CN116004576A - alpha-L-rhamnosidase BtRha78A mutant and preparation method and application thereof - Google Patents

Abstract

The invention relates to the fields of enzyme engineering and genetic engineering, in particular to an alpha-L-rhamnosidase BtRha78A mutant and a preparation method and application thereof. The amino acid sequence of the mutant has one amino acid mutation with BtRha78A enzyme shown in SEQ ID NO.1, and the mutation is that phenylalanine at 44 th position is mutated into aspartic acid or serine. The mutant of the invention has higher catalytic efficiency in a short time, and provides theoretical guidance for realizing industrialization of preparing isoquercitrin by hydrolyzing rutin in a large amount.

Description

alpha-L-rhamnosidase BtRha78A mutant and preparation method and application thereof

Technical Field

The invention relates to the fields of enzyme engineering and genetic engineering, in particular to an alpha-L-rhamnosidase BtRha78A mutant and a preparation method and application thereof.

Background

alpha-L-rhamnosidase is an important biotechnological enzyme that hydrolyzes the L-rhamnose at the end of most natural products, such as rutin, hesperidin, ginsenoside etc. Is widely distributed in bacteria, fungi, plants, animal tissues and the like. For industrial, pharmaceutical pretreatment, food production, etc., it is useful, for example, for debitterizing fruit juice, enhancing grape juice by deglycosylation of terpenes, improving flavor of wine, etc. Rutin is derived from plants such as pagodatree flower, tartary buckwheat and the like, belongs to flavonol, is disaccharide glycoside of quercetin, has wide pharmacological activity, comprises the effects of antioxidation, depressurization, anticancer, anti-influenza, anti-inflammatory and the like, and the isoquercitrin also has the pharmacological activity, but has the advantages of improving the stability of the compound, increasing the water solubility, reducing the toxic and side effects, improving the drug specificity and targeting property and the like because of the existence of glycoside, and draws the attention of more and more students. However, there are a great deal of technical barriers to the large-scale industrial and food production of α -L-rhamnosidase at present, and the use of α -L-rhamnosidase is limited due to the low activity of natural α -L-rhamnosidase and the uncomfortable reaction conditions.

With the continuous rising of protein engineering technology, modification and editing of protein sequences are started, and molecular modification is performed on required enzymes, so that the purpose enzymes are finally achieved. Currently, molecular engineering includes directed evolution, rational design and semi-rational design. Directed evolution is the low frequency introduction of randomly distributed mutations into a gene of interest, followed by selection of muteins with desired properties, which allow relatively rapid engineering of enzymes without the need for extensive knowledge of structural functional relationships, a major limitation being the need to develop a high throughput screening method; different from directed evolution, rational design requires deep knowledge of the sequence, structure and functional relationship of the modified enzyme, and finally determines the target point of the required mutation, and performs site-directed mutagenesis to study the characteristics of the target point; recent developments have used directed evolution in combination with rational design, i.e. semi-rational design, to remedy the above-mentioned drawbacks, and in brief, the method uses protein sequence and structural information, and related calculations to construct a smaller but intelligent mutant library for specific residues, and concerns about specific amino acid positions will lead to a significant reduction in library size, thus screening for excellent mutants.

The patent number is CN202010653391.2, the name is alpha-rhamnosidase, the coding gene thereof and the expression and application thereof, the alpha-rhamnosidase which is high-temperature resistant and heat stable can almost completely convert rutin into isoquercetin under proper conditions, the catalytic activity is still limited, but the molecular transformation technology is not involved; the patent number is CN202110692714.3, the name is a rhamnosidase mutant, and a preparation method and application thereof, and the alpha-L-rhamnosidase is semi-rationally designed to obtain a high-activity combined mutant which is not applied to the mass preparation of isoquercitrin. Therefore, semi-rational design of the alpha-L-rhamnosidase BtRha78A to obtain the alpha-L-rhamnosidase excellent mutant with high efficiency of hydrolyzing rutin to generate isoquercitrin is a significant research direction.

Disclosure of Invention

In order to solve the technical problems, the invention provides an alpha-L-rhamnosidase BtRha78A mutant and a preparation method and application thereof.

In a first aspect, the invention provides a mutant of alpha-L-rhamnosidase BtRha78A, the amino acid sequence of the mutant has one amino acid mutation with the BtRha78A enzyme shown in SEQ ID NO.1, and the mutation is that phenylalanine at position 44 is mutated into aspartic acid or serine.

In a second aspect, the invention provides a DNA molecule encoding said alpha-L-rhamnosidase BtRha78A mutant.

Further, the DNA molecule has any one of the nucleotide sequences shown in a1-a 3:

a1, SEQ ID NO.2 or SEQ ID NO. 3;

complementary sequences of the nucleotide sequences in a 2and a 1;

a3, a nucleotide sequence encoding said α -L-rhamnosidase BtRha78A mutant, and which differs from a1 and a2 due to the degeneracy of the genetic code.

In a third aspect, the present invention provides a recombinant expression vector having the DNA molecule.

In a fourth aspect, the invention provides a host cell comprising the recombinant expression vector.

In a fifth aspect, the invention provides a method for preparing the alpha-L-rhamnosidase BtRha78A mutant, comprising the following steps: inducing the host cell to express an alpha-L-rhamnosidase BtRha78A mutant, and separating and purifying the expressed alpha-L-rhamnosidase BtRha78A mutant.

In a sixth aspect, the invention provides an application of the alpha-L-rhamnosidase BtRha78A mutant in preparing isoquercetin by catalyzing rutin.

Compared with the prior art, the invention has the following beneficial effects:

1. according to the invention, the PyMOL is utilized to analyze the amino acid at the inlet of the alpha-L-rhamnosidase BtRha78A substrate, the 44 th is determined to be a mutation target spot, a new enzyme is semi-rationally designed for the mutant, an excellent mutant with higher catalytic efficiency in a short time is obtained, and theoretical guidance is provided for realizing industrialization of preparing isoquercitrin by hydrolyzing rutin in a large amount.

2. The rutin is catalyzed by whole cells and pure enzyme respectively, and the mutant reacts at 37 ℃ and pH 6.5. Under whole cell conditions, the conversion rate of WT was 33.9% and the conversion rates of F44S and F44D were 45.8% and 33.1% higher than that of WT, respectively, when the reaction time was 60 min. Under the pure enzyme condition, the reaction time is 20min, the WT conversion rate is only 10.7%, and the F44S conversion rate and the F44D conversion rate are respectively improved by 2.55 times and 1.38 times.

Drawings

FIG. 1 shows the amino acid residues in the substrate channel and its entrance in example 1.

FIG. 2 shows the relative activity of the alanine scanning mutant whole cell of example 1 on rutin catalysis.

FIG. 3 is a nucleic acid electrophoresis pattern of the whole plasmid PCR product of example 2.

FIG. 4 is a flow chart of the catalytic reaction in example 2.

FIG. 5 is a standard curve of rutin and isoquercitrin in example 2.

FIG. 6 shows evaluation of rutin hydrolysis activity of whole cells of the wild type and the mutant in example 2.

FIG. 7 shows SDS-PAGE of the purified target proteins of the wild type and mutant in example 3. Lane 1 in the figure represents Maker, and lanes 2-5 represent the purified target protein of WT, F44A, F44D, F S, respectively.

FIG. 8 is a plot of the time for the high activity mutant to catalyze rutin under the pure enzyme conditions of example 3.

FIG. 9 shows the catalytic activity of the excellent mutant on rutin at 20min of reaction time under pure enzyme conditions in example 3.

Detailed Description

The present invention will now be described in detail with reference to the drawings and specific examples, which should not be construed as limiting the invention. Unless otherwise indicated, the technical means used in the following examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used in the following examples are commercially available unless otherwise indicated.

The plasmid pET-28A-BtRha78A containing the alpha-L-rhamnosidase BtRha78A (amino acid sequence shown in SEQ ID NO. 1) referred to in the following examples was stored by the applicant laboratory and is disclosed in document Characterization of a glycoside hydrolase family 78A-L-rhamnosidase from Bacteroides thetaiotaomicron VPI-5482and identification of functional residues.

Example 1: determination of mutation site of alpha-L-rhamnosidase BtRha78A

The spatial structure of the alpha-L-rhamnosidase BtRha78A (PDB: 3 CIH) derived from the human intestinal bacterium Bacteroides thetaiotaomicron VPI-5482 was studied using Pymol, the amino acid residues at the substrate channel and its entrance were analyzed, 17 amino acid residues were determined as mutation targets, E39, F44, P45, P46, F47, W48, E233, T379, I380, W435, V436, F437, V438, D439, Y610, G611, R612, respectively, and the protein structure is shown in FIG. 1.

An alanine scanning mutant with 17 mutation sites is constructed, after heterologous expression, whole cells catalyze rutin to prepare isoquercetin, and the relative activities of the 17 mutants and WT are compared, as shown in figure 2, only F44A relative activity is found to be 32.8% higher than that of the WT, and the relative activities of the rest sites are smaller than that of the wild type, so that the site tolerance mutation degree is higher and the site has higher plasticity, and therefore, the site F44 is selected for site-specific saturation mutation.

Example 2: preparation and catalytic reaction of alpha-L-rhamnosidase BtRha78A mutant

1. F44 site-directed saturation mutant library construction

(1) Primer designs are shown in table 1;

TABLE 1 F44 site-directed saturation mutagenesis primer

(2) Plasmid pET-28A-BtRha78A _WT (see SanPrep column plasmid DNA miniextraction kit instructions). Carrying out full plasmid PCR by taking plasmid pET-28A-BtRha78A as a template, wherein a PCR system and a PCR program are shown in tables 2and 3;

TABLE 2 full plasmid PCR System

TABLE 3 full plasmid PCR procedure

(3) Nucleic acid electrophoresis: the PCR products were identified by 1% agarose gel electrophoresis, and the DL10000DNA Marker was used as the standard molecular weight, and the nucleic acid electrophoresis pattern was shown in FIG. 3, with the product band between 7000 and 10000bp, indicating that the whole plasmid PCR amplification was successful.

(4) Digestion of the template: adding 1 mu L of QuickCut Dpn I into the PCR product, and placing the mixture in a 37 ℃ metal bath to digest the template for 2 hours;

(5) The PCR product, wild type plasmid and BtRha78A-F44A plasmid (as positive control) were transformed into competent cells of E.coli BL21 (DE 3) and cultured in an incubator at 37℃for 12h.

2. Screening of F44 site-directed saturation mutant library and preparation of alpha-L-rhamnosidase BtRha78A mutant

(1) And (3) primary screening:

selecting monoclonal: 200. Mu.L of 2 XYT kanamycin-containing liquid medium was added to each well of the master, 252 clones were picked with sterilized toothpicks, and each 96-well plate master (3 total) contained 6 wild-type, 4 positive controls and 2 blank controls, incubated at 37℃with shaking overnight at a constant temperature of 150rpm (about 15 h);

and (3) fungus liquid transferring and preserving: adding 160 μL of 2 XYT kanamycin-containing liquid culture medium into each hole of a daughter board, then taking 20 μL of bacterial liquid from a mother board, respectively adding the bacterial liquid into the daughter board, carrying out constant-temperature shake culture on the daughter board at 37 ℃ and 150rpm for about 5.5 hours until the bacterial density OD600 = 1.0, adding 50 μL of 70% glycerol into each hole of the mother board, and temporarily storing in a refrigerator at-40 ℃;

induction of expression: 20. Mu.L of 5mM IPTG was added to each well of the daughter plate, and expression was induced at 16℃and 150rpm overnight (about 15 h);

screening reaction: centrifuging the bacterial liquid 3700rpm after the induction expression for 30min, discarding the supernatant, adding 100 mu L of premix (the premix contains rutin (the final concentration is 1 mM), beta-D glucosidase TnBgl1A-DM pure enzyme liquid (the final concentration is 0.02 mg/mL) and pH 6.5 50mM PB buffer buffer) into each hole, sucking and beating uniformly, carrying out reaction for 2h (alpha-L-rhamnosidase reaction), carrying out oven reaction for 30min at 80 ℃ for 30min (beta-D glucosidase reaction), adding 100 mu L of methanol for stopping reaction, carrying out 3700rpm, centrifuging for 30min (removing thalli and fragments), taking 60 mu L of supernatant, adding into a detection plate containing 140 mu L of sodium carbonate with pH of 10.0 mM (quercetin is subjected to autoxidation to form a polymer under the condition of alkaline pH of 10.0, and shows a maximum absorption peak at 320nm, which is called a characteristic peak of quercetin), standing for 30min at room temperature, and detecting the absorbance at 320nm by an enzyme marker.

Primary screening results: after the 252 mutants are subjected to primary screening, 75 mutants are selected to enter secondary screening.

(2) And (3) re-screening:

clones obtained by primary screening are respectively transferred to 5mL of 2 XYT kanamycin-containing liquid culture medium with 1% inoculum size from a mother plate, cultured at 37 ℃ and 180rpm until OD600 = 1.0, added with 5 mu L of 0.5M IPTG and induced to express for 12-14h at low temperature overnight, and thalli are collected;

screening reaction: three reactions per group were performed in parallel and the experimental procedure is shown in figure 4.

Recreening results: 75 mutants were rescreened and mutants (36) with catalytic activity 15% higher than that of the wild type were selected for final screening.

3. Final screen

(1) Mutant-induced expression

Inoculating the mutant strain obtained by re-screening into 5mL 2 XYT liquid culture medium containing kanamycin (final concentration is 50 ng/mL) at 1% inoculum size for strain activation, culturing at 37 ℃ at 210rpm for 8-9h; transferring the activated seed liquid into 100mL 2 XYT liquid culture medium containing kanamycin at 37 ℃ and 180rpm, and culturing until OD600 = 1.0; IPTG (final concentration 0.5 mM) was added, and expression was induced at 16℃overnight at 180rpm for 12-14h; the bacterial liquid was centrifuged at 8000rpm at 4℃for 10min to collect the bacterial cells.

(2) Mutant catalytic reactions

The hydrolysis reaction of the mutant whole cell to rutin is shown in figure 4.

(3) Isoquercetin was quantitatively analyzed by HPLC, the chromatographic conditions were as follows:

high performance liquid chromatograph: 1525/2487 high performance liquid chromatography system (Waters China Co., ltd.)

Chromatographic column: hypersil OSD2-C18 chromatographic column (Dalianyite analytical instruments Co., ltd.)

Detecting substances: rutin and isoquercetin

Detection wavelength: 260nm of

Run time: 16min

Flow rate: 1mL/min

Mobile phase: 0.5% glacial acetic acid: acetonitrile=84:16

Sample loading amount: 10 mu L

(4) Preparation of HPLC mark yeast

And (3) preparing a concentration-peak area standard curve by using rutin and isoquercitrin standard substances, and calculating the substrate concentration, the product concentration and the conversion rate. Preparing rutin and isoquercitrin with methanol solution with the ratio of 0.20mM:0.00mM, 0.18mM:0.02mM, 0.16mM:0.04mM, 0.14mM:0.06mM, 0.12mM:0.08mM, 0.10mM:0.10mM, 0.08mM:0.12mM, 0.06mM:0.14mM, 0.04mM:0.16mM, 0.02mM:0.18mM, 0.00mM: after passing 0.20mM standard through 0.22 μm organic filter, HPLC was performed, and as shown in FIG. 5, the rutin standard curve was y=9.1 x, and the isoquercitrin standard curve was y=8.2 x.

Final screening results: 17 mutants with catalytic activity higher than that of the wild type 10% are selected, and sequences thereof are obtained through sequencing, so that excellent mutants F44D (the coding genes are shown as SEQ ID NO. 2) and F44S (the coding genes are shown as SEQ ID NO. 3) of the alpha-L-rhamnosidase BtRha78A are obtained. The conversion rate of rutin and isoquercetin is calculated by using standard yeast of FIG. 5, and as shown in FIG. 6, the conversion rates of WT, F44A, F D and F44S are 33.9%, 54.0%, 67.0%, 79.7%, respectively, and the conversion rates of F44A, F D and F44S are increased by more than 20%, wherein the conversion rates of F44S and F44D are 45.8% and 33.1%, respectively.

Example 3: reaction time curve of excellent mutant (F44D and F44S) on rutin catalytic activity

1. Expression and purification of BtRha78A wild type and its mutants:

(1) Expression of BtRha78A wild type and its mutant was performed in the same manner as in the heterologous expression step of example 2;

(2) The collected bacterial sludge is resuspended at pH 8.0 50mM PB buffer at 1:12 (w/v), then sonicated for 50min and centrifuged at 13000rpm for 30min, and the supernatant is collected for nickel column affinity purification;

(3) The affinity purification steps are as follows:

TABLE 4 affinity purification procedure

In a chromatography cabinet at 4 ℃, the target protein after affinity purification is dialyzed twice by 2L of phosphate buffer solution with pH of 8.0 mM, then split charging is carried out in an Eppendorf tube, the protein concentration is measured by using an ultra-micro ultraviolet visible spectrophotometer Nanodrop 2000, the purity of the target protein is detected by SDS-PAGE electrophoresis, and the target protein is stored in a refrigerator at-20 ℃.

(4) The purity of the target protein is detected by SDS-PAGE electrophoresis, the electrophoresis result is shown in figure 7, the size of 4 proteins is consistent with the size of theoretical molecular weight, and the purity is more than 95%.

2. Influence of BtRha78A wild type and mutant thereof on rutin catalytic activity under different reaction time

And (3) measuring a reaction time curve of the high-activity mutant enzymatic hydrolysis rutin: the hydrolysis reaction process refers to the catalytic reaction of the example 2, the bacterial suspension is replaced by 1mg/mL pure enzyme solution, and the catalytic activity of the wild type and the mutant to rutin is measured within 0-80min at different time, and three reactions are parallel in each group.

The reaction time curve of the high-activity mutant hydrolyzed rutin under the pure enzyme condition is shown in figure 8, and the conversion rate of the wild type and the mutant shows an ascending trend along with the increase of the reaction time within 0-80 min.

Under the pure enzyme condition, as shown in FIG. 9, the conversion rate of WT was only 10.7% at 20min, and the conversion rates of F44S and F44D were increased by 2.55-fold and 1.38-fold, respectively.

To sum up: according to the invention, the alpha-L rhamnosidase BtRha78A is subjected to molecular transformation, the amino acid at the inlet of a substrate channel is subjected to semi-rational design, and excellent mutants with short reaction time and high catalytic efficiency are obtained through high-throughput screening. The natural flavone diglycosides rutin derived from the cheap raw materials of tartary buckwheat and pagodatree flower is biologically converted, so that the rare flavone glucoside isoquercetin with high physiological efficacy and high bioavailability is efficiently prepared, and a foundation is laid for industrial production and application of the isoquercetin.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims (7)

1. The alpha-L-rhamnosidase BtRha78A mutant is characterized in that the amino acid sequence of the mutant has one amino acid mutation with the BtRha78A enzyme shown in SEQ ID NO.1, and the mutation is that phenylalanine at 44 th position is mutated into aspartic acid or serine.

2. A DNA molecule encoding the α -L-rhamnosidase BtRha78A mutant of claim 1.

3. The DNA molecule of claim 2, having any one of the nucleotide sequences a1-a 3:

a1, SEQ ID NO.2 or SEQ ID NO. 3;

complementary sequences of the nucleotide sequences in a 2and a 1;

a3, a nucleotide sequence encoding said α -L-rhamnosidase BtRha78A mutant, and which differs from a1 and a2 due to the degeneracy of the genetic code.

4. A recombinant expression vector having the DNA molecule of claim 3.

5. An engineered bacterium of escherichia coli comprising the recombinant expression vector of claim 4.

6. The method for preparing the alpha-L-rhamnosidase BtRha78A mutant according to claim 1, which is characterized by comprising the following steps: inducing the escherichia coli engineering bacteria to express the alpha-L-rhamnosidase BtRha78A mutant, and separating and purifying the expressed alpha-L-rhamnosidase BtRha78A mutant.

7. The use of the α -L-rhamnosidase BtRha78A mutant of claim 1 in the preparation of isoquercetin by catalyzing rutin.

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