a standard curve of optical density versus CO.sub.2 loading and then a CO.sub.2 absorption flux is obtained.

[0218] Comparative tests were performed to compare the stability and activity of SspCA with other carbonic anhydrases. SspCA was compared with the following other carbonic anhydrases: [0219] (i) A thermostable variant of the human carbonic anhydrase type II (HCAII) referred to as M6X, described in U.S. Pat. No. 7,521,217 and developed by CO.sub.2 Solutions Inc. having about 34.2% identity with SEQ ID NO: 8. From scientific literature, HCAII is known as one of the fastest enzymes with a k.sub.cat/K.sub.m of about 110.sup.8 M.sup.1s.sup.1. [0220] (ii) A thermostable enzyme that is a variant of M6X developed by CO.sub.2 Solutions Inc. and referred to as CA_A; [0221] (iii) Two other thermostable beta class carbonic anhydrases referred to as CA_B and CA_C obtained from Codexis Inc. located at 200 Penobscot Drive, Redwood City, Calif.

Example 2: Activity of SspCA and M6X in Various Solvents

[0222] The activities of SspCA and various other enzymes were compared. The activity was tested in three different absorption solutions: an aqueous absorption solution including MDEA 2M, an aqueous absorption solution including sodium carbonate (Na.sub.2CO.sub.3) 0.3M pH 10 and an aqueous absorption solution including potassium carbonate (K.sub.2CO.sub.3) 1.45M pH 10. The tests were performed in a SCR reactor at 25 C. As shown in Table 1 presented below, SspCA has a higher activity (flux) than M6X in all three absorption solutions.

TABLE-US-00001 TABLE 1 Activity of SspCA and other carbonic anhydrase enzymes (0.2 g/l) in various absorption solutions Flux Enzyme Solvent mmole .Math. min.sup.1 .Math. m.sup.2 .Math. bar.sup.1 no enzyme Na Carbonates 0.3M pH = 10 65 M6x Na Carbonates 0.3M pH = 10 780 SspCA Na Carbonates 0.3M pH = 10 1420 CA_A Na Carbonates 0.3M pH = 10 945 CA_B Na Carbonates 0.3M pH = 10 1565 CA_C Na Carbonates 0.3M pH = 10 1315 no enzyme MDEA 2M 210 M6X MDEA 2M 1280 SspCA MDEA 2M 1780 CA_A MDEA 2M 1090 CA_B MDEA 2M 2210 CA_C MDEA 2M 1540 no enzyme K.sub.2CO.sub.3 1.45M pH 10 77 M6X K.sub.2CO.sub.3 1.45M pH 10 900 SspCA K.sub.2CO.sub.3 1.45M pH 10 918 CA_A K.sub.2CO.sub.3 1.45M pH 10 Not available CA_B K.sub.2CO.sub.3 1.45M pH 10 3830 CA_C K.sub.2CO.sub.3 1.45M pH 10 Not available

[0223] From these results, SspCA presents approximately 8.5 to 22 times greater activity compared to no enzyme depending on the absorption compound and conditions that were used. SspCA also presents the same or up to 2 times greater activity compared to the M6X carbonic anhydrase depending on the absorption compound and conditions that were used. From the above tests, SspCA is faster than CA_C and slower than CA_B.

Example 3: Stability of SspCA and M6X in Carbonate Buffer

[0224] The stabilities of SspCA and M6X were also compared. The stability was evaluated by exposing the enzymes to an absorption solution including sodium carbonate 0.3M at pH 10, potassium carbonate 1.45M pH 10 and/or potassium carbonate 1.45M pH 10, at 60 C. The tests were performed in a SCR reactor at 25 C. and under 100% CO.sub.2 conditions. As shown in Table 2 presented below, SspCA was more stable than M6X. In sodium carbonate, M6X was inactivated after one day whereas SspCA still had about 86% of the initial activity after six days of exposure and 65% after 14 days. The half life of those enzymes could be estimated at <1 day for M6X, 1.7 days for CA_B and 22 days for SspCA. The trend is the same in potassium carbonate.

TABLE-US-00002 TABLE 2 Stability of SspCA and M6X (0.2 g/l) in sodium or potassium carbonate at 60 C. (activity measured at 25 C.) Flux.sub.c mmole .Math. Enzyme Days Solvent min.sup.1 .Math. m.sup.2 .Math. bar.sup.1 M6X 0 Na Carbonate 0.3M pH = 10 720 M6X 1 Na Carbonate 0.3M pH = 10 0 M6X 0 K Carbonate 1.45M pH = 10 1100 M6X 1 K Carbonate 1.45M pH = 10 0 M6X 0 K Carbonate 1.45M pH = 12 1520 M6X 1 K Carbonate 1.45M pH = 12 27 SspCA 0 Na Carbonate 0.3M pH = 10 1360 SspCA 1 Na Carbonate 0.3M pH = 10 1530 SspCA 6 Na Carbonate 0.3M pH = 10 1170 SspCA 14 Na Carbonate 0.3M pH = 10 890 SspCA 0 K Carbonate 1.45M pH = 10 918 SspCA 1 K Carbonate 1.45M pH = 10 593 SspCA 3 K Carbonate 1.45M pH = 10 609 SspCA 7 K Carbonate 1.45M pH = 10 498 SspCA 0 K Carbonate 1.45M pH = 12 970 SspCA 1 K Carbonate 1.45M pH = 12 665 CA_B 0 Na Carbonate 0.3M pH = 10 1500 CA_B 1 Na Carbonate 0.3M pH = 10 840 CA_B 3 Na Carbonate 0.3M pH = 10 607 Flux.sub.c = Flux with enzyme Flux no enzyme

[0225] From these results, SspCA presents not only greater initial activity compared to M6X, but maintains elevated activity over a longer period of time and thus shows greater stability. Furthermore, SspCA presents slightly lower initial activity than CA_B but shows a greater stability.

Example 4: Residual Activities of SspCA, M6X, CA_a, CA_B and CA_C in Sodium Carbonate or MDEA Solutions

[0226] The short term stability of M6X, CA_A, CA_B, CA_B and SspCA was compared in two absorption solutions. The first aqueous absorption solution included sodium carbonate 0.3M at pH 10 and the results are illustrated in FIG. 3. The second aqueous absorption solution included MDEA 4.2M (pH 11.3) and the results are illustrated in FIG. 4. All enzymes were provided at a concentration of 0.2 g/l. The test included exposing the absorption solutions including the enzymes to different temperatures for one hour and then the residual activity was measured using micro stirred cell at 22 C.

[0227] Referring to FIG. 3, the temperature required to reduce the activity of the enzyme to 50% residual activity was 57 C. for M6X, 70 C. for CA_A, 72 C. for CA_B, 90 C. for CA_C and 95 C. for SspCA, in the sodium carbonate solution. The SspCA showed higher residual activity at all tested temperatures over the range of 55 C. to 100 C. The SspCA showed notably higher residual activity around the temperature range of 85 C. to 95 C. compared to the other enzymes.

[0228] Referring to FIG. 4, the temperature required to reduce the activity of the enzyme to 50% residual activity was 65 C. for M6X, 69 C. for SspCA, 68 C. for CA_A, 79 C. for CA_B and >85 C. for CA_C, in the MDEA solution. The SspCA is more stable than M6X (variant from human carbonic anhydrase).

Example 5: Comparison of Amino Acid Sequences Between Carbonic Anhydrase Obtained from Sulfurihydrogenibium sp. Y03A0P1 and the Most Similar Protein in GenBank

[0229] As shown at FIG. 2, the most similar carbonic anhydrase from the carbonic anhydrase obtained from Sulfurihydrogenibium sp. Y03A0P1 is from Sulfurihydrogenibium azorense Az-Fu1 with 58% identity, and the nearest one outside the Sulfurihydrogenibium genus is the one from Tolumonas auensis with 50% identity.

[0230] Based on data in Tables 1 and 2 and in FIGS. 3 and 4, SspSCA would have an enhanced impact in CO.sub.2 capture in sodium and potassium carbonate solutions because of its highest activity and stability. In a typical CO.sub.2 capture process using carbonate based solutions, the experimental data support that SspCA will transform many more CO.sub.2 molecules than the other enzymes during its lifetime in the process given its high activity level and higher stability at higher temperature. For instance, from Example 2 above, using the same conditions as in that test, we can expect that a solution with SspCA, within its lifetime, will transform 4.310.sup.7 mmole.Math.m.sup.2.Math.bar.sup.1 while one with CA_B will transform 3.710.sup.6 mmole.Math.m.sup.2.Math.bar.sup.1. This may be obtained by multiplying initial Flux (Flux at day 0) with half-life. This enhanced transformation of CO.sub.2 is significant and can allow improved efficiency and economics of CO.sub.2 capture operations. Operating conditions may thus be provided in absorption and/or desorption for leveraging the higher combined stability and activity effect of the SspCA to achieve an overall increase in biocatalytic impact.

Example 6: SspCA's Stability Improvement in Carbonate-Based Buffer

[0231] Recombinant (or engineered) carbonic anhydrase (CA) polypeptides having improved properties relative to wild-type SspCA (FIG. 8) were generated. The latter CAs are hereafter referred as improved variants or improved mutants. The improved variants were generated using directed evolution techniques that are well known by those skilled in the art.

[0232] The improved properties can be one or a combination of: improved thermostability, improved activity (hydration of CO.sub.2 and/or dehydratation of the HCO.sub.3.sup. ion), improved high pH stability (eg. pH 7 to 12), improved pH activity profile, reduced inhibition by products (eg. bicarbonate and/or carbonate ions), improved stability in presence of the sodium cation, improved stability in presence of the potassium cation, improved solvent solubility, or a combination thereof.

[0233] The improved variants comprise at least one or more amino acid substitutions in their amino acid sequence relative to that of wild-type SspCA (Seq ID No: 8) that results in CA exhibiting improved properties. An improved variant can have in its amino acid sequence 1 or more substitutions, 2 or more substitutions, 3 or more substitutions, 4 or more substitutions, 5 or more substitutions, 6 or more substitutions, 7 or more substitutions, 8 or more substitutions, 9 or more substitutions, 10 or more substitutions. The improved variant may additionally comprise neutral mutations. The improved variant can be substantially identical to SspCA. By substantially identical the sequence of the invention has an amino acid sequence which is at least about 60%, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84% 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 99.5% identical to SEQ ID NO 8. The substitutions comprise but are not limited to any mutations at positions listed in Tables 5, 6 and 9 or any functional derivative thereof. The mutation can be conservative or non-conservative. Non-limiting examples of conservative mutations are given in Table 3. Conservative mutations are known to usually provide similar effect to protein structure and function. The functional derivative can comprise substitution, insertion and/or deletion, or combination thereof. The variant can be free or immobilized.

TABLE-US-00003 TABLE 3 Possible conservative mutations Conservative Class Amino acid mutation class Non-polar A, V, L, I Non-polar Other non-polar Other non-polar G, M Non-polar Aromatic H, F, Y, W Aromatic Polar Q, N, S, T Polar > acidic, basic Acidic D, E Acidic > polar Basic K, R Basic > polar Other C, P None

[0234] The functional derivative can have any substitution at surface-exposed residues. It is known by those skilled in the art that most neutral substitutions, i.e. mutations that retain biological and biophysical properties of a given protein, are found at these positions. Mutations tend also to be found at residue not involved in the function of the protein and away from the active site region. Table 4 describes the location and features of every SspCA residue in its 3D-structure (PDB ID 4G7A).

TABLE-US-00004 TABLE 4 Features of each Ssp-CA residue Position Structural location/feature X1 Surface exposed X2 Surface exposed X3 Surface exposed X4 Surface exposed X5 Surface exposed X6 Surface exposed X7 Surface exposed X8 Surface exposed X9 Surface exposed X10 Surface exposed X11 Surface exposed X12 Surface exposed X13 Surface exposed X14 Surface exposed X15 Surface exposed X16 Buried X17 Surface exposed X18 Surface exposed X19 Surface exposed X20 Surface exposed X21 Surface exposed X22 Surface exposed X23 Surface exposed X24 Surface exposed X25 Surface exposed X26 Buried, disulfide bridge X27 Surface exposed X28 Surface exposed X29 Surface exposed X30 Surface exposed X31 Surface exposed X32 Buried X33 Surface exposed X34 Surface exposed X35 Surface exposed X36 Buried X37 Surface exposed X38 Surface exposed X39 Surface exposed X40 Surface exposed X41 Surface exposed X42 Surface exposed X43 Surface exposed X44 Surface exposed X45 Surface exposed X46 Surface exposed X47 Surface exposed X48 Surface exposed X49 Surface exposed X50 Surface exposed X51 Surface exposed X52 Surface exposed X53 Surface exposed X54 Surface exposed X55 Surface exposed X56 Buried X57 Surface exposed X58 Surface exposed X59 Buried X60 Surface exposed X61 Buried X62 Surface exposed X63 Surface exposed X64 Surface exposed X65 Surface exposed X66 Surface exposed, proton shuttle X67 Surface exposed X68 Buried X69 Surface exposed X70 Buried X71 Surface exposed X72 Surface exposed X73 Surface exposed X74 Surface exposed X75 Surface exposed X76 Surface exposed X77 Surface exposed X78 Buried X79 Surface exposed X80 Surface exposed X81 Surface exposed X82 Surface exposed X83 Surface exposed X84 Surface exposed X85 Surface exposed X86 Surface exposed X87 Surface exposed X88 Surface exposed X89 Surface exposed X90 Buried X91 Buried, metal coordinating X92 Buried X93 Buried, metal coordinating X94 Surface exposed X95 Surface exposed X96 Surface exposed X97 Surface exposed X98 Buried X99 Surface exposed X100 Surface exposed X101 Surface exposed X102 Surface exposed X103 Surface exposed X104 Surface exposed X105 Surface exposed X106 Surface exposed X107 Buried X108 Buried X109 Buried X110 Buried, metal coordinating X111 Buried X112 Surface exposed, active site pocket X113 Buried X114 Surface exposed X115 Surface exposed X116 Surface exposed X117 Surface exposed X118 Surface exposed X119 Surface exposed X120 Surface exposed X121 Buried X122 active site pocket, inner sphere X123 Buried X124 Buried X125 Buried X126 Buried X127 Buried X128 Surface exposed X129 Surface exposed X130 Surface exposed X131 Surface exposed X132 Surface exposed X133 Surface exposed X134 Surface exposed X135 Surface exposed X136 Buried X137 Surface exposed X138 Surface exposed X139 Buried X140 Surface exposed X141 Surface exposed X142 Surface exposed X143 Surface exposed X144 Surface exposed X145 Surface exposed X146 Surface exposed X147 Surface exposed X148 Surface exposed X149 Surface exposed X150 Surface exposed X151 Surface exposed X152 Surface exposed X153 Surface exposed X154 Surface exposed X155 Surface exposed X156 Surface exposed X157 Surface exposed X158 Surface exposed X159 Surface exposed X160 Surface exposed X161 Buried X162 Surface exposed X163 Surface exposed X164 Surface exposed X165 Surface exposed X166 Surface exposed X167 Surface exposed X168 Surface exposed X169 Surface exposed X170 Surface exposed X171 Surface exposed X172 Surface exposed X173 Surface exposed X174 Buried, active site pocket X175 Surface exposed, active site pocket X176 Surface exposed, active site pocket X177 Surface exposed, active site pocket X178 Surface exposed, active site pocket X179 Surface exposed X180 Surface exposed, disulfide bridge X181 Surface exposed X182 Surface exposed X183 Surface exposed X184 Surface exposed X185 Surface exposed X186 Buried, active site pocket X187 Buried X188 Buried X189 Buried X190 Surface exposed X191 Surface exposed X192 Surface exposed X193 Surface exposed X194 Surface exposed X195 Buried X196 Surface exposed X197 Surface exposed X198 Surface exposed X199 Surface exposed X200 Surface exposed X201 Surface exposed X202 Surface exposed X203 Buried X204 Surface exposed X205 Surface exposed X206 Surface exposed X207 Surface exposed X208 Surface exposed X209 Surface exposed X210 Buried X211 Surface exposed X212 Surface exposed X213 Surface exposed X214 Surface exposed X215 Surface exposed X216 Surface exposed X217 Surface exposed X218 Surface exposed X219 Surface exposed X220 Surface exposed X221 Surface exposed X222 Surface exposed X223 Buried X224 Surface exposed X225 Surface exposed X226 Surface exposed X227 Surface exposed

[0235] Following tables 5 and 6 describe the mutations highlighted by the directed evolution works presented herein. To the knowledge of the inventors, none of these mutations were published previously. All of these mutations occur at SspCA surface and they are well distributed. Some mutations are conservative while others are not.

[0236] Table 5 provides a description of the amino acid substitutions as reflected in SEQ ID NO, together with the observed activity of the mutated enzyme after 15 min at 92 C. The stability was evaluated by comparison of the residual activity signal level after a 15 min exposure in 0.3M Na.sub.2CO.sub.3/NaHCO.sub.3 pH 10.

[0237] The legend for Tables 5 and 6 is: [0238] =Residual activity level about that of wild-type SspCA [0239] +=Residual activity level of about 100% to 200% that of wild-type SspCA [0240] ++=Residual activity level of about 200% to 400% that of wild-type SspCA [0241] +++=Residual activity level of about 400% to 800% that of wild-type SspCA [0242] ++++=Residual activity level of about 800% to 1600% that of wild-type SspCA [0243] NT=Not tested

TABLE-US-00005 TABLE 5 Variants exhibiting improved stability following a 15 min exposure at 92 C. in 0.3M Na.sub.2CO.sub.3/NaHCO.sub.3 pH 10 Activity after Seq ID 15 min NO Amino acid 92 C. (nt/aa) substitution Challenge.sup. 9/10 Q18A + 15/16 Q18L + 17/18 Q18R + 19/20 Q18S + 23/24 K20A + 25/26 K20G + 27/28 K20L + 29/30 K20N + 31/32 K20R + 35/36 K20T + 37/38 K38A + 41/42 K38D + 43/44 K38G + 45/46 K38L + 47/48 K38N + 49/50 K38P + 51/52 K38R + 57/58 Y52C + 59/60 Y52E + 61/62 Y52G + 63/64 Y52P + 65/66 Y52T + 69/70 K57G + 73/74 K57N + 75/76 K57P + 77/78 K57R + 79/80 K57S + 81/82 K57V + 83/84 G82C ++ 85/86 G82E + 87/88 I100A + 89/90 I100E + 91/92 I100N + 93/94 I100S + 97/98 I100Y + 99/100 E116D + 101/102 G130A + 103/104 G130C + 105/106 G130L + 107/108 K150A + 109/110 K150S + 111/112 N155I + 113/114 T181L + 115/116 T181Q + 117/118 T181R + 119/120 S205C + 121/122 Q18T-K20A + 123/124 Q18R-K20A + 125/126 E2K; T181M; K197I + 127/128 E14D; Q18R + 129/130 Y52C; V122I; + K150N; G226S 131/132 G65S; K150I + 133/134 K57R; G130C + 135/136 G82C; K88E + 137/138 G82C; G148A + 139/140 M126L; G130L + 141/142 G82C; I100V ++ 143/144 K38C; G82C; I100V +++ 145/146 K38G; G82C; I100V +++ 147/148 K38R; G82C; I100V +++ 149/150 K38S; G82C; I100V +++ 151/152 K38W; G82C; I100V +++ 153/154 K38S; K57A; G82C; ++++ I100V 155/156 K38S; K57G; G82C; ++++ I100V 157/158 K38S; K57L; G82C; ++++ I100V 159/160 K38S; K57S; G82C; ++++ I100V 161/162 K38S; K57V; G82C; ++++ I100V; 163/164 Q18F; K20G; K38S; +++++ K57L; G82C; I100V 165/166 Q18R; K20G; K38S; +++++ K57L; G82C; I100V 167/168 Q18W; K20G; K38S; +++++ K57L; G82C; I100V 169/170 Q18R; K20W; K38S; +++++ K57L; G82C; I100V 171/172 Q18R; K20A; K38S; +++++ K57L; G82C; I100V 173/174 Q18R; K20R; K38S; +++++ K57L; G82C; I100V 175/176 Q18C; K20S; K38S; +++++ K57L; G82C; I100V 177/178 Q18C; K20V; K38S; +++++ K57L; G82C; I100V 179/180 Q18A; K20T; K38S; +++++ K57L; G82C; I100V 195/196 Q18F; K20R; K38S; +++++ K57L; G82C; I100V .sup.Stability evaluated by comparison of the residual activity signal level after a 15 min exposure in 0.3M Na.sub.2CO.sub.3/NaHCO.sub.3 pH 10.

TABLE-US-00006 TABLE 6 Residual activity levels of SSp-CA variants challenged under various conditions Assay 1 Assay 2 Assay 3 Seq ID Amino acid 0.3M Na.sub.2CO.sub.3 pH 10 0.3M Na.sub.2CO.sub.3 pH 10 0.3M Na.sub.2CO.sub.3 pH 10 (nt/aa) substitution 85 C. 16 h 96 C. 1 h 98 C. 1 h 193/194 E14D NT NT 15/16 Q18L + + NT 17/18 Q18R + + NT 29/30 K20N + + NT 35/36 K20T + + NT 47/48 K38N + + NT 57/58 Y52C + NT 73/74 K57N + + NT 181/182 G65S NT NT 83/84 G82C ++ ++ + 93/94 I100S NT + NT 185/186 K114I NT NT 99/100 E116D NT NT 189/190 V122I NT NT 103/104 G130C NT + NT 193/194 G148A NT NT 107/108 K150A NT NT 1019/110 K150S NT NT 111/112 N155I NT NT 113/114 T181L NT NT 115/116 T181Q NT NT 117/118 T181R NT + NT 119/120 S205C NT NT 141/142 G82C; I100V ++ ++ ++ 143/144 K38C; G82C; I100V ++ NT +++ 145/146 K38G; G82C; I100V ++ NT +++ 147/148 K38R; G82C; + NT ++ I100V; 149/150 K38S; G82C; 1100V +++ NT +++ 151/152 K38W; G82C; +++ NT +++ I100V 153/154 K38S; K57A; G82C; ++ NT NT +++ I100V; 155/156 K38S; K57G; G82C; NT NT +++ I100V 157/158 K38S; K57L; G82C; NT NT +++ I100V 159/160 K38S; K57S; G82C; NT NT +++ I100V; 161/162 K38S; K57V; G82C; NT NT +++ I100V 195/196 Q18F; K20R; K38S; ++++ NT ++++ K57L; G82C; I100V 167/168 Q18W; K20G; +++ NT +++ K38S; K57L; G82C; I100V 165/166 Q18R; K20G; K38S; +++ NT +++ K57L; G82C; I100V 169/170 Q18R; K20W; +++ NT +++ K38S; K57L; G82C; I100V 171/172 Q18R; K20A; K38S; +++ NT +++ K57L; G82C; I100V 173/174 Q18R; K20R; K38S; +++ NT +++ K57L; G82C; I100V Legend: = Residual activity about that of wild-type SspCA + = Residual activity about 100% to 200% that of wild-type SspCA ++ = Residual activity about 200% to 400% that of wild-type SspCA +++ = Residual activity about 400% to 800% that of wild-type SspCA ++++ = Residual activity about 800% to 1600% that of wild-type SspCA NT = Not tested

TABLE-US-00007 TABLE 7 Neutral mutations highlighted along the screening process with SEQ ID indicated SEQ ID Position on SEQ Naturally occurring DNA/PROT ID No: 8 amino acid Neutral mutation 193/194 14 Glu Asp 181/182 65 Gly Ser 183/184 88 Lys Glu 185/186 114 Lys Ile 99/100 116 Glu Asp 187/188 122 Val Ile 189/190 126 Met Leu 191/192 148 Gly Ala 111/112 155 Asn Ile 119/120 205 Ser Cys

TABLE-US-00008 TABLE8 Neutralpeptideinsertions Positionpairbetween whichinsertionoccurs onSEQIDNO:8 Insertion 12-13 LSTGRCWCRSSTWCKLKG 12-13 PEHWAGLLPEFFWCKEKG 53-54 KLNLH 151-152 PPAEEAKT

[0244] Table 9 provides the construction of the mutants.

TABLE-US-00009 TABLE 9 Mutants DNA and Polypeptide SEQ ID. Mutant Description SEQ ID NO (DNA) SEQ ID NO (Polypeptide) Q18A 9 10 Q18C 11 12 Q18F 13 14 Q18L 15 16 Q18R 17 18 Q18S 19 20 Q18W 21 22 K20A 23 24 K20G 25 26 K20L 27 28 K20N 29 30 K20R 31 32 K20S 33 34 K20T 35 36 K38A 37 38 K38C 39 40 K38D 41 42 K38G 43 44 K38L 45 46 K38N 47 48 K38P 49 50 K38R 51 52 K38S 53 54 K38W 55 56 Y52C 57 58 Y52E 59 60 Y52G 61 62 Y52P 63 64 Y52T 65 66 K57A 67 68 K57G 69 70 K57L 71 72 K57N 73 74 K57P 75 76 K57R 77 78 K57S 79 80 K57V 81 82 G82C 83 84 G82E 85 86 I100A 87 88 I100E 89 90 I100N 91 92 I100S 93 94 I100V 95 96 I100Y 97 98 E116D 99 100 G130A 101 102 G130C 103 104 G130L 105 106 K150A 107 108 K150S 109 110 N155I 111 112 T181L 113 114 T181Q 115 116 T181R 117 118 S205C 119 120 Q18T-K20A 121 122 Q18R-K20A 123 124 E2K-T181M-K197I 125 126 E14D-Q18R 127 128 Y52C-V122I-K150N- 129 130 G226S G65S-K150I 131 132 K57R-G130C 133 134 G82C-K88E 135 136 G82C-G148A 137 138 M126L-G130L 139 140 G82C-I100V 141 142 K38C-G82C-I100V 143 144 K38G-G82C-I100V 145 146 K38R-G82C-I100V 147 148 K38S-G82C-I100V 149 150 K38W-G82C-I100V 151 152 K38S-K57A-G82C- 153 154 I100V K38S-K57G-G82C- 155 156 I100V K38S-K57L-G82C- 157 158 I100V K38S-K57S-G82C- 159 160 I100V K38S-K57V-G82C- 161 162 I100V Q18F-K20G-K38S- 163 164 K57L-G82C-I100V Q18R-K20G-K38S- 165 166 K57L-G82C-I100V Q18W-K20G-K38S- 167 168 K57L-G82C-I100V Q18R-K20W-K38S- 169 170 K57L-G82C-I100V Q18R-K20A-K38S- 171 172 K57L-G82C-I100V Q18R-K20R-K38S- 173 174 K57L-G82C-I100V Q18C-K20S-K38S- 175 176 K57L-G82C-I100V Q18C-K20V-K38S- 177 178 K57L-G82C-I100V Q18A-K20T-K38S- 179 180 K57L-G82C-I100V G65S 181 182 K88E 183 184 K114I 185 186 V122I 187 188 M126L 189 190 G148A 191 192 E14D 193 194 Q18F-K20R-K38S- 195 196 K57L-G82C-I100V Q18T 199 200 K20W 201 202 K150I 203 204 K150N 205 206 T181M 207 208