Ultra-stable protein ionic liquids

Abstract

A method of forming a stable protein complex comprising: providing aqueous protein complexes, wherein the protein complexes are one or more of photosystem I complex from spinach, photosystem II complex from spinach, chlorophyll antennae, thylakoids, bacteriochlorophylls, chlorosomes, and photosystems from green algae, cyanobacteria, and plants; cationizing the aqueous protein complexes by the addition of stoichiometric amounts of a crosslinker in the presence of a coupling reagent; titrating the cationized protein complexes with a counter anionic polymer until the protein cation/anion pair solution becomes negative by zeta potential measurement, to create at least one antibody cation/anion pair in aqueous solution. The protein complexes cation/anion pair solution may be lyophilized to remove all of the water, forming a lyophilized solid. The lyophilized solid may be heated until a protein complex ionic liquid is generated. The cationized protein complexes may be purified from excess coupling reagents by dialysis in water.

Claims

1. A water-free ultra-stable ionic liquid comprising: one or more spinach photosystem II protein complexes cation/anion pair, wherein the protein complexes are cationized by the addition of stoichiometric amounts of one of N,N-dimethyl-1,3-propanediamine in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) coupling reagent, succinimidyl iodoacetate (SIA) in the presence of 2-(dimethylamino) ethanethiol, and N-(p-maleimidophenyl) isocyanate (PMPI) in the presence of 2-(dimethylamino) ethanethiol, and an anionic polymer consisting of (poly)ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether (C.sub.9H.sub.19C.sub.6H.sub.4—(OCH.sub.2CH.sub.2).sub.20O(CH.sub.2).sub.3SO.sub.3).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention. The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) FIG. 1 depicts a general approach to modify any protein or antibody into a stable protein or antibody, according to an embodiment of the present invention.

(3) FIG. 2 depicts a more-detailed approach to modify any protein or antibody into a stable protein or antibody, according to an embodiment of the present invention.

(4) FIG. 3 depicts a typical protein or antibody that has been cationized, according to the present invention.

(5) FIG. 4 depicts the cationization of a protein or antibody solution in the presence of a coupling agent, according to an embodiment of the present invention.

(6) FIGS. 5A-5B depict the selective cationization of IgG in the presence of coupling agents, according to an embodiment of the present invention.

(7) FIG. 6 depicts the antigen binding of an aqueous antibody at room temperature and at 100° C., according to an embodiment of the present invention.

(8) FIG. 7 depicts the antigen binding of an ionic liquid antibody at room temperature and at 200° C., according to an embodiment of the present invention.

(9) FIG. 8 depicts the stability of photosystem II protein complexes before and after ionic liquid formation.

(10) It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the sequence of operations as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration.

DETAILED DESCRIPTION OF THE INVENTION

(11) The following examples illustrate particular properties and advantages of some of the embodiments of the present invention. Furthermore, these are examples of reduction to practice of the present invention and confirmation that the principles described in the present invention are therefore valid but should not be construed as in any way limiting the scope of the invention.

(12) This invention exploits the physical properties of ionic liquids and the biological recognition of antigen-specific antibodies to create a stable and heat-resistant antibody protein ionic liquid that exhibits refrigeration-free storage and handling, which makes it suitable for use or storage at typical room temperatures. However, such a process has numerous obstacles to overcome because antibodies and many other proteins are negatively charged. This makes such proteins and antibodies difficult to ionically combine with anions. In order to create an ionic liquid with antibodies, the antibodies' charge must be made more positive. Antibodies have a great number of negative sites (e.g. carboxyl groups, —COOH; amine groups —NH.sub.2; hydroxyl groups, —OH) to address, but in order to maintain the activity of the antibody the cationization process should not be too aggressive. In short, too few positive charges yields an antibody that does not function correctly as a salt. Too many positive charges yields an antibody with diminished biological activity, i.e. once the antibody's non-acid (general) amino acids are coupled the antibody loses its specificity and its usefulness.

(13) FIG. 1 depicts a general approach 10 to modify any antibody, e.g. a native antibody. In one embodiment, four solutions may be required to produce an antibody ionic liquid: a solution of antibodies 12, a solution of cationic crosslinker molecules 14, a solution of coupling agents 16, and a corresponding anion 18. The anion 18 may be biologically-derived or abiotic. The examples presented herein utilize biologically-derived anions, but abiotic anions may be used in the same manner. After the antibodies 12 are cationized (cationized antibodies 20 with cationic crosslinker molecules depicted as “+”), biologically-derived (or biologically-compatible) anions 18 are combined with the cationized antibodies 20 to form an antibody/anion salt 22. Removal of all or most of the water, i.e. at least 95% or at least 99%, results in an ultra-stable antibody ionic liquid 24, which is depicted in a sample tube. The antibody ionic liquid 24 may require no refrigeration, may be stable (i.e. retains efficacy and functionality) at room temperature, and may be stable up to about 200° C.

(14) FIG. 2 depicts another embodiment of the invention to modify any antibody. Some of the numerous acidic sites, i.e., —COOH (carboxyl), basic sites —NH.sub.2 (amine), and neutral sites —OH (hydroxyl) are depicted on a native (unmodified) antibody 30. At least some of the carboxyl, amine and hydroxyl groups may be modified in order to achieve a cationic antibody 32, i.e. the carboxyl, amine and hydroxyl groups (depicted on native antibody 30) of the native antibody 30 are negative sites which tend to make the native antibody 30 generally anionic. This may be done selectively. Various cations may be used to selectively modify the carboxyl, amine and hydroxyl groups. For example, EDC (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide) may be used to modify the carboxyl groups, SIA (succinimidyl iodoacetate) may be used to modify the amine groups, and PMPI (N-(p-maleimidophenyl) isocyanate) may be used to modify the hydroxyl groups (not shown) to form an antibody cation 32. Cations in FIG. 2 are represented by “+”. If only a fraction of each carboxyl, amine and hydroxyl group is desired to be modified, in order to maintain the functionality of the antibody salt, the stoichiometry may be adjusted to limit the reagents (e.g., EDC, SIA, PMPI) and thereby limit the number of groups, i.e. the carboxyl, amine and hydroxyl groups, which are modified. After the antibody is cationized 32, the cationized antibody 32 may be combined with an anion 34 in order to form an antibody ionic liquid 36 after removal of most or all of the water. The antibody ionic liquid 36 is depicted in a sample tube 38.

(15) FIG. 3 depicts a typical antibody 50 (e.g. anti-hemoglobin antibodies, anti-horse spleen ferritin IgG antibodies, or blood-typing IgM Anti-A antibodies, single-chain antibodies from camelids, monoclonal Anti-Flag antibodies, monoclonal Anti-HRP2 to Plasmodium falciparum, polyclonal Anti-neuropeptide Y, and polyclonal Anti-human troponin) that has been cationized. A typical antibody 50 has a constant region 52 and a variable region 54. The constant region 52 (corresponding to about the lower two-thirds of the depicted antibody 50) is generally the same for antibodies. The variable region 54, depicted as the upper ends of the Y branches, includes an antibody epitope 56 which will be distinct for each different type of antibody, depending on its affinity for a specific antigen. This gives the antigen its functionality. In one embodiment, only the constant region 52 is modified so as to retain the functionality of the antigen 50. Even with fewer than only about 5-15% of the amino acids in the constant region 52 modified taking into account the total number of amino acids in the constant region, or about 60-90% of the negative sites in the constant region, the resulting antibody ionic liquid will exhibit binding affinity and functionality with appropriate antigens.

(16) FIG. 4 depicts the cationization of an antibody solution with a crosslinker (e.g. N,N-dimethyl-1,3-propanediamine, 2-(dimethylamino) ethanethiol, 4-(Dimethylamino)cinnamaldehyde or 3-(Dimethylamino)propionic acid hydrochloride or 5-(Dimethylamino)amylamine and 4-(Dimethylamino)-2-butenoic acid hydrochloride) in the presence of a coupling agent (e.g. 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC), succinimidyl iodoacetate (SIA), N-(p-maleimidophenyl) isocyanate (PMPI), N-α-maleimidoacet-oxysuccinimide ester (AMAS), N-β-maleimidopropyl-oxysuccinimide (BMPS), succinimidy 3-(bromoacetamido) propionate (SBAP), N-5-azido-2-nitrobenzoylsuccinimide (ANB-NOS), sulfosuccinimidyl-4,4′-azipentanoate (sulfo-SDA), and N-β-maleimidopropionic acid hydrazide (BMPH)) in the presence of a coupling agent. In one embodiment, cationization gives the antibody a positive charge without neutralizing its functionality. Too few positive charges means the antibody will not form an ionic liquid with an anion. Too many positive charges may result in the antibody losing its functionality. This balance is determined empirically. We start with a highly cationized antibody and determine any changes in binding activity. If binding activity is affected, we add fewer positive charges. FIG. 4 graphically illustrates how the concentrations of the coupling agents may affect the overall charge of the antibodies, and accordingly, about how many anions will be bound with the cationic antibodies. There are about 144 acidic amino acids on a typical antibody, and about 1600 total (acidic and non-acidic) amino acids. The non-acidic amino acids control the functionality of the antibodies. If too many (more than about 30% of the total amino acids) non-acid amino acids are coupled the antibody loses its specificity and affinity, i.e. it no longer functions as an antibody. The chart of FIG. 4 illustrates that there is a practical limit as to how many anions may be bound by a cationic antibody. The dashed line (line 63 with square data points) illustrates a cationic antibody solution that has been cationized at about 10 equivalents (theoretic—about 10 positive charges per IgG antibody) based on the strength of the coupling agents. Line 63 starts with a negative zeta potential, which indicates that the cationization was insufficient to give the antibodies a positive charge overall. Thus this low level of cationization is insufficient for use in making an antibody ionic liquid.

(17) Line 62 (solid line with circle data points) illustrates a cationic antibody solution that has been cationized at about 100 equivalents (theoretic) based on the strength of the coupling agents. Line 62 starts with a positive zeta potential, which indicates that the cationization was sufficient to give the antibodies a positive charge overall. Thus this level of cationization is sufficient for use in making an antibody ionic liquid. Likewise, line 61 (solid line with triangle data points) illustrates a cationic antibody solution that has been cationized at about 1000 equivalents (theoretic) based on the strength of the coupling agents. Line 61 starts with a positive zeta potential, which indicates that the cationization was sufficient to give the antibodies a positive charge overall. Thus this level of cationization is also sufficient for use in making an antibody ionic liquid. However, the extra strength of the coupling agents did not affect the formation of the ionic liquid to the degree expected from the concentration of the coupling agents.

(18) FIG. 5A depicts another embodiment of the invention with the selective cationization of immunoglobulin (IgG) in the presence of coupling agents. There are different numbers of the carboxyl, amine and hydroxyl groups in a typical antibody. These may be selectively coupled through the use of particular coupling agents, including, for example, SIA, PMPI, AMAS (N-α-maleimidoacet-oxysuccinimide ester), BMPS (N-β-maleimidopropyl-oxysuccinimide), SBAP (succinimidy 3-(bromoacetamido) propionate), a photoactive coupling agent (e.g. ANB-NOS (N-5-azido-2-nitrobenzoylsuccinimide) or sulfo-SDA (sulfosuccinimidyl-4,4′-azipentanoate)), or BMPH (N-β-maleimidopropionic acid hydrazide), and combinations thereof. AMAS, BMPS or SBAP may be used as a substitute for SIA. For example, SIA may be used to cationize the amine (—NH.sub.2) sites, and PMPI may be used to cationize the hydroxyl (—OH) groups. Selective cationization of these groups in the antibodies may be accomplished with selected coupling agents, and/or the use of selected coupling agents as limited reagents, in order to achieve a desired cationic state or positive zeta potential. Line 71 (line with square data points) corresponds to the cationization of carboxyl (—COOH) groups, line 72 (line with circular data points) corresponds to the cationization of amine (—NH) groups), and line 73 (line with triangular data points) corresponds to the cationization of hydroxyl (—OH) groups). In one embodiment of the present invention, each of these groups may be selectively and/or partially cationized to achieve the desire cationic state or zeta potential in order to function properly as an ionic liquid. FIG. 5B illustrates a comparison between the theoretical total number of amino acid groups (—COOH or NH.sub.2 or —OH) which may be modified with a positive charge and the actual number that were modified in a particular experiment. Out of a total of 144 —COOH groups (corresponding to line 1 of the graph presented on FIG. 5A), 115 of those were modified, leaving 29 —COOH groups unmodified.

(19) Next, the cationized antibodies are titrated with a counter anionic polymer (e.g. one or more of poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether (C.sub.9H.sub.19C.sub.6H.sub.4—(OCH.sub.2CH.sub.2).sub.20O(CH.sub.2).sub.3SO.sub.3), DL-lactate, linolenate, phospholipids, fatty acids, the conjugate base form of all amino acids, biologically-derived singly-charged anions, and small DL-peptide pairs) to create at least one antibody cation/anion pair in aqueous solution until the antibody cation/anion pair solution becomes negative by zeta potential measurement. The same methodology is applicable to each of the disclosed antibodies, generally applicable to all antibodies, and yields antibody ionic liquids which are stable and maintain efficacy up to 200° C., as illustrated in FIG. 7.

(20) FIG. 6 depicts the antigen binding of an aqueous antibody at room temperature (i.e. about 21-25° C.) 81 and at 100° C. 82 using a quartz crystal microbalance (QCM) to measure mass of antigen adsorbed to an antibody immobilized quartz sensor. FIG. 6 illustrates that an aqueous antibody solution cannot handle elevated temperatures, as is depicted by the change in frequency response as temperature increases. As the temperature increases to 100° C., the antibody solution exhibits decreasing binding activity until no binding activity is seen. That is, no binding is observed when a constant frequency value of 0 Hz+/−0.5 Hz over time is measured.

(21) FIG. 7 depicts the antigen binding of an ionic liquid antibody at room temperature (i.e. about 21-25° C.) 91 and at 200° C. 92 using a quartz crystal microbalance to measure mass of antigen adsorbed to an antibody immobilized quartz sensor. Binding is observed when the frequency decreases by more than about 2 Hz over time and a clear slope is observed vs. the initial baseline before antigen is added. FIG. 7 illustrates that an ionic liquid antibody solution can handle elevated temperatures and maintains functionality, as is depicted by the change in frequency response as temperature increases. As the temperature increases to 200° C., the antibody ionic liquid continues to exhibit binding activity similar to its performance at room temperature.

(22) Numerous anions were identified as possibilities for making an antibody liquid salt. However, non-biological polymer anions may trigger an immune response if used in vivo. A few biological anions were discovered to be amenable to making protein ionic liquids, including DL-lactate, linolenate, phospholipids, fatty acids, and combinations thereof, which are biocompatible. These are presented only as examples and the invention is not intended to be limited solely to those biological anions. Any biologically-derived anion with a low melting point (e.g. between about 5-30° C.) that known in the art may be used. The same methodology is generally applicable to all antibodies and yields antibody ionic liquids which are stable and maintain efficacy up to 200° C., as illustrated in FIG. 7.

(23) In one embodiment, creation of a water-free ultra-stable antibody ionic liquid, aqueous anti-hemoglobin antibodies produced in rabbits were cationized by addition of stoichiometric amounts of N,N-dimethyl-1,3-propanediamine in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) coupling reagent; addition of succinimidyl iodoacetate (SIA) and 2-(dimethylamino) ethanethiol; and/or N-(p-maleimidophenyl) isocyanate (PMPI) and 2-(dimethylamino) ethanethiol. After cationization, the cationized antibodies were purified from excess coupling reagents by repeated dialysis in water using dialysis membranes with molecular weight cutoffs (MWCO) of 7000 g/mol. Purification is an optional step. Cationized antibodies were confirmed by a positive zeta potential value.

(24) Next, the cationized antibodies were titrated with a corresponding non-toxic and bio-compatible counter anionic polymer of C.sub.9H.sub.19C.sub.6H.sub.4—(OCH.sub.2CH.sub.2).sub.20O(CH.sub.2).sub.3SO.sub.3 until positive charges on antibody became slightly negative by zeta potential measurements. This results in antibody cation/anion pairs which may be further processed to form an antibody ionic liquid.

(25) The antibody cation/anion pair was dialyzed repeatedly in water to remove excess anionic polymer using MWCO 7000 dialysis membranes and lyophilized to remove all water, i.e. at least 95% or at least 99%.

(26) Finally, lyophilized solid, e.g. powder, of the cationized anti-hemoglobin/anion pair was slowly, e.g. over a 20-minute period or more, heated to about 50° C. until a viscous clear liquid was generated. In one embodiment, the heating period is 30-90 minutes. In another embodiment, the cationized anti-hemoglobin pair is heated to 40-90° C. The anti-hemoglobin antibody ionic liquids were tested for antibody recognition of hemoglobin antigen using a dot blot assay on a nitrocellulose membrane and after heating at about 100° C. for 2 hours to test for temperature resistance. The antibody ionic liquid had retained its functionality, i.e. the functionality of its antibodies.

(27) The resulting antibody ionic liquids are ultra-stable, possess long shelf-lives (i.e. greater than about 5 years), do not require refrigeration for storage/handling/use, do not have to adhere to a cold supply chain, are resistant to extreme temperatures (such as temperatures greater than about 100° C.), are non-toxic and biologically compatible, and can be easily reconstituted into water or a biological buffer for therapeutic use. By comparison, antibodies in aqueous solutions have limited shelf-lives even with controlled refrigeration, are extremely sensitive to increased temperatures, and quickly lose all biological recognition activity. In one embodiment, antibody ionic liquids provided by the disclosed method may reduce costs associated with refrigeration and may also eliminate the substantial weight burden of heavy refrigeration equipment.

(28) In one embodiment, water-free antibody liquids may also be prepared by the disclosed method with anti-hemoglobin antibodies, anti-horse spleen ferritin IgG antibodies, or blood-typing IgM Anti-A antibodies, stable single chain antibodies from camelids, monoclonal Anti-Flag antibodies, monoclonal Anti-HRP2 to Plasmodium falciparum, polyclonal Anti-neuropeptide Y, and polyclonal Anti-human troponin, antibody fragments, or may contain combinations of multiple antibodies to create multi-recognition antibody liquids.

(29) Ultra-stable antibody liquids may permit refrigeration-free handling, storage and antibody-based diagnostics. They are resistant to extreme temperatures, have long shelf lives (e.g. a 20-fold improvement of the prior art), reduce the cost/weight load of specialized refrigeration equipment, and are able to be transported to underdeveloped countries while maintaining efficacy.

(30) In one exemplary embodiment, creation of a water-free ultra-stable photosystem II ionic liquid, containing photosystem II harvested from spinach leaves used for water splitting were cationized by the addition of stoichiometric amounts of N,N-dimethyl-1,3-propanediamine in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) coupling reagent; addition of succinimidyl iodoacetate (SIA) in the presence of 2-(dimethylamino) ethanethiol; and/or N-(p-maleimidophenyl) isocyanate (PMPI) in the presence of 2-(dimethylamino) ethanethiol. After cationization, the cationized photosystem II complex was purified from excess coupling reagents by repeated dialysis in water using dialysis membranes with molecular weight cutoffs (MWCO) of about 7000 g/mol. Cationized photosystem II complexes were confirmed by a positive zeta potential value. Although photosystem II protein complexes are used in this example, photosystem I, chlorophyll antennae, thylakoids, bacteriochlorophylls, chlorosomes, and photosystems from green algae, cyanobacteria, and plants are also acceptable and were demonstrated to be interchangeable.

(31) Next, cationized photosystem II (or photosystem I or other suitable protein complex) was titrated with a corresponding non-toxic and bio-compatible counter anionic polymer comprising at least one of C.sub.9H.sub.19C.sub.6H.sub.4—(OCH.sub.2CH.sub.2).sub.20O(CH.sub.2).sub.3SO.sub.3, DL-lactate, linolenate, phospholipids, fatty acids, the conjugate base form of all amino acids, biologically-derived singly-charged anions, or small DL-peptide pairs until positive charges on the cationized photosystems became slightly negative by zeta potential measurements.

(32) The photosystem cation/anion pair was dialyzed repeatedly in water to remove excess anionic polymer using MWCO 7000 dialysis membranes and lyophilized to remove all water, i.e. at least 95% or at least 99%.

(33) Finally, the lyophilized solid, e.g. powder, of the cationized photosystem II from spinach was electrostatically balanced with anions was slowly, e.g. over a 20-minute period or more, heated to about 50° C. until a viscous clear liquid was generated. In one embodiment, the heating period is 30-90 minutes. In another embodiment, the cationized photosystem II/anion pair is heated to 40-90° C. The cationized photosystem II ionic liquids were tested for stability by measuring the absorption spectrum and color appearance at room temperature over time. The cationized photosystem II ionic liquids were found to have retained their stability.

(34) FIG. 8 demonstrates the stability of photosystem II protein ionic liquids (cationized with EDC and N,N-dimethyl-1,3-propanediamine, and Poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether as the anion) as compared with native photosystem II complexes in water. As depicted, in water, the protein complexes have decomposed by day 9, even though kept at a cold temperature (4° C.). However, the photosystem II ionic liquid is stable at day 60 at 25° C. Ultra-stable photosystem ionic liquids may permit refrigeration-free handling, storage, and light harvesting of water-splitting materials. They are resistant to extreme temperatures, have long shelf lives (e.g. a 20-fold improvement of the prior art), reduce the cost/weight load of specialized refrigeration equipment, and are able to be transported to underdeveloped countries while maintaining efficacy. This stability affords a great advantage to those who process and utilize such photosystem complexes for tasks such as water-splitting. The functionality and photochemical activity of photosynthetic proteins and complexes is expected to be independent of any surface modifications (cationization) since they are buried within membranes for support and stability. As a further consideration, photochemical reactions occur intramolecularly within the protein interior as compared to antibody-antigen binding which is strictly surface based.

(35) In one embodiment, water-free protein ionic liquids may also be prepared with photosystem I from spinach, chlorophyll antennae, thylakoids, bacteriochlorophylls, and chlorosomes to create specialized light harvesting protein ionic liquids.

(36) While the present invention has been illustrated by a description of one or more embodiments thereof and while these embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.