ALDITOL OXIDASE AND APPLICATION THEREOF

Abstract

An alditol oxidase and application thereof. The method uses D-glucose as a substrate to dock the alditol oxidase derived from Streptomyces coelicolor A3, and selects amino acid residues around an active center for saturation mutagenesis, and screens for alditol oxidase with D-glucose oxidizing activity by plate color development. An amino acid sequence of the alditol oxidase is shown in SEQ ID NO: 2 or SEQ ID NO: 4. The alditol oxidase has the activity of converting D-glucose to D-gluconic acid and D-glyceraldehyde to D-glyceric acid. By using the alditol oxidase, the conversion of D-glucose to pyruvic acid is realized by only three enzymes for the first time and does not depend on any coenzyme.

Claims

1. An alditol oxidase, with an amino acid sequence as shown in SEQ ID NO: 2 or SEQ ID NO: 4.

2. A gene encoding the alditol oxidase of claim 1.

3. The gene of claim 2, wherein the gene has a nucleotide sequence as shown in SEQ ID NO: 3 or SEQ ID NO: 5.

4. A recombinant vector or a recombinant strain comprising the gene of claim 2.

5. The recombinant vector or the recombinant strain of claim 4, wherein the recombinant vector uses pET28a as an expression vector.

6. The recombinant vector or the recombinant strain of claim 4, wherein the recombinant strain uses Escherichia coli BL21 (DE3) as a host.

7. A method of synthesizing pyruvic acid, comprising using D-glucose as a substrate, and synthesizing pyruvic acid through a catalytic reaction of an alditol oxidase, dehydratase and 2-keto-3-deoxy gluconate aldolase, wherein the alditol oxidase is the alditol oxidase of claim 1.

8. The method of claim 7, wherein final concentration of the alditol oxidase is 0.30.7 mg/mL, final concentration of the dehydratase is 0.30.5 mg/mL, and final concentration of the 2-keto-3-deoxy gluconate aldolase is 0.10.3 mg/mL in a reaction system.

9. The method of claim 8, the reaction system further comprising MgCl.sub.2, Tween 20 and manganese dioxide, wherein reaction temperature of the reaction system is 3842 C.

10. An application of the alditol oxidase of claim 1 in catalyzing oxidation of aldose, wherein the aldose is one or more selected from D-xylose, D-ribose, L-arabinose, D-erythrose, D-mannose and D-galactose.

Description

BRIEF DESCRIPTION

[0018] FIG. 1 is a reaction route for synthesizing pyruvic acid using D-glucose as a substrate by a multi-enzyme catalytic method in the prior art.

[0019] FIG. 2 shows relative enzyme activity of the alditol oxidase according to the present application for oxidizing D-glucose and D-glyceraldehyde.

[0020] FIG. 3 is a concentration-time curve of the three-enzyme catalytic reaction of the alditol oxidase according to the present application using D-glucose as the substrate to synthesize pyruvic acid.

[0021] FIG. 4 is a liquid phase peak diagram of the three-enzyme catalytic reaction of the alditol oxidase according to the present application using D-glucose as the substrate to synthesize pyruvic acid.

[0022] FIG. 5 is a reaction route of the three-enzyme catalytic reaction according to the present application using D-glucose as the substrate to synthesize pyruvic acid.

[0023] FIG. 6 shows relative enzyme activity of the alditol oxidase according to the present application for oxidizing different aldoses.

DETAILED DESCRIPTION

[0024] The present application is described in detail below with embodiments so that those skilled in the art may better understand the application and be able to carry it out, however, the scope of protection of the present invention is not limited to these embodiments only. Wherein, amino acid substituted at original amino acid position is used to denote the mutated amino acid in an alditol oxidase, for example, the term AxxB means that an amino acid at position xx is replaced by amino acid B from amino acid A of a wild-type enzyme, and position number corresponds to an amino acid sequence number of the wild-type alditol oxidase in SEQ ID No: 1.

[0025] Full gene synthesis in the embodiments of the present application were performed by Suzhou GENEWIZ Biotechnology Co., Ltd.

[0026] Materials and reagents used in the embodiments of the disclosure are commercially available materials and reagents, unless specified.

[0027] The reagents used in the embodiments of the present application are as follows:

[0028] LB medium: 10 g/L peptone, 5 g/L yeast powder, and 10 g/L NaCl were prepared with deionized water, kept at room temperature for later use after autoclaving.

[0029] TB medium: a LB medium contains 12 g/L peptone, 24 g/L yeast powder, 4 mL/L glycerol, and potassium phosphate buffer.

[0030] 1M Isopropyl -D-Thiogalactoside (IPTG) solution: 2.383 g IPTG was weighed and dissolved in deionized water, which was diluted to 10 mL after complete dissolution, and then dispensed into 2 mL preservation tube and kept frozen at 20 C. for later use

[0031] Kanamycin solution (50 mg/mL): 0.5 g kanamycin sulfate was weighed and dissolved in deionized water, which was diluted to 10 mL after complete dissolution, and then dispensed into 2 mL preservation tube and kept frozen at 20 C.

[0032] In the following embodiments, the enzymes used are expressed by Escherichia coli BL21 (DE3), such as alditol oxidase, dehydratase (DHT), and 2-keto-3-deoxy gluconate aldolase (KDGA).

[0033] In a preferred embodiment of the application, the method of preparing the alditol oxidase in this present application includes the following steps: (1) constructing a gene of a corresponding mutation site of the alditol oxidase into a pET28a expression vector to obtain a recombinant plasmid with a target enzyme gene. (2) transferring the recombinant plasmid into a host cell to obtain a corresponding engineered strain, wherein the host cell is preferably Escherichia coli BL21 (DE3). (3) inoculating the engineered strain into the LB medium, culturing at 37 C. overnight, then transferring to the TB medium with an initial OD value of 0.1 controlled and culturing until the OD value reaches above 0.6, then adding 0.1 mM-1 mM IPTG and culturing at 12-30 C. for 12-20 hours. (4) collecting the strain by centrifugation.

Example 1: Construction of Alditol Oxidase Genetically Engineered Strain

(1) Construction of Gene Expression Vector

[0034] A wild-type alditol oxidase gene (Gene ID: 1101588) from Streptomyces coelicolor A3 containing mutations at four sites, V125M, A244T, V133M and G399R, was obtained through NCBI, and its amino acid sequence is shown in SEQ ID NO: 1. After codon optimization of the wild-type alditol oxidase sequence, the optimized sequence was synthesized by full gene synthesis and subcloned into the gene expression vector pET28a in Escherichia coli to obtain a recombinant plasmid pET28a-ScALDO.

(2) Construction of BL21 (DE3) Genetically Engineered Strain for Expression of Enzymes Related to Step (1)

(21) Transformation of Recombinant Plasmid into Escherichia Coli Competent Cell

[0035] The recombinant plasmid pET28a-ScALDO constructed in step (1) was transformed into an Escherichia coli expression host BL21 (DE3) by a calcium chloride method.

[0036] The BL21 (DE3) competent cell was placed on ice for 2 min in an ultra-clean bench to melt, and the recombinant plasmid, pET28a-ScALDO, was added into the BL21 (DE3) competent cell, gently blown to make them mixed evenly, and then stood on ice for 5 min, and then coated on a LB-resistant plate containing 50 mg/L kanamycin, and cultured in an incubator at 37 C. overnight.

(22) Colony PCR Identification

[0037] Positive single colonies were picked from the plates in step (21) and preliminary identification by colony PCR was carried out with 2Utaq PCR MasterMix (Beijing Zoman Biotechnology Co., Ltd., Catalog No. ZT201A-1). A colony PCR reaction system is shown in Table 1, and a colony PCR amplification reaction program is shown in Table 2. After colony PCR amplification, a colony PCR product was spotted into the wells of 1% agarose gel electrophoresis gel (another well of DS 5000 DNA Marker was spotted as a control), and separated in an electrophoresis tank (110 V) for 30 min. After the separation, the agarose gel electrophoresis gel was immersed in Gelred staining solution for 15 min. The approximate size of colony PCR product bands was then determined in a gel imaging instrument according to the DS 5000 DNA Marker and compared with the expected band size to determine whether expression strain construction was completed. In this embodiment, positive transformants were identified by colony PCR and expression strain BL21(DE3)/pET28a-ScALDO was obtained.

TABLE-US-00001 TABLE 1 Colony PCR Reaction System System Volume/L 2 Utaq PCR MasterMix 5 Upstream Primer 0.4 Downstream primer 0.4 Single colony Sterilized double-distilled water 4.2

TABLE-US-00002 TABLE 2 Colony PCR Amplification Reaction Program Program temperature( C.) time Cycle number Pre-denaturation 94 5 min 1 Denaturation 94 30 sec Annealing 55 30 sec {close oversize brace} 30 Extension 72 2.5 min Extension 72 10 min 1 Hold 16

Example 2: Construction and Screening of Mutant Alditol Oxidases

(1) Construction of Mutation Library of Alditol Oxidase

[0038] A saturation mutation library was constructed by docking wild-type alditol oxidase (amino acid sequence shown as SEQ ID NO: 1) with D-glucose as the substrate and selecting amino acid residues around an active center for saturation mutation.

(2) Screening of Mutant Alditol Oxidases that Simultaneously Oxidizing D-Glucose and D-Glyceraldehyde

[0039] The saturation mutation library was transformed into Escherichia coli BL21 (DE3) competent cells, which were subsequently coated onto a LB-resistant plate containing 50 mg/L kanamycin and cultured in an incubator at 37 C. overnight. The monoclonal colonies were screened for activity using a laboratory-developed plate coloration strategy, the basic principle of which is that the mutant alditol oxidase with catalytic activity releases H.sub.2O.sub.2 during the oxidation of the substrate glucose, and thus monoclonal colonies can be color-coded by the H.sub.2O.sub.2 coloration system for rapid identification of active mutations.

[0040] Two mutant strains with D-glucose oxidizing activity were obtained by screening, and the two mutant strains were cultured and plasmids thereof were extracted for DNA sequencing. The sequencing results showed that the mutation sites which enabled the mutant alditol oxidase to have D-glucose oxidizing activity were Q288G single mutation (corresponding to the mutation of the glutamine to glycine at position 288 of the amino acid sequence SEQ ID NO: 1) and Q288A single mutation (corresponding to the mutation of the glutamine to alanine at position 288 of the amino acid sequence SEQ ID NO: 1).

[0041] The mutant alditol oxidase containing a single mutation of Q288G was named ScALDO-Q288G, its amino acid sequence was SEQ ID NO: 2, the coding nucleotide sequence was SEQ ID NO: 3, and the corresponding expression strain was BL21 (DE3)/pET28a-ScALDO-Q288G. The mutant alditol oxidase containing a single mutation of Q288A was named ScALDO-Q288A, its amino acid sequence was SEQ ID NO: 4, the coding nucleotide sequence was SEQ ID NO: 5, and the corresponding expression strain was BL21 (DE3)/pET28a-ScALDO-Q288A.

Example 3: Construction of Genetically Engineered Strains for Dehydratase and 2-keto-3-deoxy Gluconate Aldolase

[0042] Dehydratase gene (NCBI Reference Sequence: WP_132585145.1) from Paralcaligenes ureilyticus, and a 2-keto-3-deoxy gluconate aldolase gene (NCBI Reference Sequence: NC_005877.1) from Picrophilus torridus were obtained through literature. After codon optimization of the dehydratase and 2-keto-3-deoxy gluconate aldolase sequence, the optimized sequence was synthesized by full gene synthesis and subcloned into the gene expression vector pET28a in Escherichia coli to obtain the recombinant plasmid pET28a-PuDHT and pET28a-PtKDGA respectively.

[0043] The pET28a-PuDHT, pET28a-PtKDGA recombinant plasmids were transformed into the Escherichia coli expression host BL21 (DE3) by a calcium chloride method, respectively, and the positive transformants were identified and expression strain BL21 (DE3)/pET28a-PuDHT and BL21 (DE3)/pET28a-PtKDGA were obtained.

Example 4: Induced Expression and Purification of Enzyme

[0044] The wild-type genetically engineered strains and mutant genetically engineered strains constructed in examples 13, that is BL21 (DE3)/pET28a-ScALDO, BL21 (DE3)/pET28a-PuDHT, BL21 (DE3)/pET28a-PtKDGA, BL21 (DE3)/pET28a-ScALDO-Q288G, BL21 (DE3)/pET28a-ScALDO-Q288A, were inoculated into 10 mL of LB medium containing 50 mg/L kanamycin, respectively, and cultured overnight at 37 C., 250 rpm to obtain seed solutions.

[0045] The seed solutions were inoculated separately in 100 mL of TB medium containing 50 mg/L of kanamycin, and the starting OD.sub.600 of a fermentation medium was controlled to be 0.1, and the fermentation medium was incubated at 37 C. and 220 rpm. When the fermentation medium was cultured to an OD.sub.600 of 0.6 or more, 50 L of 1 M IPTG was added for induction, so that the final concentration of IPTG in the fermentation medium was 0.5 mM, and the fermentation medium was placed at 16 C., 180 rpm for induction for 16 h.

[0046] After the induction, cell suspension was transferred to a 100 mL centrifuge tube and centrifuged at 6000 rpm for 5 min at room temperature; the supernatant was discarded and resuspended with sterile water, and centrifuged at 6000 rpm for 5 min at room temperature, and the supernatant was discarded. A certain volume of HEPES buffer was added to the above centrifuged bacterial precipitates respectively, which were then put into Toshiba ultrasonic crusher to sonicate for 3 s at 35% power, with an interval of 3 s, for a total of 40 min; then centrifuged at 4 C., 10,000 rpm for 30 min, to obtain crude enzyme solutions.

[0047] Purification of a target protein was carried out using an AKTA purifier and a nickel ion affinity chromatography column with an imidazole concentration of 0.3 M-0.5 M to obtain the target protein; subsequently, a desalting column was used to remove imidazole from the target protein.

Example 5: Enzyme Activity Assay of Wild-Type and Mutant Alditol Oxidases

[0048] Testing the relative activity of wild-type and mutant alditol oxidase on D-glucose: the system contained 10 mM D-glucose, 1 mM 4-AAP, 1 mM DHBS, 4 L of horseradish peroxidase at a concentration of 0.3 g/L, and 0.1 mg/mL of wild-type or mutant alditol oxidase. The enzyme activity of ScALDO, SCALDO-Q288G and ScALDO-Q288A on D-glucose was calculated by measuring the absorbance change of the system within 5 minutes, and the relative enzyme activity was calculated when the highest enzyme activity defined as 100%.

[0049] Testing the relative activity of wild-type and mutant alditol oxidase on D-glyceraldehyde: the system contained 10 mM D-glyceraldehyde, 1 mM 4-AAP, 1 mM DHBS, 4 L of horseradish peroxidase at a concentration of 0.3 g/L, and 0.1 mg/mL of wild-type or mutant alditol oxidase. The enzyme activity of ScALDO, ScALDO-Q288G and ScALDO-Q288A on D-glyceraldehyde was calculated by measuring the absorbance change of the system within 5 minutes, and the relative enzyme activity was calculated when the highest enzyme activity defined as 100%.

[0050] Referring to FIG. 2, it shows the relative enzyme activity of the alditol oxidases of the present application for oxidizing D-glucose and D-glyceraldehyde. The wild-type alditol oxidase ScALDO does not have the activity of oxidizing D-glucose to D-glucuronic acid and has highly substrate specificity. The mutant alditol oxidases ScALDO-Q288G and ScALDO-Q288A both show obvious activity in oxidizing D-glucose to D-gluconic acid, and retain a certain activity in oxidizing D-glyceraldehyde to D-glyceric acid. Both ScALDO-Q288G and ScALDO-Q288A achieve a high level of substrate promiscuity. Apparently, the Q288G site-directed mutation and the Q288A site-directed mutation endow the wild-type alditol oxidase ScALDO with a novel property of oxidizing both D-glucose and D-glyceraldehyde. Theoretically, the alditol oxidases of the present application (ScALDO-Q288G and ScALDO-Q288A) may replace glucose dehydrogenase (GDH) and glyceraldehyde dehydrogenase (ALDH) in the synthesis pathway of glucose to pyruvic acid, reducing the number of enzymes required for synthesizing pyruvic acid from D-glucose from four to three.

Example 6: Three-Enzyme-Catalytic Reaction for Pyruvic Acid Synthesis with Glucose as Substrate

[0051] 5 mM glucose, 5 mM MgCl.sub.2, 0.1% Tween 20, 1 g/L manganese dioxide, 0.5 mg/mL alditol oxidase (ScALDO-Q288G), 0.4 mg/mL dehydratase (PuDHT), 0.2 mg/mL 2-keto-3-deoxy gluconate aldolase (PtKDGA) were added into the reaction system, and the system reacted for 24 hours, in which 0.5 g/L manganese dioxide was added at 2 hours and 4 hours respectively. The reaction temperature of the reaction system was 40 C., the reaction pH was 8.0, the buffer was 100 mM HEPES-NaOH buffer, and the reaction system volume was 100 L. The alditol oxidase (ScALDO-Q288G) in the reaction system was replaced with the same amount of wild-type alditol oxidase ScALDO, the concentration of other substances remained unchanged, and the reaction was carried out under the same conditions for 24 hours as a control group.

[0052] The concentration of pyruvic acid in the three-enzyme reaction system of alditol oxidase ScALDO-Q288G, dehydratase PuDHT and 2-keto-3-deoxy gluconate aldolase PtKDGA at different reaction times was determined, and the concentration of pyruvic acid in the reaction system of control group was determined.

[0053] Referring to FIG. 3, it shows a concentration-time curve of the three-enzyme catalytic reaction for synthesizing pyruvic acid using D-glucose as a substrate. The three-enzyme reaction system of alditol oxidase ScALDO-Q288G, dehydratase PuDHT and 2-keto-3-deoxy gluconate aldolase PtKDGA may convert glucose into pyruvic acid, and the maximum conversion rate may reach 75.8%.

[0054] Referring to FIG. 4, it shows a liquid phase peak diagram of the three-enzyme catalytic reaction for synthesizing pyruvic acid using D-glucose as the substrate. No pyruvic acid was produced in the reaction system of the control group, which further indicated that the alditol oxidase of the application has unique substrate promiscuity.

[0055] Referring to FIG. 1 and FIG. 5, the oxidation of D-glucose to D-gluconic acid and the oxidation of D-glyceraldehyde to D-glyceric acid were carried out by two enzymes, glucose dehydrogenase and glyceraldehyde dehydrogenase, respectively in all reports. In this embodiment, the reaction circuit of the three-enzyme catalytic reaction using the alditol oxidase of the application to synthesize pyruvic acid with D-glucose as the substrate was as follows: one molecule of D-glucose was converted into one molecule of D-gluconic acid catalyzed by alditol oxidase, and then one molecule of D-gluconic acid was converted to 2-keto-3-deoxy gluconic acid catalyzed by dehydratase PuDHT. Subsequently, 2-keto-3-deoxy gluconic acid was catalyzed by 2-keto-3-deoxy gluconate aldolase PtKDGA to convert to one molecule of D-glyceraldehyde and one molecule of pyruvic acid, one molecule of D-glyceraldehyde was catalyzed by alditol oxidase to convert to one molecule of D-glyceric acid, and one molecule of D-glyceric acid was catalyzed by dehydratase PuDHT to convert to another molecule of pyruvic acid. One molecule of glucose may theoretically be converted into two molecules of pyruvic acid. Compared with other studies, the glucose dehydrogenase (GDH) and glyceraldehyde dehydrogenase (ALDH) required for the synthesis of pyruvic acid from D-glucose were replaced by the alditol oxidase provided in the present application, and the number of enzymes required for the synthesis of pyruvic acid from D-glucose was reduced from four to three, and the dependence on cofactor NAD+ was eliminated.

[0056] Therefore, the present application provides an alditol oxidase ScALDO-Q288G and ScALDO-Q288A, which has a new property of simultaneously oxidizing D-glucose and D-glyceraldehyde, and may reduce the number of enzymes required for synthesizing pyruvate from D-glucose from 4 to 3 for the first time, and does not depend on any coenzyme, and has great originality and application value.

Example 7: Application of Mutant Alditol Oxidase in the Oxidation of Various Aldoses

[0057] This embodiment tested the oxidation activity of wild-type and mutant alditol oxidases (ScALDO, ScALDO-Q288G, and ScALDO-Q288G) provided in the present application on various aldoses, including D-xylose, D-ribose, L-arabinose, D-erythrose, D-mannose, and D-galactose. In the process of oxidizing aldose, alditol oxidase will release H.sub.2O.sub.2, and the released H.sub.2O.sub.2 and 4-AAP, DHBS generated chromogenic substances under the catalysis of horseradish peroxidase. By detecting the generation of chromogenic substances at 515 nm wavelength, the oxidation activity of wild-type or mutant alditol oxidase on aldose was tested, and the relative enzyme activity was calculated when the highest enzyme activity defined as 100%.

[0058] Referring to FIG. 6, it shows the relative enzyme activity of alditol oxidases (ScALDO-Q288G and ScALDO-Q288G) for oxidizing different aldoses. Compared with wild-type alditol oxidase ScALDO, the enzyme activity of alditol oxidase SCALDO-Q288G (SEQ ID NO: 2) provided in the present application was increased by 59 folds, and the enzyme activity of alditol oxidase ScALDO-Q288A (SEQ ID NO: 4) provided in the present application was increased by 4.4 folds when D-xylose was used as the substrate.

[0059] Compared with wild-type alditol oxidase ScALDO, the enzyme activity of alditol oxidase SCALDO-Q288G (SEQ ID NO:2) provided in the present application was increased by 226.3 folds, and the enzyme activity of alditol oxidase ScALDO-Q288A (SEQ ID NO:4) provided in the present application was increased by up to 38.3 folds when D-ribose was used as the substrate.

[0060] Compared with wild-type alditol oxidase ScALDO, the enzyme activity of alditol oxidase SCALDO-Q288G (SEQ ID NO:2) provided in the present application was increased by 3.61 folds, and the enzyme activity of alditol oxidase ScALDO-Q288A (SEQ ID NO:4) provided in the present application was increased by 1.98 folds when L-arabinose was used as the substrate.

[0061] Compared with wild-type alditol oxidase ScALDO, the enzyme activity of alditol oxidase SCALDO-Q288G (SEQ ID NO:2) provided in the present application was increased by 1.9 folds, and the enzyme activity of alditol oxidase ScALDO-Q288A (SEQ ID NO:4) provided in the present application was increased by 1.9 folds when D-erythrose was used as the substrate.

[0062] Compared with wild-type alditol oxidase ScALDO, the enzyme activity of alditol oxidase SCALDO-Q288G (SEQ ID NO:2) provided in the present application was increased by 3.2 folds, and the enzyme activity of alditol oxidase ScALDO-Q288A (SEQ ID NO:4) provided in the present application was increased by 2.9 folds when D-mannose was used as the substrate.

[0063] Compared with wild-type alditol oxidase ScALDO, the enzyme activity of alditol oxidase SCALDO-Q288G (SEQ ID NO:2) provided in the present application was increased by 5.1 folds, and the enzyme activity of alditol oxidase ScALDO-Q288A (SEQ ID NO:4) provided in the present application was increased by 3.7 folds when D-galactose was used as the substrate.

[0064] The above embodiments are only a description of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and changes made by ordinary skill person in the art to the technical solutions of the present invention should fall within the protection scope determined by claims of the present invention.