CN110684092B

CN110684092B - Antibacterial peptide and application thereof

Info

Publication number: CN110684092B
Application number: CN201911209415.9A
Authority: CN
Inventors: 封德顺; 杨艳琳; 杨宝谊; 王洪刚
Original assignee: Shandong Agricultural University
Current assignee: Shandong Agricultural University
Priority date: 2019-06-10
Filing date: 2019-12-01
Publication date: 2021-11-05
Anticipated expiration: 2039-12-01
Also published as: CN110684092A

Abstract

The invention discloses an antibacterial peptide and application thereof, wherein an antibacterial peptide gene is obtained by combining leaf transcriptome data induced by erysiphe trititrigia SN6306 powdery mildew with a bioinformatics method, target protein is expressed by transforming escherichia coli, and the antifungal activity of the antibacterial peptide is verified by methods such as a PDA plate test, wheat leaf smearing and the like. The antibacterial peptide can be used for preparing an inhibitor for resisting fusarium graminearum and wheat powdery mildew, and is a raw material of an antifungal inhibitor with great potential utilization value. The antibacterial peptide provided by the patent can replace the traditional chemical pesticide and prevent and treat fungal diseases of wheat and other crops.

Description

Antibacterial peptide and application thereof

Technical Field

The invention belongs to the field of molecular biology, and particularly relates to an antibacterial peptide and application thereof.

Background

Wheat is one of the important crops in China and is mainly used as a grain crop. Wheat scab and wheat powdery mildew are important diseases which seriously affect the yield and quality of wheat in Huang-Huai-Hai wheat areas. The current mainstream control measures are mainly chemical control. The application of pesticides increases environmental pollution and easily causes drug resistance of pathogenic bacteria. Antibacterial peptides are small molecule peptides that have inhibitory and killing effects on bacteria and fungi in organisms, and are components of natural defense systems for resisting pathogen invasion in many organisms, and due to their special mechanism of action, they can rapidly sterilize bacteria without easily causing drug resistance, and have broad-spectrum resistance to plant pathogens, and they become a natural drug with great development potential (Yanxianli et al, 2017).

Biological activities of antimicrobial peptides include antibacterial, antifungal and modulating immune function.

Most of the antimicrobial peptides can inhibit gram-positive bacteria and gram-negative bacteria, and the antimicrobial activities of different types of antimicrobial peptides from different sources are slightly different. Most currently considered antibacterial mechanisms are the interaction of antibacterial peptides with bacterial cell membranes (Bechinger B, Gorr SU. antibacterial peptides, Journal of fractional Research, 2017, 96(3): 254.; Tossi A, Scocchi M, Zahariev S, et al, Use of non-Amino acids to protocol structures-activity reactions and mode-of-action of antibacterial peptides, Unnatura Amino acids, Humana Press, 2012: 169-) 183). Positively charged cationic Antimicrobial peptides generate static electricity with negatively charged surface molecular membrane phospholipids of gram-negative bacteria, bind to the bacterial cell membrane, and then hydrophobic segments of the Antimicrobial peptides cause changes in membrane structure (Agents JM, S. nchez-Perrez, A, Calo-Mata P, Villa TG. Antimicrobial peptides (AMPs): antibiotic compounds which present novel proteins in the light acquisition bacteria, Biochemical Pharmacology, 2017, 133: 117-.

With the increasing problem of resistance of microorganisms to traditional antibiotics, there is increasing interest in the potential of antifungal peptides as novel antibiotics (Epand RM, Vogel HJ. Diversity of antibiotic peptides and microorganisms of action, Biochimica et Biophysica Acta-biomembranaes, 1999, 1462(1-2): 11-28). Antifungal peptides (AFP) are a subset of antibacterial peptides (AMPs), AFP can be divided into linear peptides, peptides forming amphipathic hydrophobic helices, β -sheet peptides, α -helix and β -sheet mixed peptides, peptides rich in specific amino acids, and modified cyclic peptides and Lipopeptides (Nguyen LT, Handey EF, Vogel HJ. the expansion scope of Antimicrobial peptide structures and the peptide of action. Trends in Biotechnology, 2011, 29, (9): 464-472; Tam JP, Wan S, Wong KH, Tan WL. Antimicrobial peptides, 2015-8551. biological agents, 711 (4): 757; Hampty IW.: Lipofen. Biochemical) and peptides belonging to biological peptides, Across, 8551. Fukum et al. The current resistance mechanism of antibacterial peptides to fungi is mainly based on 3 hypotheses: firstly, the antibacterial peptide inhibits the synthesis of important components of cell walls such as chitin, glucan and the like and prevents the formation of fungal cell walls; secondly, the antibacterial peptide interacts with the cell membrane to destroy the cell membrane and cause the contents to leak; thirdly, the antibacterial peptide acts on the fungal organelles such as mitochondria and the like, and finally the purpose of inhibiting and killing fungi is achieved.

The antibacterial peptide not only has antibacterial effect, but also can regulate immune system, such as chemotaxis, activate immune cells and regulate inflammation. The antibacterial peptide fowlicidin-1(6-26) has strong abilities to regulate Immune system, directly recruit neutrophils, activate macrophages, and enhance antigen-specific adaptive Immune response, and by injecting the peptide into peritoneum of mice, neutrophils were found to be specifically chemotactic, and fowl-1 (6-26) enhanced the general tendency of antigen-specific Immune response after co-administration with ovalbumin, indicating the utility of fowl-1 (6-26) as a vaccine adjuvant (Bommineni YR, Pham GH, Sunkara LT, Achata M, Zhang G. Immune regulatory activity of vaccine adjuvant of fowlicidin-1, a cathelidin host defect peptide. Molecular Immunology 2014, 59(1): 55-63).

In the long-term disease-resistant evolution process of wheat and wild kindred plants, abundant antibacterial peptide genes are generated in the genome, the novel antibacterial peptide is excavated by utilizing the bioinformatics and the molecular cell biology technology, and the efficient novel antibacterial peptide for resisting plant diseases is searched, so that the important practical value is achieved.

Disclosure of Invention

Most of the reported antibacterial peptides can destroy membrane structures, inhibit gram-positive bacteria and gram-negative bacteria, promote immunity and eliminate infection, and protect hosts from pathogenic attack. The antibacterial peptide has wide sources and is found in animals, plants and microorganisms, but the research reports of the antibacterial peptide for resisting wheat powdery mildew and gibberellic disease are less at present.

According to the application, an antibacterial peptide gene, namely Y2944, is obtained by combining transcriptome data of triticale SN6306 with a bioinformatics method, and the antifungal activity of the antibacterial peptide is verified respectively by converting escherichia coli to express a target protein and by PDA plate verification, wheat leaf smearing and other methods. The antibacterial peptide provided by the patent can replace the traditional chemical pesticide and prevent and treat fungal diseases of wheat and other crops.

The invention is realized by the following technical scheme:

the invention provides an antibacterial peptide, and the amino acid sequence of the antibacterial peptide is shown in a sequence table SEQ ID No.2.

The cDNA sequence of the antibacterial peptide gene provided by the invention is shown in a sequence table SEQ ID No.1.

The antibacterial peptide provided by the invention can be used for preparing antifungal inhibitors.

The antibacterial peptide provided by the invention can be used for preparing an inhibitor for resisting fusarium graminearum.

The antibacterial peptide provided by the invention can be used for preparing an inhibitor for resisting wheat powdery mildew.

The invention has the beneficial effects that: the invention provides a novel antibacterial peptide which can be used for preparing an inhibitor for resisting fusarium graminearum and wheat powdery mildew and is a raw material of an antifungal inhibitor with great potential utilization value.

Drawings

FIG. 1 shows the cDNA sequence and the encoded amino acid sequence of the Y2944 gene.

FIG. 2 is a signal peptide analysis of the amino acid sequence of the Y2944 protein.

FIG. 3 is a prediction of transmembrane helices of the signal peptide-removed Y2944 protein.

FIG. 4 is a 12% SDS-PAGE analysis of the expression of the tag protein in pET-32a (+) empty vector; wherein: m, premixed protein marker (wide); 1, no induction control; 2, inducing overnight; 3, precipitation after ultrasonic crushing; 4, supernatant after ultrasonication; 5-7, cleaning liquid in the purification process; 8, purified protein of interest; 9, the enzyme-cut target protein.

FIG. 5 shows the expression of the recombinant protein Y2944 in 12% SDS-PAGE; wherein: m, premixed protein marker (wide); 1, no induction control; 2, inducing overnight; 3, precipitation after ultrasonic crushing; 4, supernatant after ultrasonication; 5-7, cleaning liquid in the purification process; 8, purified protein of interest; 9, the enzyme-cut target protein.

FIG. 6 is a standard curve for protein quantification.

FIG. 7 shows the Western Blot for detecting the expression of pET-32a (+) tag protein and Y2944 protein; wherein: m, Blue Plus II Protein Marker (14-120 kDa); 1, pET-32a (+) tag protein; 2, cutting enzyme-digested pET-32a (+) tag protein; 3, Y2944 recombinant protein; 4, after the recombinant protein Y2944 is enzyme-cut; 5, Y5468 recombinant protein; 6, carrying out enzyme digestion on the Y5468 recombinant protein; 7, W662 recombinant protein; 8, after the W662 recombinant protein is cut by enzyme.

FIG. 8 is a graph of protein inhibition of Fusarium graminearum hyphae expansion; wherein A: adding empty carrier label protein; b: y2944 protein is added; c, adding Y5468 protein.

FIG. 9 is a statistical graph of the diameter of fusarium graminearum hyphae growth.

FIG. 10 is a graph of wheat leaves infected with Fusarium graminearum, in which A pET-32a (+) tag protein is added; b, adding Y2944 protein; c, adding Y5468 protein; and D, adding the W662 protein.

FIG. 11 is a graph showing the statistics of leaf length in the area of gibberellic disease infection on wheat leaves.

FIG. 12 shows powdery mildew infection YN15 wheat leaves, wherein A is coated with pET-32a (+) tag protein; b, coating Y2944 protein; c, coating Y5468 protein D and coating W662 protein.

FIG. 13 is a statistical ratio of powdery mildew-susceptible area on wheat leaves to the total area of leaves.

FIG. 14 shows the distribution of powdery mildew hyphae after staining leaves, wherein A is leaves coated with pET-32a (+) tag protein; b, leaves coated with Y2944 protein, C, leaves coated with Y5468 protein and D, leaves coated with W662 protein.

Detailed Description

Example 1 discovery of antimicrobial peptides Using bioinformatic analysis method

Comparing the existing antibacterial peptide data in an antibacterial peptide database APD (http:// APs. unmac. edu/AP/main. php) with sequencing data of leaf transcriptome of elytrigia repens SN6306 leaf which is induced by powdery mildew and has been completed in the subject group, analyzing the sequence of the antibacterial peptide coding gene in wheat, and mining 1 antibacterial peptide gene, namely 1 antibacterial peptide gene in the transcriptome dataY2944. Analyze and prepareY2944The gene sequence and amino acid sequence of (c) and the primary structure (https:// web. expasy. org/protparam /) and secondary structure (https:// npsa-prabi. ibcp. fr/cgi-bin/npsa _ Automat. plpage = npsa _ sopma. html), signal peptide (http:// www.cbs.dtu.dk/services/SignalP /) and transmembrane of the Y2944 protein were analyzedHelix (http:// www.cbs.dtu.dk/services/TMHMM-2.0 /), etc.

Y2944The gene is a novel antibacterial peptide gene found in a comparison result of an existing antibacterial peptide sequence of an APD website and sequencing data of a leaf transcriptome of the elytrigia repens SN6306 induced by erysiphe necator, the total length of cDNA is respectively 318bp, and the number of coded amino acids is respectively 105 (figure 1). The Y2944 protein has a signal peptide, and the cleavage site of the signal peptide is between 26 th and 27 th amino acids. The alignment result on the URGI of the wheat database shows that the Y2944 gene is positioned on the 6D chromosome, and Y2944 has no conserved structural domain. Through the ProtParam and SOPMA websites, the isoelectric point, molecular weight, hydrophobicity and fat coefficient of the protein, alpha-helix, beta-fold, extended chain, irregular coil and the like of the protein are predicted, and the alpha-helix and irregular coil account for a larger proportion of the protein (Table 1). The protein was shown to contain a Signal peptide according to predictions at the site of Signal P4.1 (FIG. 2). The protein topology is predicted by TMHMM 2.0 website, and the protein after removing the signal peptide is positioned outside the cell, so the Y2944 protein is probably a secreted protein (FIG. 3).

TABLE 1 structural analysis of the Y2944 protein

Example 2 verification of antibacterial function of antibacterial peptide

Method No.1

Construction of No.1.1 antibacterial peptide prokaryotic expression vector, transfer into expression strain

And (3) carrying out signal peptide prediction on a Y2944 gene sequence mined from the elytrigia repens SN6306 transcriptome data, and removing the sequence of the signal peptide. Carrying out codon optimization on Y2944 according to the codon expression preference of escherichia coli, wherein two ends of the sequence are respectively added withNcoI cleavage sites andEcoRI enzyme cutting sites, which are subjected to gene synthesis by Jinan Boshang biotechnology limited and used for the preparation of the recombinant human immunodeficiency virus (DNA)NcoI andEcoRI is the cloning site linked to the vector pET-32a (+).

The constructed pET-32a (+) plasmid was transformed into competent cells of the expression strain BL21 (DE 3) plysS.

(1) Conversion by heat shock methodE. coliBL21 (DE 3) plysS competent cell

1) Take 50. mu.L of competent cells stored in a refrigerator at-80 deg.C, add 10. mu.L of recombinant plasmid DNA, mix well quickly, ice-wash for 30min (in clean bench).

2) And (5) finishing the ice bath, thermally exciting the mixture in a metal bath at 42 ℃ for 90s, and quickly placing the mixture on ice for 1-2 min.

3) And adding 800 mu L of LB liquid culture medium into the reaction tube filled with the mixture, uniformly mixing, and incubating for 40-60 min in a constant temperature shaking table at 200rpm and 37 ℃.

4) The reaction tube was centrifuged at 12000 Xg in a centrifuge for a short time, 600. mu.L of the supernatant was aspirated, the remaining portion was resuspended and dropped onto LB solid medium containing the corresponding antibiotic, and the transformed bacteria were spread evenly onto agar plates using a sterile spreading rod. (operating in clean bench)

5) The plate is placed for 15-30 min in the forward direction and placed in a constant temperature incubator at 37 ℃ for inverted culture for 16 h.

(2) Picking single colony

Single colonies on the plates were picked and added to 5mL of LB liquid medium containing the corresponding antibiotic, mixed well, and cultured with shaking at 37 ℃ with a constant temperature shaker at 200rpm for 16 h. And after the culture is finished, preserving the bacteria and taking part of the bacteria liquid for sequencing verification.

Inducible expression of No.1.2 antibacterial peptide protein

(1) BL21 (DE 3) containing the pET-32a (+) plasmid and BL21 (DE 3) plysS containing the pET-2944 plasmid were added to 30mL of an autoinduction medium containing 100mg/mL of ampicillin at a volume ratio of 5%, and the mixture was shaken at 200rpm for 5 hours in a 37 ℃ incubator, and then the temperature of the shaker was adjusted to 25 ℃ and further at 200rpm for 10 to 16 hours.

(2) SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) detection of induced protein expression

1) Glue preparation

TABLE 2 compounding ingredients Table

2) Sample processing

13000 Xg of 1mL of induced bacterial liquid is taken, centrifuged for 10min, the supernatant is discarded, and 100 uL of protein extracting solution is added for resuspension. The centrifuge tube was placed in a metal bath at 95 ℃ for 30 min.

3) SDS-PAGE electrophoresis

10uL of the heated sample was spotted and SDS-PAGE was started.

Electrophoresis conditions: starting voltage 110V, setting the voltage as 120V after electrophoresis for 30-40 min, continuing electrophoresis for 100-120 min until a Coomassie brilliant blue indicator strip in a lane moves to a position 1cm away from the bottom of the separation gel, and stopping electrophoresis.

4) Gel imaging

The gel staining was performed according to the procedures described in the Coomassie brilliant blue protein gel fast staining solution (Beijing Solebao science Co., Ltd.).

The using method comprises the following steps:

and (3) preparing a working solution, namely adding 100mL of the solution B into 2mL of the solution A, and uniformly mixing to obtain the working solution.

1. The PAGE gel after electrophoresis (size 8 cm. times.10 cm for example) was removed and placed in a container, 50mL of deionized water was added, heating was stopped after boiling, shaking was continued on a decolorization shaker for 5 minutes, and the aqueous solution was discarded.

2. Adding 25mL of quick dyeing working solution, heating to boil, keeping the boiling state for 30-60 s, stopping heating, continuing to shake on a decoloring shaking table for 5-10 min, and discarding the dyeing solution.

3. And adding about 50mL of deionized water, heating to boil, keeping the boiling state for 30-60 s, stopping heating, continuing to shake on a decoloring bed for 5-10 min, and changing water to finish decoloring, wherein the result is observed.

Note that:

1. in the cleaning step before dyeing, the quality of water is very important, the better the quality is, the higher the sensitivity is, and researches prove that if the water is used for heating and cleaning, the dyeing effect and the sensitivity are only the same as those of the conventional methanol Coomassie brilliant blue dyeing.

2. The decolorization can be carried out by washing with tap water.

3. If a background-free dyed gel is to be obtained, the decolorization step can be repeated or the gel can be left in water overnight.

4. The degree of shrinkage and expansion of the PAGE gel dyed by the product is less than 5%, and the dyed gel can be placed in water for several months without obvious decolorization.

5. After each heating, the dyeing effect can be enhanced by further shaking on the decolorizing shaking table for 5 min.

6. The dyeing liquid is slightly corrosive and needs to be handled with gloves. The stained gel was photographed using a gel imaging system and the results were observed.

No.1.3 antimicrobial peptide protein purification

No.1.3.1 antimicrobial peptide protein purification

According to Beaver Beads^TMThe Protein Purification is carried out according to the instruction on the His-tag Protein Purification kit, and the operation flow is as follows:

(1) magnetic bead pretreatment:

1) and (3) putting the beaver magnetic bead product on a vortex mixer for fully mixing, taking 5mL of magnetic bead suspension in a 15mL centrifuge tube by using a pipettor, carrying out magnetic separation, discarding supernatant, and taking the centrifuge tube from the magnetic separator.

2) Adding 5mL Binding Buffer into the centrifuge tube filled with the magnetic beads, and turning the centrifuge tube up and down for several times to resuspend the magnetic beads; magnetic separation was performed and the supernatant removed. The washing was repeated 2 times. (Note: in the magnetic separation process, in order to reduce the loss of the magnetic beads in the use process, after the solution becomes clear, the cover of the centrifugal tube is tightly covered, the centrifugal tube is kept still on the magnetic separator, the magnetic separator and the centrifugal tube are held to be turned over for a plurality of times up and down, so that the clear solution washes the residual magnetic beads on the cover of the centrifugal tube, the solution is kept still for a moment to become clear again, the same is as follows.)

(2) Binding of target protein to magnetic beads

1) Suspending 2g of wet-weight thallus by using 10mL Binding Buffer, crushing and cracking to obtain a target crude protein sample, adding the target crude protein sample into a centrifugal tube filled with pretreated magnetic beads, and placing the centrifugal tube in a vortex mixer for oscillation for 15 s.

2) And (3) placing the centrifugal tube on a rotary mixer, and carrying out rotary mixing at room temperature for 20-30 min (if necessary, under the low-temperature environment of 2-8 ℃, the rotary mixing can be carried out for 1h to prevent the target protein from being degraded).

3) And (3) placing the centrifugal tube on a magnetic separator for magnetic separation, removing the supernatant into a new centrifugal tube for subsequent detection, and taking the centrifugal tube off the magnetic separator for subsequent washing.

(3) Magnetic bead washing

1) Adding 10mL Washing Buffer into a centrifuge tube filled with magnetic beads, slightly overturning the centrifuge tube for several times to resuspend the magnetic beads, magnetically separating, and removing the cleaning solution into a new centrifuge tube for sampling detection. This step was repeated 1 time.

2) Adding 10mL Washing Buffer into a centrifugal tube filled with magnetic beads, resuspending the magnetic beads, transferring the magnetic bead suspension into a new centrifugal tube (preventing nonspecific adsorption protein on the wall of the original centrifugal tube from polluting target protein), carrying out magnetic separation, and removing supernatant to a cleaning solution collecting tube.

(4) Elution of target protein

1) The user can change the Elution volume as required to adjust the concentration of the target protein, 2-10 mL of Elution Buffer is added, the centrifuge tube is turned over slightly for several times to suspend the magnetic beads, the magnetic separation is carried out, and the eluent is collected into a new centrifuge tube, namely the purified target protein sample.

2) If necessary, the above steps can be repeated for 1 time, and the sample is collected into a new centrifugal tube to detect whether the target protein is completely eluted.

(5) Magnetic bead post-treatment

1) Adding 5mL of Elution Buffer into a centrifuge tube filled with magnetic beads, turning the centrifuge tube up and down for several times to suspend the magnetic beads, carrying out magnetic separation, and removing supernatant.

2) Repeat the above step 2 times.

3) Add 5mL ddH to centrifuge tube₂And O, overturning the centrifugal tube for several times up and down to suspend the magnetic beads, performing magnetic separation, and removing supernatant.

4) Repeat the above step 2 times.

5) Adding Storage Buffer into magnetic beads to make the total volume 5mL, storing at 2-30 deg.C (long-term Storage, standing at 2-8 deg.C), and allowing for next purification of the same protein.

(6) Regeneration of magnetic beads

When the magnetic beads are used three or more times in succession, the ability to bind to the target protein may be significantly reduced, and a magnetic bead regeneration treatment is recommended. The magnetic bead regeneration operation will be described in detail with respect to 5mL of a 10% (v/v) magnetic bead suspension:

1) performing magnetic separation on the magnetic bead suspension, removing supernatant, taking down a centrifuge tube from the magnetic separator, and adding 5mL ddH into the centrifuge tube₂And O, turning the centrifugal tube up and down for several times to resuspend the magnetic beads, magnetically separating and removing supernatant.

2) Adding 5mL striping Buffer, turning the centrifuge tube up and down for several times to resuspend the magnetic beads, mixing by rotation at room temperature for 5min, performing magnetic separation, and removing the supernatant. This step was repeated 1 time.

3) Add 5mL ddH₂And O, turning the centrifugal tube up and down for several times to resuspend the magnetic beads, magnetically separating, removing supernatant, and repeating the step for 2 times.

4) Alkali treatment: adding 5mL of Beads Washing Buffer, turning the centrifuge tube up and down for several times to resuspend the magnetic Beads, mixing by rotation at room temperature for 5min, performing magnetic separation, and removing the supernatant. Add 5mL ddH₂And O, turning the centrifugal tube up and down for several times to resuspend the magnetic beads, magnetically separating and removing supernatant. Repeating ddH₂And O washing for 3-5 times until the washing liquid is neutral.

5) Adding 5mL of Recharge Buffer, turning the centrifuge tube up and down for several times to resuspend the magnetic beads, rotating and mixing for 20min at room temperature, performing magnetic separation, and removing supernatant.

6) Add 5mL ddH₂And O, turning the centrifugal tube up and down for several times to resuspend the magnetic beads, magnetically separating and removing supernatant. The step is repeated for more than 4 times to ensure that the nickel ions are completely removed.

7) A Storage Buffer was added to the beads to make a total volume of 5mL, and the beads were stored at 2-30 deg.C (for long term Storage, at 2-8 deg.C).

(7) SDS-PAGE gel electrophoresis detects the protein purification condition, and Coomassie brilliant blue protein gel rapid staining solution is used for staining the gel and observing the result.

No.1.3.2 antimicrobial peptide protein dialysis

And (3) putting the dialysis bag containing the purified protein into 33mM sodium phosphate solution, putting the dialysis bag on a magnetic stirrer at 4 ℃ for dialysis, and replacing the dialysate every 4 hours for 24 hours. The dialyzed protein was dispensed into 2mL centrifuge tubes and stored in a freezer at-80 ℃.

Determination of No.1.3.3 concentration of antimicrobial peptide protein

Protein concentration was measured according to the protocol of the simple protein quantification kit (Bradford) instructions as follows:

(1) preparing a protein standard solution

The protein standard solution was diluted to a final concentration of 0.22 mg/ml. The protein standard should be diluted with the same solution as the protein sample to be tested.

(2) Protein quantification

Protein quantification was performed according to Easy Protein quantitafar Kit (Bradford) Kit instructions.

Bovine Serum Albumin (BSA) standard solution (0.22 mg/mL) was diluted as follows

TABLE 3 dilution of Bovine Serum Albumin (BSA) standard solution

Adding standard samples of various volumes into an enzyme label plate, supplementing the standard samples to 20 mu L with sterile water, adding 200 mu L of Coomassie brilliant blue dye solution, standing at room temperature for 10-20 min, measuring the light absorption value of each sample at 595nm by using an enzyme label instrument, recording the reading, and repeating the operation for 3 times to ensure the accuracy of the data. The absorbance of the sample without BSA was used as a blank to plot a standard curve for protein concentration. Protein concentrations were calculated as described above, and if the protein concentration obtained was not within the standard curve, it was recommended to dilute the sample for re-determination.

Note that:

coomassie brilliant blue G-250 strongly binds to quartz cuvettes, glass or plastic cuvettes can be used;

the protein concentration is measured from low to high, the cuvette is not required to be repeatedly cleaned, and the water quality can influence the measurement result;

the light absorption value within 5-20 min of reaction is most stable, the reaction time of each tube is kept consistent, and the measurement is preferably carried out within the same time, so that the reading is accurate;

the standard curve can be divided into 2-3 groups for parallel operation, so as to obtain more accurate results.

No.1.3.4 Western Blot assay

(1) Sampling 5ul of samples, sequentially loading the samples, performing SDS-PAGE electrophoresis, running the concentrated gel for 30min at 100V, and running the concentrated gel at 120V until the electrophoresis is finished after the samples enter the separation gel.

(2) Soaking the PVDF membrane in 100% methanol for 30 s; placing the sponge, the filter paper, the gel, the PVDF membrane, the filter paper and the sponge in a membrane transferring groove from a negative electrode to a positive electrode in sequence, and pouring a membrane transferring buffer solution; the membrane is rotated for 2h under the voltage of 200V and the constant current is 150 mA.

(3) After the membrane transfer was completed, the PVDF membrane was washed 3 times for 5min in 1 XTSST buffer.

(4) The PVDF membrane is placed in a sealing solution containing 5% of skimmed milk powder and sealed for 1h at room temperature.

(5) Taking out the PVDF membrane from the confining liquid, and putting the PVDF membrane into a 1 xTBST buffer solution for washing for 3 times, 5min each time; primary antibody (His, 1: 2000) was diluted with blocking solution, and the membrane was placed in the primary antibody dilution and incubated for 2h at 4 ℃ on a shaker.

(6) Taking out the PVDF membrane from the primary antibody, and washing in 1 × TBST buffer solution for 3 times, 5min each time; diluting the secondary antibody (goat anti-mouse, 1: 1000) with blocking solution containing 5% skimmed milk powder; the membrane was placed in a secondary antibody diluent and incubated for 1h on a shaker at room temperature.

(7) The PVDF membrane was removed and washed 3 times for 5min in 1 XTSST buffer.

(8) Mixing solution A and solution B of ECL developing solution according to the ratio of 1:1 to make the film fully contact with the developer.

(9) And (5) gel imaging analysis.

Functional analysis of No. 1.3.5Y 2944 protein for inhibiting fungi

Effect of No.1.3.5.1 protein on Fusarium graminearum hypha development

(1) PDA plate method for verifying influence of Y2944 protein on development of fusarium graminearum hyphae

1) Induction of protein expression

The procedure was the same as in the previous experiment.

2) SDS-PAGE electrophoresis detection of protein expression

The procedure was the same as in the previous experiment.

3) Ultrasonic cell disruption

Centrifuging, removing supernatant, collecting overnight induced Escherichia coli, adding 1g wet weight of thallus into 5mL sterile water, resuspending thallus, and ultrasonically breaking cells at 50W of maximum power, 5s of breaking time and 3s of intermittent time under low temperature condition until the thallus is clear and not sticky. The crude protein supernatant was collected by centrifugation and stored in a freezer at-20 ℃.

4) Protein quantification

Crude protein was quantified according to the method of 2.6.4.3 (2).

5) PDA plate verification of influence of Y2944 protein on development of fusarium graminearum hyphae

Adding 200 mu L of crude protein (crude protein concentration: 471-540 mu g/mL) into 25mL of culture medium, adding the melted PDA culture medium into the crude protein supernatant of pET-32a (+), Y2944, mixing uniformly, and then pouring the plate. After the culture medium is solidified, a fusarium graminearum cake with the diameter of 8mm is placed in the center of the culture medium and is inversely cultured at the temperature of 25 ℃. This experimental set-up was repeated 3 times.

(2) In-vitro leaf inoculation method for verifying influence of Y2944 protein on development of fusarium graminearum hyphae

The method refers to Condon et al (2016), selecting several wheat leaves with one leaf and one core, cutting off the middle part of the leaf with length of 5cm, and making the diameter of 1mm in the middle of the upper surface of the leaf with a puncher or pipette tip²Of the wound is circular. Protein prepared from 5 mu L of crude protein and 1 mu L of fusarium graminearum conidium liquidThe spore mixture was dropped onto a round wound in the center of the leaf. The two ends of the blade are inserted into the moisture-preserving identification plate, so that the blade is arched and stands on the identification plate, and the circular hole is positioned at the top of the arch. Finally, the plate was incubated in a 25 ℃ incubator for 3 days. After the culture, the bacterial infection of the circular hole part is observed, and the resistance of the protein to the gibberellic disease is analyzed.

Influence of No.1.3.5.2 protein on wheat leaf infection by Erysiphe graminis

(1) Coating YN15 (Ninong 15) wheat leaf with purified target protein

A5 cm part of the YN15 wheat leaf blade which is one leaf and one heart is selected, and the area is marked by a mark pen. Taking a part of purified target protein which is stored at the temperature of 80 ℃ below zero after being purified, carrying out enzyme digestion by enterokinase (the enzyme digestion condition is that every 300 mu L of purified protein with the concentration of 241-252 mu g/mL is added with 0.06U of recombinant enterokinase, and the enzyme digestion is carried out for 16 hours in a metal bath at the temperature of 25 ℃), adding Tween with the final concentration of 0.025%, evenly mixing, dipping the protein by a cotton swab on a leaf marking area, and uniformly coating the front surface and the back surface of a leaf. Multiple replicates were made for each protein. Placing the applied YN15 wheat in an incubator at 23 ℃ and under 16h/d of light.

(2) Photoshop software-based YN15 wheat leaf infection analysis

Refer to the method of Lianyui et al (2016). And according to the fact that the ratio of the powdery mildew area to the normal green leaf area is equal to the pixel ratio of the powdery mildew area to the normal green leaf area, shooting an image of YN15 wheat leaves after 5d of protein coating by a mobile phone, and respectively obtaining pixels of the powdery mildew area and the normal green leaf area and the sum of the pixels of the powdery mildew area and the normal green leaf area on Photoshop software, namely total pixels of the leaves. And analyzing the influence of the protein on the wheat leaves infected by the powdery mildew by comparing the ratio of the pixels of the powdery mildew infection area to the total pixels of the leaves.

(3) YN15 wheat leaf infection condition observed under microscope

1) Decolorizing and dyeing YN15 wheat leaf

Soaking the wheat leaves to be observed in a destaining solution overnight, rinsing with sterile water for 2 times, placing the wheat leaves in a staining solution for staining for 15-30 min, and repeatedly rinsing with sterile water for many times to observe the wheat leaves or storing the wheat leaves in a preserving solution for 3 days at most.

2) YN15 wheat leaf infection condition observed under microscope

And taking out the leaves to be observed, flatly paving the leaves on a glass slide, placing the glass slide on an objective table of a microscope, observing the leaves under a 4-time objective lens and taking a picture.

Test results and analysis

Expression and purification of No. 2.1Y 2944 protein

The recombinant plasmid prepared by the company is transformed into BL21 (DE 3) plysS expression strain, and after sequencing, the strain containing the recombinant plasmid with correct sequence verification is self-induced to express protein. The self-induced protein expression conditions were: the expression strain containing the recombinant plasmid grew logarithmically in the self-induction medium to OD in a constant temperature shaker at 200rpm and 37 ℃₆₀₀When the value is 0.6-1, the temperature of the oscillator is reduced to 25 ℃, and lactose enters cells to induce protein expression. After the induction expression is finished, taking part of the thalli, adding a proper amount of protein extracting solution, carrying out 12% SDS-PAGE electrophoresis, and detecting the protein expression condition. After the high expression of the target protein in the thallus supernatant is detected by preliminary electrophoresis, the thallus is collected and ultrasonically crushed, the crushed crude protein supernatant collected centrifugally is purified by beaver magnetic beads which specifically adsorb His label protein. The protein expression and purification effect were checked again by 12% SDS-PAGE electrophoresis. The molecular weights of pET-32a (+), and Y2944 target proteins are predicted to be 22kD and 25kD respectively according to DNMAN software, and the sizes of target bands in figures 4 and 5 are basically consistent with the predicted molecular weight of the proteins, which indicates that the target proteins are successfully expressed and have good purification effect. The concentrations of pET-32a (+), and Y2944 purified target proteins were 252. mu.g/mL and 241. mu.g/mL, respectively, as determined from the protein quantitative standard curve of FIG. 6, and the concentrations of pET-32a (+), and Y2944 crude proteins were 540. mu.g/mL and 504. mu.g/mL, respectively, as determined.

And (3) detecting the purified target protein and the target protein cut by enterokinase by Western blot, wherein the result shows that the size of the band is consistent with the expected size. Since the cleaved target protein and the His-tag protein are separated, the hybridization signal of the cleaved target protein cannot be displayed on the PVDF membrane, but only the hybridization signal of the His-tag protein in the former stage of the target protein (fig. 7).

Functional verification of No.2.2 protein

Effect of No.2.2.1 protein on Fusarium graminearum hypha development

(1) Protein function verification by PDA plate method

Crude protein was added to a PDA medium at a certain concentration, a cake of Fusarium graminearum with a diameter of 8mm was placed in the center of the medium, and the medium was placed upside down in an incubator at 25 ℃ for 5 days, and it was observed that Y2944 crude protein had the effect of slowing down the rate of hypha expansion of Fusarium graminearum in the center of the medium, compared with the medium to which pET-32a (+) protein was added (FIGS. 8 and 9).

(2) In vitro leaf inoculation method for verifying protein function

Mixing crude protein and fusarium graminearum conidium suspension uniformly according to a certain proportion, and dripping 2 mu L of protein spore mixed solution on a through hole in the center of a YN15 wheat leaf segment. The treated leaf was placed in an arch shape on a moisture-retaining plate and cultured in an incubator at 25 ℃ for 3 days in a closed state. As can be seen from the observation, the wheat leaves added with 2944 protein were less susceptible than the leaves added with pET-32a (+) protein (FIG. 10, FIG. 11).

Influence of No.2.2.2 protein on wheat leaf infection by powdery mildew

The purified target protein is cut by enterokinase, 0.025 percent of Tween is used as a surfactant, the purified target protein is smeared on the middle section of a leaf of YN15 wheat with one leaf and one heart, and the front side and the back side are repeatedly and evenly smeared to ensure that the protein is fully contacted with the leaf. And (4) placing the treated wheat in a constant-temperature powdery mildew incubator to inoculate powdery mildew. After 5 days, the leaves of wheat coated with Y2944 are observed to be infected with bacteria or to be slightly infected, while the leaves coated with the empty carrier protein and the areas not coated with the protein are infected with diseases, which proves that the Y2944 protein has the effect of inhibiting the wheat leaves from being infected with erysiphe necator (figure 12).

And calculating the ratio of the area pixels of the blade infected with powdery mildew to the total pixels of the blade after the protein is smeared by Photoshop software, and comparing the susceptibility degrees of the blade. It can be seen that the leaves coated with the empty carrier protein are seriously infected, the ratio of the infected area to the whole leaves reaches 13%, while the leaves coated with the Y2944 protein is only 0.29%, and the effect of inhibiting powdery mildew infection is better (figure 13).

The wheat leaves are decolorized, dyed and observed under a microscope, so that the leaves coated with the target protein are lighter in powdery mildew infection than those coated with the empty carrier protein and non-coated areas, and have less hypha. The Y2944 protein is shown to have obvious effect on inhibiting the infection of powdery mildew (figure 14).

The gene synthesis, vector construction, protein prokaryotic expression, PDA plate test and in vitro leaf test prove that the target protein can inhibit the development of fusarium graminearum hyphae and inhibit the infection of powdery mildew.

Sequence listing

<110> Shandong university of agriculture

<120> antibacterial peptide and application thereof

<160> 2

<170> SIPOSequenceListing 1.0

<210> 1

<211> 318

<212> DNA

<213> wheat (Triticum aestivum)

<400> 1

atgaagccgc agacgcagct cctcctcctc ttggcctaca tcgccgcggc gctggtcatg 60

agcggcggcg tcctcgccgg cgccggcacc catgcggcga tgccggtgcg taccgtcgag 120

gaagacgaag tgggcttcac ggagcgtgag gaggaggcgg cgtacccaca gaggagggtg 180

cttgcttaca gcccaacttc catcggctac ggagggctgg aggcgaacaa ggcggcgtgc 240

tacggctcct gccccggccg ggggcagccc tacaccggcc gcggctgcaa ggccatcttc 300

ggctgccgcg ggcgttga 318

<210> 2

<211> 105

<212> PRT

<213> wheat (Triticum aestivum)

<400> 2

Met Lys Pro Gln Thr Gln Leu Leu Leu Leu Leu Ala Tyr Ile Ala Ala

1 5 10 15

Ala Leu Val Met Ser Gly Gly Val Leu Ala Gly Ala Gly Thr His Ala

20 25 30

Ala Met Pro Val Arg Thr Val Glu Glu Asp Glu Val Gly Phe Thr Glu

35 40 45

Arg Glu Glu Glu Ala Ala Tyr Pro Gln Arg Arg Val Leu Ala Tyr Ser

50 55 60

Pro Thr Ser Ile Gly Tyr Gly Gly Leu Glu Ala Asn Lys Ala Ala Cys

65 70 75 80

Tyr Gly Ser Cys Pro Gly Arg Gly Gln Pro Tyr Thr Gly Arg Gly Cys

85 90 95

Lys Ala Ile Phe Gly Cys Arg Gly Arg

100 105

Claims

1. The application of an antibacterial peptide is characterized in that: the antibacterial peptide consists of amino acid residues 27-105 in SEQ ID NO.2, and the application is to inhibit fusarium graminearum and/or wheat powdery mildew.