Patent Application
20230193215
The present invention relates to the field of genetic engineering, particularly to glucose oxidase mutants having improved thermal stability, gene and application thereof.
Glucose oxidase (GOD) is an important oxidase and belongs to the glucose/methol/choline (GMC) oxidoreductase family GOD specifically catalyzes the substrate β-D-glucose to produce gluconic acid and hydrogen peroxide with oxygen. The mechanism of glucose oxidation is the oxidoreductase system consisting of glucose oxidase and catalase, wherein glucose oxidase can oxidize glucose to produce D-gluconolactone in the presence of molecular oxygen taking FAD as cofactor and consume oxygen to produce hydrogen peroxide, and catalase can decompose hydrogen peroxide into water capable of combining with glucolactone to produce gluconic acid and oxygen. GOD is a homodimeric enzyme polymerized by two 80 KD monomers together, each of which contains two regions, wherein one binds to FAD in a noncovalent form and the other binds to substrate β-D glucose. GDO is widely distributed in animals, plants and microorganisms wherein microorganisms are the main source producing GOD as they have the characteristics of fast growth and reproduction and wide variety. And, the main production strains are Aspergillus niger and penicillin.
GOD is widely used in the fields of chemistry, pharmacy, food, clinical diagnosis, biotechnology and so on, wherein GOD is added to feed to inhibit the growth of nutritious microorganisms and kill harmful intestinal microorganisms, produces gluconic acid capable of improving the pH of the intestine and facilitating the absorption of nutrients in the field of animal feed, and is also widely used in the food industry by being added during in the brewing process to resist oxidation, maintain flavor and preserve for a long time, because oxygen will be consumed in the catalytic process of glucose oxidase, and being added in bread production to improve the quality of flour, the specific volume and the aging resistance. The application filed of GOD is expanding based on its properties, and the requirement of market is increasing sharply. However, the defects of low yield and low enzyme activity limit its industrial development. CN108893453A disclosed a glucose oxidase mutant GOD-M5 muted from GOD derived from Aspergillus niger. Although thermal stability of glucose oxidase mutant GOD-M5 has been improved, it still couldn't meet the industrial requirements.
The order of the present invention is to provide glucose oxidase mutants GOD-M6, GOD-M7, GOD-M8, GOD-M9 and GOD-M10.
Another order of the present invention is to provide gene encoding any one of the above glucose oxidase GOD mutants.
Another order of the present invention is to provide a recombinant vector containing the genes encoding any one of the above glucose oxidase GOD mutants.
Another order of the present invention is to provide a recombinant strain containing the gene encoding any one of the above glucose oxidase GOD mutants.
Another order of the present invention is to provide a genetic engineering method for preparing any one of the above glucose oxidase GOD mutant2.
Another order of the present invention is to provide application of any one of the above glucose oxidase GOD mutants.
In a preferred embodiment of the present invention, the amino acid sequence of the glucose oxidase GOD mutant GOD-M5 is shown in SEQ ID NO: 1.
In a yet preferred embodiment of the present invention, Asp of position 68 of the glucose oxidase GOD mutant GOD-M5 is substituted with Lys to obtain the glucose oxidase mutant GOD-M6; Thr of position 274 of the glucose oxidase GOD mutant GOD-M6 is substituted with Phe, and Tyr of position 278 of the glucose oxidase GOD mutant GOD-M6 is substituted with Thr to obtain the glucose oxidase mutant GOD-M7; Ser of position 94 of the glucose oxidase GOD mutant GOD-M7 is substituted with Ala to obtain the glucose oxidase mutant GOD-M8; Thr of position 31 of the glucose oxidase GOD mutant GOD-M8 is substituted with Val to obtain the glucose oxidase mutant GOD-M9; and Gln of position 88 of the glucose oxidase GOD mutant GOD-M9 is substituted with Arg to obtain the glucose oxidase mutant GOD-M10.
In a further preferred embodiment, the amino acid sequence of the glucose oxidase mutant GOD-M6 is shown in SEQ ID NO: 2.
In a further preferred embodiment, the amino acid sequence of the glucose oxidase mutant GOD-M7 is shown in SEQ ID NO:3.
In a further preferred embodiment, the amino acid sequence of the glucose oxidase mutant GOD-M8 is shown in SEQ ID NO:4.
In a further preferred embodiment, the amino acid sequence of the glucose oxidase mutant GOD-M9 is shown in SEQ ID NO:5.
In a further preferred embodiment, the amino acid sequence of the glucose oxidase mutant GOD-M10 is shown in SEQ ID NO:6.
The present invention provides a gene encoding the above glucose oxidase GOD mutant.
In a further preferred embodiment, the nucleotide sequence of the gene god-m5 encoding the glucose oxidase mutant GOD-M5 is shown in SEQ ID NO:7.
In a further preferred embodiment, the nucleotide sequence of the gene god-m6 encoding the glucose oxidase mutant GOD-M6 is shown in SEQ ID NO:8.
In a further preferred embodiment, the nucleotide sequence of the gene god-m7 encoding the glucose oxidase mutant GOD-M7 is shown in SEQ ID NO:9.
In a further preferred embodiment, the nucleotide sequence of the gene god-m8 encoding the glucose oxidase mutant GOD-M8 is shown in SEQ ID NO:10.
In a further preferred embodiment, the nucleotide sequence of the gene god-m9 encoding the glucose oxidase mutant GOD-M9 is shown in SEQ ID NO:11.
In a further preferred embodiment, the nucleotide sequence of the gene god-m10 encoding the glucose oxidase mutant GOD-M10 is shown in SEQ ID NO:12.
In a further preferred embodiment, the bases GAC of position 202 to 204 of the gene god-m5 are muted into the bases AAA to obtain the gene god-m6 encoding said mutant GOD-M6; the bases ACC of position 820 to 822 of the gene god-m6 are muted into the bases TTT, and TTA of position 832 to 834 of the gene god-m6 are muted into the bases ACC to obtain the gene god-m7 encoding said mutant GOD-M7; the bases TCC of position 280 to 282 of the gene god-m7 are muted into the bases GCT to obtain the gene god-m8 encoding said mutant GOD-M8; the bases ACT of position 90 to 93 of the gene god-m8 are muted into the bases GTT to obtain the gene god-m9 encoding said mutant GOD-M9; and the bases AGA of position 262 to 264 of the gene god-m9 are muted into the bases CAA to obtain the gene god-m10 encoding said mutant GOD-M10.
The present invention provides recombinant vector comprising the gene encoding the abovementioned glucose oxidase GOD.
The present invention provides a recombinant strain comprising the above gene encoding the glucose oxidase GOD mutant. Preferably, said recombinant strain is Pichia pastoris strains GS115/GOD-M6, GS115/GOD-M7, GS115/GOD-M8, GS115/GOD-M9, and GS115/GOD-M10.
In a further preferred embodiment, the method of preparing glucose oxidase GOD with the improved thermal stability and catalytic activity comprises the following steps of transforming the host cells with the recombinant vector containing the gene encoding the above glucose oxidase GOD mutants to obtain the recombinant strains, culturing the obtained recombinant strains to induce the expression of recombinant glucose oxidase GOD mutants, and recovering and purifying the glucose oxidase GOD.
After being treated at 70° C. for 10 min, the relative residual enzyme activities of the glucose oxidase mutant GOD-M5 are 55%, and the relative residual enzyme activity of mutants GOD-M6, GOD-M7, GOD-M8, GOD-M9 and GOD-M10 is 60%, 71%, 75%, 99%, 100% respectively, demonstrating the glucose oxidase mutant of the present having improved thermal stability.
After treated at 80° C. for 2 min, the relative residual enzyme activity of the glucose oxidase mutant GOD-M5 is 35%, and the relative residual enzyme activity of mutants GOD-M6, GOD-M7, GOD-M8, GOD-M9 and GOD-M10 is 40%, 55%, 60%, 72%, 80% respectively, demonstrating the glucose oxidase mutant of the present having improved thermal stability wherein the relative residual enzyme activity of the mutant GOD-M10 is about 2.2 times of that of the mutant GOD-M5.
The present invention provides several glucose oxidase GOD mutants with high catalytic efficiency and improved thermal stability, which breaks the barrier of low enzyme activity and poor stability and is suited well to meet the requirements of application to the fields of food, medicine, feed and textile industry, and has a very broad application prospect.
Test Materials and Reagents
1. Strains and vectors: Pichia pastoris GS115 and expressing vector pPIC9.
2. Enzymes and other biochemical reagents: point mutation kit and other biochemical reagents were purchased by biochemical reagent company.
3. Medium:
LB medium: 5% yeast extract, 1% peptone, 1% NaCL, pH 7.0;
BMGY medium: 1% yeast extract, 2% peptone, 1% glycerol (V/V), 1.34% YNB, 0.00004% Biotin;
BMMY medium: 1% yeast extract, 2% peptone, 1.34% YNB, 0.00004% Biotin, 0.5% methanol (V/V).
Suitable biology laboratory methods not particularly mentioned in the examples as below can be found in Sambrook, et al. (Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989), and other kit laboratory manuals.
The glucose oxidase mutant GOD-M5 was obtained by the steps of substituting amino acid Glu of position 82 of the glucose oxidase GOD having the acid sequence of SEQ ID No:1 from Aspergillus niger with the amino acid Cys to obtain the mutant GOD-M1, substituting the amino acid Val of position 418 of GOD-M1 with the amino acid Glu to obtain the mutant GOD-M2, substitute amino acid Asn of position 508 of GOD-M2 with the amino acid His to obtain the mutant GOD-M3, substituting the amino acid Thr of position 32 of GOD-M3 with the amino acid Val to obtain the mutant GOD-M4, and substituting the amino acid Asp of position 313 of GOD-M4 with the amino acid Lys to obtain the mutant GOD-M5.
And, Asp of position 68 of the glucose oxidase mutant GOD-M5 was muted into Lys using the recombinant plasmid pPIC9-godm5 as the temple to the mutant GOD-M6; Thr of position 274 of the glucose oxidase GOD mutant GOD-M6 is muted into Phe, and Tyr of position 278 of the glucose oxidase GOD mutant GOD-M6 is muted into Thr to obtain the glucose oxidase mutant GOD-M7; Ser of position 94 of the glucose oxidase GOD mutant GOD-M7 is muted into Ala to obtain the glucose oxidase mutant GOD-M8; Thr of position 31 of the glucose oxidase GOD mutant GOD-M8 is muted into Val to obtain the glucose oxidase mutant GOD-M9; and Gln of position 88 of the glucose oxidase GOD mutant GOD-M9 is muted into Arg to obtain the glucose oxidase mutant GOD-M10, wherein the mutation sites were introduced by site directed mutagenesis PCR and verified by sequencing. The primers for PCR were shown in Table 1:
The PCR was performed by taking the recombinant plasmid pPIC9-godm5 as the template with the site directed mutagenesis reagent, followed by verifying by nucleic acid gel, adding 1 μL of DMT enzyme to the PCR product, mixing well and incubating at 37° C. for 1 hour. The PCR product was demethylated by 2 to 5 μL of DMT enzyme and transformed into DMT competent cells, followed by selecting monoclonal cells and verifying the positive transformants by DNA sequencing. The transformants confirmed by sequencing were used to prepare a large number of recombinant expression plasmids which were linearized with restriction endonuclease Bgl II, followed by transforming yeast GS115 competent cells by electric shock, culturing at 30° C. for 2 to 3 days, and selecting the transformants growing on MD plate for further expression experiment by referring to Pichia pastoris expression operation manual. The selected positive clones comprising the glucose oxidase mutants by color reaction on MM plate were GS115/GOD-M5, GS115/GOD-M6, GS115/GOD-M7, GS115/GOD-M8, GS115/GOD-M9 and GS115/GOD-M10 respectively.
(1) High Expression of Glucose Oxidase in Pichia pastoris at Shake Flask Level
GS115 strain containing recombinant plasmid was inoculated into 300 mL of BMGY medium and incubated for 48 h at 30° C. and 220 rpm, followed by centrifuging at 4500 g for 5 min to remove the supernatant. The obtained precipitate was suspended for 48 hour in 200 mL of BMMY medium containing 0.5% of methanol to induce at 30° C. and 220 rpm with addition of 0.5 mL of methanol every 12 h to keep the concentration of methanol in the bacterial solution as 0.5%. After induction, the supernatant was recovered by spinning to test the activity of the enzyme and SDS page.
(2) Purification of Recombinant Glucose Oxidase
The supernatant of the recombinant glucose oxidase expressed in the shaking bottle was collected followed by being concentrated with 10 kDa membrane package while replacing the medium of the fermentation broth with 10 mM of disodium hydrogen phosphate citric acid buffer with pH of 6.5, and further purified by anion exchange column
The enzyme activity was determined by mixing 2.5 mL of o-anisidine buffer prepared by adding 0.2 mL of 1% o-anisidine to 25 mL of phosphate buffer in 0.1 M, 300 μL of 18% of glucose solution, 100 μL of 0.03% of horseradish peroxidase, and 100 μL of appropriate diluted release enzyme solution at pH6.0 to react for 3 min at 30° C., followed by adding 2 ml of H2SO4 in 2M to terminate the reaction and measuring the absorbance value at 540 nm. A unit of enzyme activity (U) is defined as the amount of enzyme required to produce 1 μmol gluconic acid and hydrogen peroxide per unit time under given conditions.
Measuring the enzyme activity and thermal stability of glucose oxidase GOD mutant and the parent glucose oxidase mutant GODMS as below.
1. The enzyme activities of the glucose oxidase GOD mutant purified in example 3 and the parent glucose oxidase mutant GODMS were determined by performing the enzymatic reaction at pH 6.0 and 30° C.
The specific activity of the parent glucose oxidase mutant GODMS was 366U/mg, and the activities of the mutants GOD-M6, GOD-M7, GOD-M8, GOD-M9 and GOD-M10 were 301.1 U/mg, 299.3 U/mg, 197.9 U/mg, 454 U/mg and 445.3 U/mg, respectively, wherein the specific activity of GOD-M10 was 1.2 times of that of GOD-M5.
2. Measuring the Thermal Stability of the Mutants and the Parent at 70° C. or 80° C.
The mutant glucose oxidase GOD and the parent were treated at 70° C. for 0, 2, 5, 10, 20, and 30 min respectively and 80° C. for 0, 1, 2 and 5 min respectively in 0.1 mol/L of citric acid disodium hydrogen phosphate buffer (pH 6.0), followed by measuring the relative residual enzyme activity at 30° C.
As shown in
And, as shown in
3. Determining the Optimum Temperature of Glucose Oxidase Mutants and the Parent
The enzyme activities of GOD-M5, GOD-M6, GOD-M7, GOD-M8, GOD-M9 and GOD-M10 were measured at 0, 20, 30, 40, 50, 60, 70 and 80° C. in pH of 6.0. As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 201910681815.3 | Jul 2019 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2019/117826 | 11/13/2019 | WO |
