WO2021258679A1 - 一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因、编码的蛋白质和应用 - Google Patents

一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因、编码的蛋白质和应用 Download PDF

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WO2021258679A1
WO2021258679A1 PCT/CN2020/137155 CN2020137155W WO2021258679A1 WO 2021258679 A1 WO2021258679 A1 WO 2021258679A1 CN 2020137155 W CN2020137155 W CN 2020137155W WO 2021258679 A1 WO2021258679 A1 WO 2021258679A1
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kunitz
protease inhibitor
serine protease
pinctada martensii
pmkupi
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PCT/CN2020/137155
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English (en)
French (fr)
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梁海鹰
何军军
申铖皓
房晓宸
卢金昭
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广东海洋大学
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Priority to ZA2022/01931A priority Critical patent/ZA202201931B/en

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/81—Protease inhibitors
    • C07K14/8107—Endopeptidase (E.C. 3.4.21-99) inhibitors
    • C07K14/811—Serine protease (E.C. 3.4.21) inhibitors
    • C07K14/8114—Kunitz type inhibitors
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
    • A61P31/00—Antiinfectives, i.e. antibiotics, antiseptics, chemotherapeutics
    • A61P31/04—Antibacterial agents
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K38/00—Medicinal preparations containing peptides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/30—Against vector-borne diseases, e.g. mosquito-borne, fly-borne, tick-borne or waterborne diseases whose impact is exacerbated by climate change

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  • the invention belongs to the technical field of genetic engineering, and in particular relates to a Kunitz type serine protease inhibitor gene, encoded protein and application of Pinctada martensii.
  • Antimicrobial peptides are the most important link in the biological immune mechanism of shellfish, and they are also the most important line of defense for shellfish against pathogen invasion. Understanding the composition and characteristics of various antimicrobial peptide molecules in Pinctada vulgaris is important for the development of sources of antimicrobial peptides in Pinctada chinensis New biological antibiotics are of great significance, but currently there are few reports on the antimicrobial peptides of Pinctada martensii, and there is no report of the antimicrobial peptide sequence of Pinctada martensii in the database.
  • the purpose of the present invention is to provide a Kunitz type serine protease inhibitor gene, encoded protein and application of Pinctada martensii.
  • the protein encoded by the gene provided by the present invention is effective against Escherichia coli, Pseudomonas aeruginosa, Aeromonas hydrophila, Vibrio parahaemolyticus and Vibrio harveyi have inhibitory effects.
  • the present invention provides a Kunitz-type serine protease inhibitor gene of Pinctada martensii, and the nucleotide sequence of the Kunitz-type serine protease inhibitor gene of Pinctada martensii is shown in SEQ ID No. 1.
  • the present invention also provides the protein encoded by the Kunitz-type serine protease inhibitor gene of Pinctada martensii according to the above technical scheme, and the amino acid sequence of the protein is shown in SEQ ID No.2.
  • the present invention also provides the application of the protein described in the above technical scheme in the preparation of drugs for inhibiting microorganisms.
  • the microorganisms include Gram-negative bacteria.
  • the gram-negative bacteria include Escherichia coli, Pseudomonas aeruginosa, Aeromonas hydrophila, Vibrio parahaemolyticus, and Vibrio harveyi.
  • the present invention provides a Kunitz-type serine protease inhibitor gene of Pinctada martensii.
  • the nucleotide sequence of the Kunitz-type serine protease inhibitor gene of Pinctada martensii is shown in SEQ ID No. 1, and the encoded protein The amino acid sequence of is shown in SEQ ID No.2.
  • the protein encoded by the gene provided by the present invention has an inhibitory effect on Escherichia coli, Pseudomonas aeruginosa, Aeromonas hydrophila, Vibrio parahaemolyticus and Vibrio harveyi.
  • Figure 1 is a schematic diagram of the cloning site of pMD19-T Vector
  • Figure 2 shows the prediction of the transmembrane domain of Pinctada martensii PmKuPI
  • Figure 3 shows the prediction of the PmKuPI domain
  • FIG. 4 shows the homology comparison of PmKuPI
  • Figure 5 shows the phylogenetic tree construction (Neighbor-joining method).
  • Figure 6 shows the expression distribution of PmKuPI gene in each tissue of Pinctada martensii, M: mantle, B: blood cells, Gi: gills, Go: gonads, A: adductor muscle, He: hepatopancreas;
  • Figure 7 shows the verification of PmKuPI prokaryotic expression recombinant plasmid
  • Figure 8 shows the induced expression of rPmKuPI (SDS-PAGE), PC1: BSA (1 ⁇ g); PC2: BSA (2 ⁇ g); M1: Marker; NC: no induced whole bacteria; 1: 15°C induced whole bacteria; 2: 37°C Induction of whole bacteria; NC1: no induction supernatant; 3: 15°C induction supernatant; 4: 37°C induction supernatant; NC2: no induction precipitation; 5: 15°C induction precipitation; 6: 37°C induction precipitation;
  • Figure 9 shows the induced expression of rPmKuPI (Western Blot), M2: Marker; NC: no induction of whole bacteria; 1: 15°C induction of whole bacteria; 2: 37°C induction of whole bacteria; NC1: no induction supernatant; 3:15 °C induced supernatant; 4: 37°C induced supernatant; NC2: no induced precipitation; 5: 15°C induced precipitation; 6: 37°C induced precipitation;
  • Figure 10 is rPmKuPI purification analysis note, A: 1: BSA (2 ⁇ g); M1: Marker; 2: Refolded target protein (2 ⁇ g); B: M2: Marker; 3: Refolded target protein;
  • Figure 11 is the determination of the antibacterial activity of rPmKuPI (E. coli).
  • Figure 12 is the determination of the antibacterial activity of rPmKuPI (Pseudomonas aeruginosa);
  • Figure 13 is the determination of the antibacterial activity of rPmKuPI (Aeromonas hydrophila);
  • Figure 14 is the determination of the antibacterial activity of rPmKuPI (Vibrio parahaemolyticus).
  • Figure 15 is the determination of the antibacterial activity of rPmKuPI (Vibrio harveyi).
  • Figure 16 shows the morphological changes of rPmKuPI acting on bacteria:
  • a and E are the PBS control groups of Pseudomonas aeruginosa and Vibrio parahaemolyticus, respectively
  • B, C, and D are the experimental groups of rPmKuPI acting on Pseudomonas aeruginosa
  • F , G and H are the experimental groups where rPmKuPI acts on Vibrio parahaemolyticus.
  • the present invention provides a Kunitz-type serine protease inhibitor gene of Pinctada martensii, and the nucleotide sequence of the Kunitz-type serine protease inhibitor gene of Pinctada martensii is shown in SEQ ID No. 1, specifically as follows:
  • the present invention also provides the protein encoded by the Kunitz-type serine protease inhibitor gene of Pinctada martensii according to the above technical scheme.
  • the amino acid sequence of the protein is shown in SEQ ID No. 2, and is specifically as follows:
  • the present invention also provides the application of the protein described in the above technical scheme in the preparation of drugs for inhibiting microorganisms.
  • the microorganisms preferably include Gram-negative bacteria, and the Gram-negative bacteria preferably include Escherichia coli, Pseudomonas aeruginosa, Aeromonas hydrophila, Vibrio parahaemolyticus and Vibrio harveyi bacteria.
  • the specific primers of PmKuPI gene are designed using Primer Premier 5.0.
  • the 5'-end and 3'-end specific primers are designed according to the principle of RACE amplification, and the full-length cDNA of the gene is obtained by comparison and splicing.
  • the primer sequence is as follows.
  • Primer Serial number Sequence use PmKuPI-3'-inner SEQ ID No. 3 CTATTCATACGACTCGGCAAGA 3'-RACE PmKuPI-3'-outer SEQ ID No. 4 CCCGAAACAGGTTCTCTACGCT 3'-RACE PmKuPI-5'-inner SEQ ID No. 5 TGTTTTCATTTCCACCGCATCC 5'-RACE PmKuPI-5'-outer SEQ ID No. 6 CAGTCTCTCTGGGCAGTAAGCATC 5'-RACE M13-F SEQ ID No. 7 CGCCAGGGTTTTCCCAGTCACGAC Colony PCR detection M13-R SEQ ID No.
  • a trace nucleic acid quantifier measures the concentration and purity of total RNA.
  • the total RNA obtained is stored in an ultra-low temperature refrigerator at -80°C for later use.
  • Reagent dose 5 ⁇ M-MLV Buffer 2.0 ⁇ L dNTP Mixture(10m M) 0.5 ⁇ L RNase Inhibitor 0.25 ⁇ L RTase M-MLV(RNase H-) 0.25 ⁇ 1 ⁇ L RNase-free water Make up to 12 ⁇ L
  • PrimeSTARHS high-fidelity enzyme amplification obtains the target fragment.
  • the PCR reaction system is as follows:
  • the purified PCR product was ligated to the pMD-19T Vector vector ( Figure 1).
  • the system is as follows:
  • Reagent dose Solution I 5 ⁇ L Destination segment 4.5 ⁇ L pMD19-T Vector 0.5 ⁇ L Total 10 ⁇ L
  • connection procedure is: connect at 16°C for about 16 hours.
  • DH5 ⁇ competent cells Take the DH5 ⁇ competent cells out of the ultra-low temperature refrigerator, place them on ice until they are slightly soluble, and then add the ligation product to a tube containing 100 ⁇ L DH5 ⁇ competent cells, gently pipetting evenly; place on ice for 30 minutes, heat shock at 42°C for 60 to 90 seconds, Place on ice for 2 to 3 minutes; then add 890 ⁇ L of LB liquid medium preheated at 37°C in advance, and culture at 37°C with 200 rpm shaking for 1 h; then at 4000 rpm for 2 minutes, discard the supernatant, leaving about 100 ⁇ L, gently blow off the suspended cells, and Coat on the LA (Amp+) solid plate; finally, incubate upright for half an hour at 37°C, then inverted for overnight incubation.
  • Nested PCR uses 3', 5'specific primers combined with universal primers (NUP and UPM) for amplification.
  • Reagent volume Premix Taq 5 ⁇ L 3′/5′cDNA template 0.4 ⁇ L
  • NCBI blastx for sequence homology and similarity analysis
  • DNAMAN 6.0 software sequence search, splicing and comparison ExPASy online prediction of its theoretical molecular weight (MW) and isoelectric point (pI); use SignalP 4.0 Server for signal peptide sequence prediction ; TMHMM Server v.2.0 analyzes the transmembrane domain of the sequence; MEGA 6 software uses the NJ method to construct a phylogenetic tree; SoftBerry Psite predicts the functional site of its deduced amino acid sequence; SOPMA predicts the protein secondary structure.
  • Tissue quantification Take 10 scallops with the same size and good vigor, and collect tissues including gonads, gills, mantle, hemolymph, adductor muscle and hepatopancreas.
  • PAMPs stimulation 320 healthy Pinctada martensii kept for 1 week and randomly divided into 4 groups: LPS stimulation group (experimental group), PGN stimulation group (experimental group), PolyI:C stimulation group (experimental group) ), PBS group (control group), 80 shells each. Adopting the method of adductor muscle injection, the experimental group was injected with 100 ⁇ L of LPS, PGN, PolyI:C (10 ⁇ g/mL) each, and 100 ⁇ L of PBS was injected as the control group. At 0, 3, 6, 12, 24, 48, 72, 96 hours after injection, 10 shellfish were randomly selected from each group to take the whole tissue for use.
  • the hemolymph was centrifuged at 4°C, 800 ⁇ g, and the supernatant was discarded.
  • Add 1mL Trizol shake gently to make the suspension uniform, extract the total RNA and reverse transcribed into cDNA for subsequent quantitative analysis (Note: PBS is sterilized, LPS, PGN, PolyI:C are prepared with sterilized PBS ; During the experiment, no bait was fed and no deaths occurred).
  • the primers used in the fluorescence quantitative PCR reaction are shown in Table 1.
  • the extraction method of total RNA is the same as steps (1) to (4) in 3.
  • RNA is combined with primers, PCR program is 70°C, 10min, placed on ice for 2 ⁇ 3min.
  • the sample addition system is as follows:
  • Reagent dose 5 ⁇ M-MLV Buffer 2.0 ⁇ L dNTP Mixture(10m M) 0.5 ⁇ L RNase Inhibitor 0.25 ⁇ L RTase M-MLV(RNase H-) 0.25 ⁇ 1 ⁇ L RNase-free water Make up to 12 ⁇ L
  • Fluorescence quantitative data was analyzed by the 2- ⁇ ct method. The test results were all expressed as mean ⁇ standard deviation, and SPSS17.0 software was used to perform one-way ANOVA, and Duncan’s multiple comparison was used to test the significance of differences in the mean.
  • Gene synthesis is performed according to the existing target gene sequence, which is used as a template for subsequent subcloning, and the restriction sites for introducing restriction enzymes are NcoI and HindIII.
  • Recombinant PmKuPI ORF amplification, PCR system 10 ⁇ L of Premix Ex Taq, 0.5 ⁇ L of synthetic template, 0.4 ⁇ L of Forward Primer and Reverse Primer, and ddH 2 O supplement system to 20 ⁇ L.
  • the procedure is: denaturation at 94°C for 5min; 98°C for 10s, 55°C for 30s, 72°C for 60s, 30 cycles.
  • the reaction products were detected by gel electrophoresis.
  • Plasmid extraction refers to the instructions of the Easy Pure Plasmid Mini Prep Kit Silica Gel Membrane Spin Column Plasmid DNA Mini Extraction Kit.
  • Double digestion of the empty plasmid pET-28a(+) and the extracted recombinant plasmid with MluI, XhoI and HindIII endonucleases The system is 5.0 ⁇ L of 10 ⁇ FD Buffer, MluI endonuclease 3.0 ⁇ L, 20 ⁇ L of plasmid, and ddH 2 O to make up the system to 50 ⁇ L. Mix gently, and incubate at 37°C for 2h.
  • step (2) in 5 for the purification of cut gum.
  • the recovered product purified by restriction digestion is connected with the pET-28a(+) vector through the action of T4 ligase to construct the recombinant expression plasmid pET28a-PmKuPI.
  • the ligation system is: 6 ⁇ L of the recovered digested and purified product, 2 ⁇ L of pET-28a(+), 1 ⁇ L of 10 ⁇ T4buffer, 1 ⁇ L of T4 ligase, the total system is 10 ⁇ L. Mix lightly, overnight at 16°C.
  • Plasmid extraction Refer to step (3) in 9.2 to obtain the pET28a-PmKuPI recombinant plasmid and store it at -20°C for later use.
  • 3Supernatant and debris of cell lysate Centrifuge the remaining 200 ⁇ L of cell lysate at 15,000 rpm for 10 minutes, collect the supernatant and cell debris of the cell lysate, and mix 90 ⁇ L of 5 ⁇ loading buffer with 180 ⁇ L of supernatant, respectively As a sample. Supernatant of cell lysate. Resuspend all pellets with 150 ⁇ L of 5 ⁇ loading buffer as a sample of cell lysate fragments. The sample was heated at 100°C for 10 min, and centrifuged at 15,000 rpm for 5 min before loading the sample.
  • Binding buffer with 5 times the column bed volume to clean the column with a flow rate of 5 m L/min.
  • sample preparation sample loading.
  • the primary antibody is a rabbit anti-his tag, the antibody company: Sangon Biotech, code: D110002, 1:500 dilution, 37°C, slowly shake for 60 minutes.
  • the secondary antibody is goat anti-rabbit, antibody company: Sangon Biotech, number: D110058, diluted 1:8000, and shaken slowly at 37°C for 60 minutes.
  • the purified target protein was renatured by dialysis, and finally replaced into a soluble buffer (PBS, 10% glycerol, 1ML-arginine, pH 7.4), and compared with the purified protein by SDS-PAGE and Western blot. The purity before sex (precipitation) and after refolding (dissolution).
  • PBS 10% glycerol, 1ML-arginine, pH 7.4
  • the purified protein has antibacterial activity against Escherichia coli, Micrococcus luteus, Aeromonas hydrophila, Pseudomonas aeruginosa, Vibrio parahaemolyticus, Vibrio harveyi, Bacillus subtilis and Staphylococcus aureus.
  • each type of bacteria was cultured in 2216E liquid medium to the logarithmic growth phase. The bacteria were then centrifuged (3,000 ⁇ g, 10 min), washed 3 times with phosphate buffered saline (1 ⁇ PBS), and then resuspended in PBS.
  • PBS was used instead as a control.
  • the purified protein and bacteria mixture was centrifuged at 3000 rpm for 10 min at room temperature for precipitation, and then washed with PBS three times to remove impurities, and then the bacterial pellet was fixed in 200 ⁇ L 3% glutaraldehyde overnight.
  • 200 ⁇ L of 2% sodium phosphotungstate aqueous solution was added to the bacterial suspension, and then dropped on the copper mesh.
  • Use filter paper to remove residual water, and after 5 minutes, air dry the sample. Observe under standard operating conditions with a JEM-1400 (Japan Electronics Corporation) microscope.
  • the PmKuPI gene (SEQ ID No. 1) was cloned by RACE technology and has a full length of 1318 bp, which contains 25 bp of 5′ UTR, 96 bp of 3′ UTR, and 1197 bp of ORF box, encoding a total of 398 amino acids (SEQ ID No. 2) .
  • the molecular weight of PmKuPI is 43.82KDa, and the theoretical isoelectric point is 5.32. To predict its hydrophilicity, it is found that the highest continuous hydrophobicity appears at the 26th position with an index of 2.856, and the highest hydrophilicity appears at the 99th position with an index of -2.978, the total average hydrophilicity coefficient is -0.441, which is a hydrophilic protein.
  • the total number of negatively charged residues (Asp+Glu) is 51, and the total number of positively charged residues (Arg+Lys) is 44. Therefore, PmKuPI is negatively charged as a whole.
  • TMHMM server 2.0 predicts that a transmembrane domain is formed at positions 7-29 ( Figure 2).
  • the existing full-length cDNA sequence of the PmKuPI gene predict the open reading frame ORF and analyze it to obtain the ORF sequence that needs to be recombined. Design and add histidine gene sequence to the recombination ORF sequence, then perform gene synthesis, and then design prokaryotic expression primers . After PCR amplification, the PmKuPI gene fragment is about 1139bp; then the PmKuPI gene and pMD19-T vector are ligated, transformed, and a single colony is selected.
  • the colony of the positive clone is identified by colony PCR, and the plasmid is carried out using the biogenic plasmid extraction kit After extraction of MluI, digested with MluI endonuclease, ligated PmKuPI with pET-28a(+) vector, transformed and identified positive clone colonies by colony PCR.
  • the PmKuPI gene fragment after MluI digestion was about 1750bp.
  • the recombinant expression vector pET28-PmKuPI was transformed into Escherichia coli, similar to the culture method of pET28-PmTLS strain. It can be seen from Figure 8 that the target bands were not seen in lanes NC (whole bacteria), NC1 (supernatant) and NC2 (precipitation) of the negative control group; at the same time, no target bands were seen in the supernatant lanes 3 and 4 at 15°C and 37°C.
  • pET28-PmKuPI-expressing bacteria were cultured with an expression amount of 1L, and induced at 0.5mM IPTG at 15°C for 16h.
  • the results showed that a clear and single band appeared at about 42KDa, indicating that rPmKuPI with higher purity was successfully obtained (Figure 10).
  • the concentration of rPmKuPI was determined by the Bradford protein assay method, and the concentration was 1.00 mg/mL, and a total of 11.27 mg of rPmKuPI was obtained.

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Abstract

提供了一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因、其编码的蛋白质及其在制备抑制微生物的药物中的应用，该马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因的核苷酸序列如SEQ ID No.1所示，其编码的蛋白的氨基酸序列如SEQ ID No.2所示。该马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因编码的蛋白对大肠杆菌、铜绿假单胞菌、嗜水气单胞菌、副溶血弧菌和哈维氏弧菌具有抑制作用。

Description

一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因、编码的蛋白质和应用 技术领域
本发明属于基因工程技术领域，尤其涉及一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因、编码的蛋白质和应用。
背景技术
近年来由于高密度养殖、养殖水域富营养化、生态环境恶化等原因使得贝类养殖品种频发各种由细菌或病毒等引起的感染性疾病。而防治过程大量地使用抗生素等传统药物，破坏了水环境的微生态平衡，使某些病原体对药物产生了耐药性，无法有效地控制疾病的发生，导致马氏珠母贝因病害发生大量死亡，对我国珍珠产业造成了巨大的经济损失。因此，了解马氏珠母贝免疫机制并在此基础上提高马氏珠母贝抗胁迫能力是目前亟需解决的问题。抗菌肽是贝类生物免疫机制中最重要的一个环节，也是贝类在对抗病原体入侵的最重要防线，了解珠母贝体内各种抗菌肽分子的组成及特点对于开发珠母贝抗菌肽来源的新型生物抗生素具有重要意义，但目前对马氏珠母贝抗菌肽的报道甚少，数据库中尚无马氏珠母贝的抗菌肽序列报道。
海洋是世界上物种最为丰富的聚集地，从海洋无脊椎动物中探索出具有抗菌活性的物质，具有极大的潜力。为了解决抗生素滥用和耐药性问题，从水产养殖动物自身出发，探究接近天然的生物抗生素，提高抗菌广谱性和耐药性。
发明内容
有鉴于此，本发明的目的在于提供一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因、编码的蛋白质和应用，本发明提供的基因编码的蛋白对大肠杆菌、铜绿假单胞菌、嗜水气单胞菌、副溶血弧菌和哈维氏弧菌具有抑制作用。
为了实现上述发明目的，本发明提供了以下技术方案：
本发明提供了一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因，所述马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因的核苷酸序列如SEQ IDNo.1所示。
本发明还提供了上述技术方案所述的马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因编码的蛋白，所述蛋白的氨基酸序列如SEQ ID No.2所示。
本发明还提供了上述技术方案所述的蛋白在制备抑制微生物的药物中的应 用。
优选的，所述微生物包括革兰氏阴性菌。
优选的，所述革兰氏阴性菌包括大肠杆菌、铜绿假单胞菌、嗜水气单胞菌、副溶血弧菌和哈维氏弧菌。
本发明的有益效果：
本发明提供了一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因，所述马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因的核苷酸序列如SEQ ID No.1所示，编码的蛋白的氨基酸序列如SEQ ID No.2所示。本发明提供的基因编码的蛋白对大肠杆菌、铜绿假单胞菌、嗜水气单胞菌、副溶血弧菌和哈维氏弧菌具有抑制作用。
附图说明
图1为pMD19-T Vector克隆位点示意图；
图2为马氏珠母贝PmKuPI的跨膜结构域预测；
图3为PmKuPI结构域预测；
图4为PmKuPI同源性比对；
图5为系统进化树构建(Neighbor-joining法)；
图6为PmKuPI基因在马氏珠母贝各组织的表达分布，M：外套膜，B：血细胞，Gi：鳃，Go：性腺，A：闭壳肌，He：肝胰；
图7为PmKuPI原核表达重组质粒验证；
图8为rPmKuPI的诱导表达(SDS-PAGE)，PC1：BSA(1μg)；PC2：BSA(2μg)；M1：Marker；NC：无诱导全菌；1：15℃诱导全菌；2：37℃诱导全菌；NC1：无诱导上清；3：15℃诱导上清；4：37℃诱导上清；NC2：无诱导沉淀；5：15℃诱导沉淀；6：37℃诱导沉淀；
图9为rPmKuPI的诱导表达注(Western Blot)，M2：Marker；NC：无诱导全菌；1：15℃诱导全菌；2：37℃诱导全菌；NC1：无诱导上清；3：15℃诱导上清；4：37℃诱导上清；NC2：无诱导沉淀；5：15℃诱导沉淀；6：37℃诱导沉淀；
图10为rPmKuPI纯化分析注，A：1：BSA(2μg)；M1：Marker；2：复性后的目的蛋白(2μg)；B：M2：Marker；3：复性后的目的蛋白；
图11为rPmKuPI的抗菌活性测定(大肠杆菌)；
图12为rPmKuPI的抗菌活性测定(铜绿假单胞菌)；
图13为rPmKuPI的抗菌活性测定(嗜水气单胞菌)；
图14为rPmKuPI的抗菌活性测定(副溶血弧菌)；
图15为rPmKuPI的抗菌活性测定(哈维氏弧菌)；
图16为rPmKuPI作用于细菌的形态学变化：A和E分别为铜绿假单胞菌和副溶血弧菌的PBS对照组，B、C、D为rPmKuPI作用铜绿假单胞菌的实验组，F、G、H为rPmKuPI作用副溶血弧菌的实验组。
具体实施方式
本发明提供了一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因，所述马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因的核苷酸序列如SEQ ID No.1所示，具体如下：
AAGCAGTGGTATCAACGCAGAGTAC ATGGGGGTGTCAATACTCTATTT AGATATTTACGTTATGATGAGCGTGGTTTGTTACTTTACGTTTATTTTAGGTG CCTTTTTGTTCCTGTGTGATCATGGTATTGCACAGTCACCTTTATCAATATTA CCAGTCCCACCCCCTTTCCCAGACAGGGGCCCTTGCTCAGATAGACCGGCT GTAGTAGGGCCATGCAGAGCACGTCTACGCCGTTATACATACAGAAATGGA AGATGCGAAGAATTTTACTATGGAGGTTGTCTTGGTAACAGAAATAATTTCA GAAGTAGGAGAGAGTGTCAAAGGCAATGTGGCGGGGGAGGTGGAGGCGG AGGAGATATTTGCCAGTTGCCTCATGCACAGCCAGGACCGTGTTTAGCGTA CATGCCACGTTATACATTCAACTCTAACACAGGCCGGTGTGAGGAGTTTATT TACGGTGGTTGTCAAGGAAATGCAAACAGATTCGAGACCCTGCAGGAGTG TAGGAGGCGCTGTGGAGGAGGGGGGCCACCAAGGGACCGTTGCTTTGAA AGACCAAAAGTCCAAGGACCATGTGAAGCTGCTATACCTAGCTTTTCATAC AACCCGAGAACGAGGAGGTGTGAGGAGTTTACATACGGCGGATGTGGAGG AACCCGAAACAGGTTCTCTACGCTCAGAGAATGCCGGGATCGGTGTCAAA GAGGGGGAGGTGGAGGGGGAGGTGTGGACATTTGCGAACTCCCACCCAG GGCCAGTGGACTGTGTTTGGCCTATATCCCTAGCTATTCATACGACTCGGCA AGAGGAGAATGTGTAAGGTTCATTTACGGTGGATGCGGTGGAAATGAAAA CAGATTTGGTTCCCTACAGGAGTGTCAGCGACGATGTGGTGGGGGAGGTG GTGGTGGGGGCGGAGACGGAGATGTGAACGATTTATCTATGGTGGATGTCT GGGAACAAACAATAGGTTTCCTTCTCGAAGAGAATGTGAAAGAAGATGTG GAGACGGCGGTCGACCAAGAAGATGCTTACTGCCCAGAGAGACTGGTCCA TGTAGAGCTGCCTTTCCAAGATACTACTTTAATAGAGAATCTGGACGTTGTG AGAGATTCATATACGGAGGTTGTCAAGGAAACCAAAATAACTTTAGATCAG CAAATGAGTGTAGACGTGTGTGTAGAAGGCGACGAGGGTAAAAATGTCTT CGTCTAAAATTGTAAATATGTACTTTAAGATTTTAGTTGCAATTAAGGTGAATTAAAGCACTAATTAATTCGTCAAAAAAAAAAAAAAAAAAAAAAAAAAAAA。下划线为马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因的开放阅读框。
本发明还提供了上述技术方案所述的马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因编码的蛋白，所述蛋白的氨基酸序列如SEQ ID No.2所示，具体如下：
Figure PCTCN2020137155-appb-000001
本发明还提供了上述技术方案所述的蛋白在制备抑制微生物的药物中的应用。在本发明中，所述微生物优选包括革兰氏阴性菌，所述革兰氏阴性菌优选包括大肠杆菌、铜绿假单胞菌、嗜水气单胞菌、副溶血弧菌和哈维氏弧菌。
下面结合实施例对本发明提供的技术方案进行详细的说明，但是不能把它们理解为对本发明保护范围的限定。
实施例1
1、马氏珠母贝免疫效应分子筛选
从在线抗菌肽数据库(APD3，http://aps.unmc.edu/AP/main.php)，PubMed(https://www.ncbi.nlm.nih.gov/pubmed/)和国家生物技术信息中心(NCBI)数据库(https://www.ncbi.nlm.nih.gov/)获取所有具有先前验证的抗微生物活性的氨基酸序列，随后，构建了一个本地参考AMP数据库，根据马氏珠母贝基因组数据进行比对搜索。收集比对率最高的基因序列，再运用NCBI数据库中的在线Blast进行分析，预测所收集的免疫效应分子PmKuPI基因的类型。
2、PmKuPI基因相关引物设计
PmKuPI基因的特异性引物使用Primer Premier 5.0设计。5'端和3'端特异性 引物依据RACE扩增原理设计，经过比对拼接获得基因的cDNA全长。引物序列如下。
表1引物
引物 序号 序列(5'-3') 用途
PmKuPI-3'-inner SEQ ID No.3 CTATTCATACGACTCGGCAAGA 3'-RACE
PmKuPI-3'-outer SEQ ID No.4 CCCGAAACAGGTTCTCTACGCT 3'-RACE
PmKuPI-5'-inner SEQ ID No.5 TGTTTTCATTTCCACCGCATCC 5'-RACE
PmKuPI-5'-outer SEQ ID No.6 CAGTCTCTCTGGGCAGTAAGCATC 5'-RACE
M13-F SEQ ID No.7 CGCCAGGGTTTTCCCAGTCACGAC 菌落PCR检测
M13-R SEQ ID No.8 GAGCGGATAACAATTTCACACAGG 菌落PCR检测
PmKuPI-RT-F SEQ ID No.9 TTCATACAACCCGAGAACGAGG 荧光定量
PmKuPI-RT-R SEQ ID No.10 GTTTTCATTTCCACCGCATCC 荧光定量
GAPDH-F SEQ ID No.11 GCAGATGGTGCCGAGTATGT 内参基因
GAPDH-R SEQ ID No.12 CGTTGATTATCTTGGCGAGTG 内参基因
3、总RNA提取
(1)获取马氏珠母贝全组织样品，加Trizol并研磨各组织，依照Trizol法原理提取总RNA。
(2)1％琼脂糖凝胶电泳检测RNA完整性和质量。
(3)微量核酸定量仪测定总RNA的浓度与纯度。
(4)所获总RNA于-80℃超低温冰箱保存备用。
4、cDNA第一链的合成
依照Reverse Transcriptase M-MLV试剂盒操作制备所需模板。具体程序如下：
(1)RNA与引物结合，PCR程序为70℃，10min，冰上放置2～3min。加样体系如下：
表2加样体系
试剂 剂量
总RNA 1ng～1μg
Oligo(dT)(50uM) 1μL
RNase-free water 补加至8μL
(2)向上述RNA体系中加入以下试剂：
表3试剂
试剂 剂量
5×M-MLV Buffer 2.0μL
dNTP Mixture(10m M) 0.5μL
RNase Inhibitor 0.25μL
RTase M-MLV(RNase H-) 0.25～1μL
RNase-free water 补至12μL
(3)离心混匀数秒，进行PCR，程序为：42℃，60min；70℃，15min。
5、中间片段克隆
(1)PrimeSTARHS高保真酶扩增获得目的片段。PCR反应体系如下：
表4反应体系
试剂 体积
PrimeSTARHS 5μL
模板 0.4μL
上游引物 0.4μL
下游引物 0.4μL
ddH 2O 3.8μL
Total 10μL
采用3步法扩增。PCR反应程序如下：
Figure PCTCN2020137155-appb-000002
(2)凝胶检测及目的片段回收
吸1μL PCR产物用1％琼脂糖电泳检测，扩大目的片段体系，参照PCR产物回收试剂盒(Gene JET Gel Extraction Kit)说明书回收PCR产物。
(3)目的片段连接
将纯化后的PCR产物连接到pMD-19T Vector载体上(图1)。体系如下：
表5体系
试剂 剂量
Solution I 5μL
目的片段 4.5μL
pMD19-T Vector 0.5μL
Total 10μL
连接程序为：16℃连接约16h。
(4)转化
将DH5α感受态细胞从超低温冰箱取出，放冰上至微溶，再将连接产物加入含100μL DH5α感受态细胞的管子中，轻轻吹打均匀；冰上放置30min，42℃热激60～90s，冰上放置2～3min；接着加入890μL提前37℃预热好的LB液体培养基，37℃200rpm振荡培养1h；然后4000rpm 2min，弃上清，留下约100μL，轻轻吹散悬浮细胞，并涂于LA(Amp+)固体平板上；最后，37℃先正置培养半小时后，再倒置培养过夜。
(5)菌落PCR检测
挑取单菌落接种于LA(含Amp+)液体培养基中，37℃，220rpm振荡培养6h左右。M13通用引物鉴定阳性克隆，经1％琼脂糖凝胶电泳检测的阳性菌落送到广州生工测序。具体体系与程序如下：
表6体系
Premix Taq 5.0μL
引物M13-F(10μM) 0.4μL
引物M13-R(10μM) 0.4μL
菌液DNA 0.4μL
ddH 2O 3.8μL
Total 10μL
表7程序
Figure PCTCN2020137155-appb-000003
6、3′和5′端RACE扩增
参照SMARTTM RACE cDNA Amptification kit说明书制备3′和5′RACE的cDNA模板。巢式PCR以3′、5′特异性引物结合通用引物(NUP和UPM)扩增。
(1)第一轮RACE反应
表8体系
试剂 体积
PrimeSTAR HS 5μL
3′/5′cDNA模板 0.4μL
UPM引物 0.4μL
Outer特异性引物 0.4μL
ddH 2O 3.8μL
Total 10μL
PCR反应程序：
Figure PCTCN2020137155-appb-000004
(2)第二轮RACE反应
表9体系
试剂 体积
Premix Taq 5μL
3′/5′cDNA模板 0.4μL
NUP引物 0.4μL
Inner特异性引物 0.4μL
ddH 2O 3.8μL
Total 10μL
PCR反应程序：
Figure PCTCN2020137155-appb-000005
(3)PCR切胶回收/产物纯化，连接、转化以及菌落PCR检测参考5(2)～(5)。
7、生物信息学分析
利用NCBI blastx进行序列同源性和相似性分析；DNAMAN 6.0软件序列查找、拼接和比对；ExPASy在线预测其理论分子量(MW)和等电点(pI)；采用SignalP 4.0 Server进行信号肽序列预测；TMHMM Server v.2.0分析序列的跨膜结构域；MEGA 6软件以NJ法构建系统进化树；SoftBerry Psite对其推导的氨基酸序列功能位点的预测；SOPMA预测蛋白质二级结构。
8、组织表达及PAMPs刺激后时序表达分析
8.1贝的处理及样品采集
(1)组织定量：取10只规格一致、活力较好的贝，采集组织为性腺、鳃、外套膜、血淋巴、闭壳肌和肝胰腺。
(2)PAMPs刺激：取暂养1周健康的马氏珠母贝320只，随机分成4组：LPS刺激组(实验组)、PGN刺激组(实验组)、PolyI:C刺激组(实验组)、PBS组(对照组)，各80只贝。采用闭壳肌注射的方法，实验组每只注射100μL的LPS、PGN、PolyI:C(10μg/mL)，注射100μL PBS作为对照组。注射后的0、3、6、12、24、48、72、96h，各组分别随机抽取10只贝取全组织备用，其中血淋巴于4℃，800×g，离心15min后，舍弃上清，加1mL Trizol，轻轻摇荡使悬浮均匀，提取总RNA反转录成cDNA，用于后面的定量分析(注：PBS进行了灭菌处理，LPS、PGN、PolyI:C由灭菌的PBS配制；实验过程中，不喂饵料，且 未出现死亡现象)。
8.2引物设计
荧光定量PCR反应中所用引物见表1。
8.3总RNA的提取
总RNA的提取方法同3中的步骤(1)～(4)。
8.4荧光定量cDNA模板的制备
依照Reverse Transcriptase M-MLV(RNase H)说明书操作。
(1)RNA与引物结合，PCR程序为70℃，10min，冰上放置2～3min。加样体系如下：
表10加样体系
试剂 体积
总RNA 1ng～1μg
Random Primers(25uM) 1μL
RNase-free water 补加至8μL
(2)向上述RNA体系中加入以下试剂：
表11试剂
试剂 剂量
5×M-MLV Buffer 2.0μL
dNTP Mixture(10m M) 0.5μL
RNase Inhibitor 0.25μL
RTase M-MLV(RNase H-) 0.25～1μL
RNase-free water 补至12μL
(3)离心混匀数秒，进行PC，程序为：42℃，60min；70℃，15min，所得的cDNA第一链于-20℃保存。
8.5荧光定量PCR
以8.4的反转录cDNA为模板，内参基因选择GAPDH。按3个实验重复设置加样孔。按照以下反应体系和反应条件实时荧光定量PCR：
表12体系
Figure PCTCN2020137155-appb-000006
Figure PCTCN2020137155-appb-000007
反应程序：
Figure PCTCN2020137155-appb-000008
8.6数据统计与分析
荧光定量的数据采用2-△△ct法进行分析。试验结果均采用平均值±标准差表示，用SPSS17.0软件进行单因素方差分析(one-way ANOVA)，并用Duncan’s多重比较对均值进行差异显著性检验。
9、重组蛋白制备
9.1基因合成
根据已有的目的基因序列进行基因合成，以此作为后续亚克隆的模板，引入酶切位点为NcoI和HindIII。
9.2原核表达载体构建
(1)重组PmKuPI ORF扩增，PCR体系为：10μL的Premix Ex Taq，0.5μL合成模板，Forward Primer和Reverse Primer各0.4μL，ddH 2O补足体系至20μL。程序为：94℃变性5min；98℃10s，55℃30s，72℃60s，30个循环。凝胶电泳检测反应产物。
(2)PmKuPI的克隆与测序见步骤5。
(3)质粒抽提参照Easy Pure Plasmid Mini Prep Kit硅胶膜离心柱质粒DNA小量抽提试剂盒说明书提取。
(4)用MluⅠ、XhoI和HindIII内切酶对空质粒pET-28a(+)和抽提的重组质粒进行双酶切。体系为5.0μL的10×FD Buffer，MluⅠ内切酶3.0μL，20μL的质粒，ddH 2O补足体系至50μL。轻微混匀，37℃保温2h。
(5)切胶纯化参照5中的步骤(2)。
(6)酶切纯化的回收产物通过T4连接酶的作用与pET-28a(+)载体连接构建重组表达质粒pET28a-PmKuPI。连接体系为：回收的酶切纯化产物6μL，2μL的pET-28a(+)，10×T4buffer为1μL，1μL T4连接酶，总体系为10μL。轻微混匀，16℃过夜。
(7)连接产物的转化入、阳性克隆筛选及测序参照5中的步骤(4)～(5)。
(8)质粒提取参照9.2中的步骤(3)，即获得pET28a-PmKuPI重组质粒，-20℃保存备用。
9.3重组融合蛋白的诱导表达
(1)转化、筛选阳性克隆
从超低温冰箱取出感受态细胞BL21(DE3)，先冰解；将100ng质粒DNA加入BL21(DE3)菌株并轻轻混合，试管在冰上孵育30min，震动管在42℃加热90s，不要摇晃，将试管放在冰上放置3min，加入100μL室温LB培养基。摇动并在37℃下于200rpm孵育管60min，在含50μg/mL卡那霉素的LB琼脂平板上铺展，将板倒置在37℃下孵育过夜。筛选阳性克隆并测序。
(2)小试培养选择最佳的诱导条件
挑选三个分离良好的单个菌落，分别接种到含有50μg/mL卡那霉素的4mL LB培养基中，将细胞在37℃的摇床上以200rpm摇动孵育，当OD600值达到0.6～0.8时，在三根管中的两根加入IPTG，最后浓度为0.5mM的IPTG分别在15℃诱导16h和37℃诱导4h，第三根试管作为阴性对照；
(3)重组蛋白制备与检测
①从450μL培养物中收获细胞沉淀，用超声仪裂解1min。
②全细胞裂解液：将50μL 5×上样缓冲液与100μL细胞裂解液混合，作为全细胞裂解液的样品，在100℃下加热样品10min，然后以15,000rpm离心5min。
③细胞裂解液的上清液和碎片：将剩余的200μL细胞裂解液以15,000rpm离心10min，收集细胞裂解液的上清液和细胞碎片，分别将90μL5×上样缓冲液与180μL上清液混合作为样品。细胞裂解液的上清液。用150μL 5×上样缓冲液 重悬所有沉淀，作为细胞裂解液碎片的样品。将样品在100℃下加热10min，并在上样之前以15,000rpm离心5min。
④使用SDS-PAGE和Western blot检测蛋白的表达和溶解度，最后大量诱导表达融合蛋白。
9.4融合蛋白的分离纯化
(1)超声破碎菌体
①将收集的细菌菌体用Buffer(50mM Tris，150mM NaCl，5％甘油pH 8.0)溶解，冰浴中超声破碎菌体，功率350W，30min(超声4s，暂停6s为一个循环)。
②超声完毕，12,000rpm，4℃，离心20min，弃上清，沉淀用破碎Buffer溶解，冰浴中超声破碎，功率350W，30min(超声4s，暂停6s为一个循环)。
③超声完毕，12,000rpm，4℃，离心20min，收集上清进行下一步纯化。
(2)镍琼脂糖亲和层析
①取5mL Ni-NTA，用5倍柱床体积的Binding buffer清洗平衡柱子，流速5mL/min。
②填料和样品孵育1h后上柱，收集穿透液。
③5倍柱床体积的Binding buffer清洗柱子，流速5m L/min。
④Wash buffer洗杂，流速5mL/min，收集洗脱液。
⑤Elution buffer洗脱，流速2mL/min，收集洗脱液。
⑥收集样品SDS-PAGE检测
(3)纯化蛋白SDS-PAGE检测
准备12％的SDS-PAGE，Tris-Gly电泳缓冲液，浓缩胶80V，20min，分离胶120V，60min，凝胶电泳结束后进行考马斯亮蓝染色20min，脱色过夜。
(4)Western blot检测
①制胶：制备聚丙烯酰胺凝胶：浓缩胶5％，分离胶12％
②制样：上样。
③电泳：浓缩胶80V，30min；分离胶120V，60min。
④转膜：湿转，250mA，90min。
⑤封闭：5％的脱脂奶粉，37℃缓慢振荡2h。
⑥孵育一抗：一抗为兔抗his标签，抗体公司：Sangon Biotech，编号：D110002， 1:500稀释，37℃缓慢振荡60min。
⑦孵育二抗：二抗为羊抗兔，抗体公司：Sangon Biotech，编号：D110058，1:8000稀释，37℃缓慢振荡60min。
⑧显色：TMB显色。
(5)包涵体蛋白复性
将纯化后的目的蛋白进行透析复性，并最终置换至可溶性的缓冲液中(PBS，10％甘油，1ML-精氨酸,pH 7.4)，并运用SDS-PAGE和Western blot检测对比纯化蛋白复性前(沉淀)和复性后(溶解)的纯度。
10、纯化蛋白抗菌活性检测
纯化的蛋白对大肠杆菌，藤黄微球菌，嗜水气单胞菌，铜绿假单胞菌，副溶血弧菌，哈维氏弧菌，枯草芽孢杆菌和金黄色葡萄球菌的抗菌活性。首先，将每种细菌分别在2216E液体培养基中培养至对数生长期。然后将细菌离心(3,000×g，10min)，用磷酸盐缓冲盐水(1×PBS)洗涤3次，然后重悬于PBS中。接下来，用96孔酶标板将50μL的纯化蛋白(200μg/mL)与10μL的每种细菌悬液分别混合，并在室温下孵育2h。PBS用作阴性对照。然后在每个混合孔中加入140μL培养基，在37℃恒温培养箱孵育培养，同时使用酶标仪(EnSpire，PerkinElmer)测定在添加纯化蛋白和PBS后的0、1、2、3、4、5、6、7、8、9、10、11和12h测量OD600值。每个样品平行进行三个实验。
11、透射电镜观察纯化蛋白作用细菌后的形态变化
在37℃下用200μL的纯化蛋白处理200μL的处于指数生长期的细菌2h。PBS代替作为对照。之后在室温下先将纯化蛋白与细菌混合物以3000rpm离心10min进行沉淀，再用PBS洗涤3次去除杂质，然后将细菌沉淀用200μL 3％戊二醛中固定过夜。处理后，将200μL 2％磷钨酸钠水溶液添加到细菌悬浮液中，然后将其滴在铜网上。使用滤纸除去残留的水，5min后，将样品风干。在标准操作条件下用JEM-1400(日本电子公司)显微镜进行观察。
12、结果与分析
12.1 PmKuPI的基因克隆
通过RACE技术克隆得到PmKuPI基因(SEQ ID No.1)全长为1318bp，其中包含25bp的5′UTR，96bp的3′UTR，1197bp的ORF框，共编码398个氨基酸(SEQ ID No.2)。
12.2 PmKuPI理化性质分析
PmKuPI的分子量为43.82KDa，理论等电点为5.32，预测其亲水性，发现在第26位出现连续的最高疏水性，其指数为2.856，在第99位出现最高亲水性，其指数为-2.978，总的平均亲水性系数为-0.441，为亲水性蛋白。带负电荷的残基总数(Asp+Glu)为51，带正电荷的残基总数(Arg+Lys)为44，因此，PmKuPI总体带负电荷。TMHMM server 2.0预测发现，在第7-29位形成一个跨膜结构域(图2)。SOPMA软件预测二级结构显示，无规则卷曲占整体的49.50％，α-螺旋结构27.39％，延伸链19.85％，β-转角3.27％。SMART分析结果表明，PmKuPI氨基酸序列形成了四个串联的Kunitz域，分别在第53-105位，第113-167位，第174-228位和第238-292位(图3)。
12.3 PmKuPI同源性分析
通过DNAMAN将PmKuPI氨基酸序列与其它无脊椎动物的相应氨基酸进行多序列比对，分析发现PmKuPI与长牡蛎相似性最高，为30.14％，而与其他物种相似性都较低，物种间一致相似性为23.43％(图4)。
使用MEGA 6构建系统进化树，在PmKuPI的进化树分类中发现软体类单独聚为一小支，其中马氏珠母贝与长牡蛎和美洲牡蛎(Crassostrea virginica)的亲缘关系都很近(图5)。
12.4 PmKuPI基因mRNA的组织定量分析
利用Real-time PCR检测PmKuPI蛋白酶抑制剂基因mRNA在马氏珠母贝血细胞等6个组织中的表达模式情况。结果发现：PmKuPI蛋白酶抑制剂基因在外套膜中的表达水平最高(p<0.01)，而在其它组织中，几乎无表达(图6)。
12.5 PmKuPI重组蛋白的表达
(1)PmKuPI原核表达载体的构建
根据已有的PmKuPI基因全长cDNA序列，预测开放阅读框ORF并进行分析，获得需要重组的ORF序列，在重组ORF序列中设计添加组氨酸基因序列，然后进行基因合成，再设计原核表达引物。PCR扩增后得到PmKuPI基因片段约1139bp；随后将PmKuPI基因与pMD19-T载体进行连接、转化并挑取单菌落，通过菌落PCR鉴定出阳性克隆的菌落，利用生工质粒抽提试剂盒进行质粒的抽提，然后MluI内切酶消化，并将PmKuPI与pET-28a(+)载体相连接、转化并通过菌落PCR鉴定阳性克隆菌落，MluI消化后的PmKuPI基因片段约为1750bp。 随后对有阳性克隆结果的进行质粒抽提，抽提获得的质粒即为pET28-PmKuPI的重组质粒，重组蛋白预计分子量分别为41.32KDa。菌落PCR鉴定、MluI消化鉴定(图7)及测序的结果都验证表明pET28-PmKuPI载体构建成功。
(2)PmKuPI重组蛋白(rPmKuPI)的诱导表达
将重组表达载体pET28-PmKuPI转化至大肠杆菌，类似于pET28-PmTLS菌株的培养方法。从图8可知，阴性对照组泳道NC(全菌)、NC1(上清)和NC2(沉淀)未出现目的条带；同时15℃和37℃的上清泳道3和4中也未见目的条带；在15℃的泳道1(全菌)和5(沉淀)中出现目的条带，而37℃的泳道2(全菌)和6(沉淀)中也出现的目的条带，但两者中出现的目的条带都不太明显(图8)。用Western blot进一步验证，结果显示，在15℃和37℃诱导的泳道1、2(全菌)和5、6(沉淀)中约42KDa处出现清晰单一染色条带，与理论值41.52KDa一致，表明成功获得了的重组蛋白(图9)。最终rPmKuPI诱导的最佳温度选择了15℃，并且主要以包涵体形式表达。
为了获得大量融合蛋白，以1L的表达量培养pET28-PmKuPI的表达菌，在0.5mM IPTG，15℃下诱导16h。结果显示，在约42KDa处出现一条清晰单一的条带，表明成功获得了纯度较高的rPmKuPI(图10)。通过Bradford蛋白测定法测定rPmKuPI浓度，其浓度为1.00mg/mL，共获得rPmKuPI 11.27mg。
12.6 rPmKuPI的抗菌活性测定
在细菌液体生长曲线抑制实验中，总共测定了8种细菌，其中3种为革兰氏阳性菌，5种为革兰氏阴性菌，rPmKuPI显著抑制了5种革兰氏阴性菌种的生长(P<0.05)，分别是大肠杆菌、铜绿假单胞菌、嗜水气单胞菌、副溶血弧菌和哈维氏弧菌(图11-15)，但对革兰氏阳性菌的生长几乎没有影响。
12.7 rPmKuPI抗菌作用机制
为了了解马氏珠母贝的TLS的抗菌作用机制，将rPmKuPI溶液分别与铜绿假单胞菌和副溶血弧菌一起反应2h，滴网，在透射电子显微镜下镜检。结果如图16所示，从图中可以看出，铜绿假单胞菌的对照组(图16中的A)边缘清晰完整，菌体细长，内含物质致密状且均匀；而实验组(图16中的B)可观察到铜绿假单胞菌的菌体略微膨胀，内含物质缺失，内部结构和对照组相比也发生明显改变，菌体一端也有内含物质释放出来。同时，将实验组两端放大再观察，发现靠近细胞壁两边的内含物质大部分缺失，菌体趋向于空壳状态(图16中的C, D)。图16中的E为副溶血弧菌的对照组，菌体为短杆状，均质饱满；而实验组(图16中的F)内含物收缩，出现折叠现象；进一步放大再观察，发现内含物质与细胞壁基本脱离，并且有明显的折皱和缺失(图16中的G，H)。
以上所述仅是本发明的优选实施方式，应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以做出若干改进和润饰，这些改进和润饰也应视为本发明的保护范围。

Claims (5)

  1. 一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因，所述马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因的核苷酸序列如SEQ ID No.1所示。
  2. 权利要求1所述的马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因编码的蛋白，其特征在于，所述蛋白的氨基酸序列如SEQ ID No.2所示。
  3. 权利要求2所述的蛋白在制备抑制微生物的药物中的应用。
  4. 根据权利要求3所述的应用，其特征在于，所述微生物包括革兰氏阴性菌。
  5. 根据权利要求4所述的应用，其特征在于，所述革兰氏阴性菌包括大肠杆菌、铜绿假单胞菌、嗜水气单胞菌、副溶血弧菌和哈维氏弧菌。
PCT/CN2020/137155 2020-06-24 2020-12-17 一种马氏珠母贝Kunitz型丝氨酸蛋白酶抑制剂基因、编码的蛋白质和应用 WO2021258679A1 (zh)

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