An inhibitory polypeptide targeting the s1 protein of porcine viral diarrhea virus

Abstract

This invention utilizes a machine learning model to analyze the S1-CTD region of the PEDV S protein crystal structure. Through virtual peptide screening, a peptide sequence of FWKEAK (110616) with potential affinity for the target protein was identified. The 110616 sequence was artificially synthesized in a solid phase, and the peptide was screened using ELISA with artificially expressed PEDV S1 protein. The affinity constant between the peptide and the target protein was determined using surface plasmon resonance (SPR) assays. The cytotoxicity of peptide 110616 was tested using a CCK-8 assay kit. Its inhibitory activity against viral infection was assessed using quantitative real-time PCR and indirect immunofluorescence assays. The results showed that the 110616 sequence significantly inhibited PEDV infection.

Description

Technical Field

[0001] This invention relates to polypeptide sequences that specifically bind to the S1 protein of porcine viral diarrhea virus and their applications, belonging to the fields of polypeptide design, virus inhibition, and drug screening and development. Background Technology

[0002] Porcine epidemic diarrhea virus (PEDV) encodes four major structural proteins: spike (S), nucleocapsid (N), membrane (M), and envelope (E). The S protein, processed by trypsin-like host cell proteases into S1 and S2 subunits, plays a crucial role in the viral attachment to host cells. The S1-CTD region of the PEDV S protein is one of the key targets for the development of antiviral drugs against PEDV. However, existing PEDV vaccines do not provide adequate protection against prevalent PEDV infections. Considering this factor, research targeting novel PEDV strains is essential for the prevention and control of emerging or re-emerging infectious diseases.

[0003] For most coronaviruses, the N-terminal domain (NTD) of the S1 subunit attaches to cellular carbohydrates, while the C-terminal domain binds to cellular protein receptors. The RBD of the SARS-CoV-2 S1 subunit is responsible for the binding of viral receptors to host cell receptors. However, some coronavirus infection studies have reported that synthetic peptides targeting the SARS-CoV-2 RBD domain can prevent viral entry into cells. Therefore, the RBD is an important target for developing viral attachment inhibitors, including neutralizing antibodies (nAbs). The S1-CTD domain in the S1 subunit of the PEDV S protein can stimulate the production of neutralizing antibodies in animals, making it a relatively conserved target for developing antiviral peptides.

[0004] Peptides have relatively simple structures and small molecular weights, making them easy to synthesize and modify. They also exhibit high cell membrane permeability, no cytotoxicity, and low immunogenicity. Common methods for screening peptides include phage display, mRNA display, combinatorial chemistry, and computer-based virtual screening. However, these methods heavily rely on high-throughput experimental screening, which can significantly increase workload. Structure-based molecular docking techniques can overcome this problem. Molecular docking is a key technology in computational virtual screening, attempting to predict the binding mode and affinity of ligands to the active sites of proteins. It offers many advantages, such as simplicity, speed, reduced workload in peptide screening, shorter development cycles, and improved screening success rates. Summary of the Invention

[0005] This invention utilizes a machine learning model to analyze the S1-CTD region of the PEDV S protein crystal structure. Through virtual peptide screening, a peptide sequence of FWKEAK (110616) with potential affinity for the target protein was identified. The 110616 sequence was artificially synthesized in a solid phase, and the peptide was screened using ELISA with artificially expressed PEDV S1 protein. The affinity constant between the peptide and the target protein was determined using surface plasmon resonance (SPR) assays. The cytotoxicity of peptide 110616 was tested using a CCK-8 assay. Its inhibitory activity against viral infection was assessed using quantitative real-time PCR and indirect immunofluorescence assays. The results showed that the 110616 sequence significantly inhibited PEDV infection.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A polypeptide sequence that specifically binds to the S1 protein of porcine viral diarrhea virus, characterized in that the polypeptide sequence is FWKEAK.

[0008] The polypeptide sequence is characterized in that it includes the polypeptide sequence described above as the core, and any modifications or alterations made to the polypeptide sequence based on it; the modifying materials include, but are not limited to, nanomaterials, fluorescent materials, enzymes, biotin, and specific proteins; the modifying materials include, but are not limited to, natural amino acids and non-natural amino acids.

[0009] The aforementioned polypeptide sequence has applications in the detection and inhibition of porcine viral diarrhea virus.

[0010] The beneficial effects of this invention are:

[0011] 1. Based on the S1-CTD region of the PEDV S1 protein crystal structure, this invention utilizes molecular docking virtual screening technology and a machine learning model to obtain a polypeptide sequence 110616 that specifically binds to PEDV S1. The polypeptide sequence is FWKEAK. The equilibrium dissociation constant K between the polypeptide and the PEDV S1 protein is determined by surface plasmon resonance detection. D It is 7.721×10 -7 M, or 772nM, indicates a high affinity.

[0012] 2. The peptide designed in this invention was used in a viral inhibition experiment at the cellular level. The effective concentration of the peptide that inhibited the virus reached 3.125 µM, demonstrating outstanding viral inhibition effect. Attached Figure Description

[0013] Figure 1 The docking results of the 110616 sequence with the PEDV S protein are shown.

[0014] Figure 2 The figure shows the SPR affinity determination results between the 110616 sequence and the PEDV S1 protein. In the figure, the curves from top to bottom represent 25 µM, 12.5 µM, 6.25 µM, 3.125 µM, and 1.5625 µM. The vertical axis represents the signal value detected by the sensor; the horizontal axis represents the time of sample interaction within the sensor.

[0015] Figure 3 shows the ELISA identification results of 110616 and artificially expressed PEDV S1 protein.

[0016] Figure 4 The results show the cytotoxicity of 110616 against Vero cells.

[0017] Figure 5 The results of qRT-PCR identification of 110616 inhibiting PEDV infection in Vero cells.

[0018] Figure 6 The results of indirect immunofluorescence identification of 110616 inhibiting PEDV infection of Vero cells. Detailed Implementation

[0019] The specific embodiments of the present invention will be further described in detail below with reference to examples.

[0020] Example 1: Molecular docking and screening of virtual peptide libraries

[0021] PEDV S structure data (PDB ID: 6U7K) was downloaded from a protein structure library. Water molecules and other irrelevant molecules were removed, and the integrity of the side chains was assessed. Complete side chain groups were added, and the energy of the entire protein structure was minimized. A computer-generated peptide library was used to perform virtual docking with the protein structure, and the mechanical parameters of intermolecular interactions were calculated. Using the determined peptide-protein affinity constants and interaction mechanics as the training set, a random forest machine learning method was used to build a peptide affinity prediction model. The quality of the predictions was used to screen peptides, and peptides with the best evaluation value (E score) were selected as candidate peptides for further peptide synthesis and functional verification. The peptide-protein interaction model prediction results (see...) Figure 1 ).

[0022] Example 2: Affinity determination (SPR) of 110616 with PEDV S1 protein.

[0023] 1. Before immobilizing the protein onto the chip, a suitable buffer pH needs to be selected to allow the ligands to accumulate near the chip surface through electrostatic adsorption, achieving a better coupling effect. The PEDV S1 sample was diluted to 50 μg / mL using sodium acetate solutions at pH 5.5, 5.0, 4.5, and 4.0. The loading time was 180 s, and 50 mM NaOH was used as the washing solution. Based on the results, pH 4.0 was determined to be the optimal coupling condition.

[0024] 2. Immobilize PEDV S1 onto the CM5 chip surface using the direct coupling method. Select channels, with Flow Cell 1 as the reference channel and Flow Cell 2 as the sample channel. Choose amino-coupling (Amine) as the coupling method.

[0025] Select "Specify contact time" as the coupling method: use a fixed contact time as the coupling standard. Click "next," select "load sample," remove the sample tray, and place the required reagents one by one according to the diagram in the table. Place the sample tray back in the tray and click "next." Check the buffer solution, etc., and save the method and result files. Click "run" to start the actual coupling. The final coupling level will be displayed after coupling is complete.

[0026] 3. Select Run Kinetics / Affinity Assay, then click Kinetics / Affinity to set the relevant experimental parameters. Select Flow Cell 1 or 2 and the chip type CM5. The Startup solution is HBS-EP buffer, with a binding time of 120s, a dissociation time of 120s, a regeneration solution of 0.25% SDS, and a stabilization time of 30s. Enter the sample name, molecular weight, and concentration. Dissolve the sample in HBS-EP, dilute to different concentrations, and set up a zero-concentration and a minimum concentration replicate. Place the sample as required, check the buffer, save the file, and click Run to begin the experiment.

[0027] 4. After the experiment, the results were analyzed using Evaluation software. The background signal of Flow Cell2 minus 1 was used as the experimental result. A 1:1 binding fitting method was used for fitting.

[0028] The results showed that 110616 had a good affinity for artificially expressed PEDV S1 protein, and the equilibrium dissociation constant K between the two proteins was [missing information]. D It is 7.721×10 -7 M, i.e., 772nM, (see...) Figure 2 ).

[0029] Example 3: ELISA identification of 110616 and artificially expressed S1 protein

[0030] 1. Artificially expressed and purified PEDV S1 protein was coated onto an ELISA plate at a concentration of 2 μg / ml (protein content). The coating antigen was diluted with carbonate (CBS) buffer. 100 μL of the solution was added to each well of a 96-well ELISA plate and incubated overnight at 4°C. The plate was then washed 5 times with PBST buffer and blocked with 5% skim milk.

[0031] 2. Dilute the artificially synthesized 110616 dry powder modified with a His tag at the amino terminus to a concentration of 1 μg / ml with PBS buffer (pH 7.4), add 100 μL to each well of the above microplate, mix well, and incubate at 37°C in the dark for 30 min.

[0032] 3. Wash 5 times with PBST buffer and shake off the liquid in the wells of the ELISA plate; dilute the mouse His tag antibody with 5% skim milk at a ratio of 1:1000, add 100 μL to each well of the shaken ELISA plate, mix well, and incubate at 37°C in the dark for 45 min.

[0033] 4. Wash 5 times with PBST buffer and shake off the liquid in the wells of the microplate; dilute the HRP-labeled goat anti-mouse secondary antibody 1:1000 with 5% skim milk, add 100 μL to each well of the shaken microplate, mix well, and incubate at 37°C in the dark for 30 min.

[0034] 5. According to the required amount for the experiment, add 100 μL of TMB chromogenic solution to each well of the above microplate, mix thoroughly for 30 seconds, and then develop the color for 10 minutes at room temperature.

[0035] 6. Add 50 μL of 2M sulfuric acid stop solution to each well of the above ELISA plate, mix thoroughly for 30 seconds, and then read the absorbance value of each well at 450 nm on the ELISA instrument to determine the result.

[0036] The results showed that 110616 had good affinity and specificity for artificially expressed PEDV S1 protein (see [link to study]). Figure 3A-B ).

[0037] Example 4: Identification of Vero cytotoxicity of 110616

[0038] 1. Select Vero cells in good growth condition. When the cells form a monolayer or reach 80%-90% confluence, discard the culture medium, wash three times with sterile PBS, and then add 1 ml of 0.25% trypsin to digest the adherent cells. After complete cell digestion, add an appropriate amount of DMEM medium containing 10% FBS, disperse the cells, and adjust the density to 1×10⁶ cells / cm² based on cell count. 5 Cells / ml were added to 96-well cell culture plates, 100 μL per well; the plates were incubated at 37℃ in a 5% CO2 incubator for 24 h. When the cells reached 80%-90% confluence, the culture medium was discarded, and the plates were washed three times with sterile PBS (to avoid edge effects, the outermost wells of the cell culture plate were not used for experiments). Blank, control, and experimental groups were set up. The blank group received only 100 μL of complete culture medium, without cell suspension; the control and experimental groups received 100 μL of cell suspension per well, with at least three parallel wells in each group.

[0039] 2. Dilute the peptide powder to 4 mg / ml with sterile ultrapure water. Based on the molecular weight of peptide 110616 (MW: 1597.85), serially dilute it with serum-free DMEM at the following concentrations: 400 μM, 200 μM, 100 μM, 50 μM, 25 μM, 12.5 μM, 6.25 μM, 3.125 μM, 1.5625 μM, and 0.78125 μM.

[0040] 3. After culturing cells for 24 hours, observe the cells and replace them with new culture medium: replace the blank group and control group with complete culture medium; replace the experimental group with culture medium containing 0.78125μM, 1.5625μM, 3.125μM, 6.25μM, 12.5μM, 25μM, 50μM, 100μM, 200μM, and 400μM.

[0041] 4. After culturing cells for another 24 hours, 100 μL of complete culture medium containing 10 μL of CK-8 solution was added to each well, and the cells were cultured for another hour. Finally, the absorbance of the cell culture plate was measured using a microplate reader at a wavelength of 450 nm. The cytotoxicity of the 110616 peptide was assessed using the formula: Cell viability (100%) = Experimental group OD450 - Blank OD450 / Control group OD450 - Blank OD450.

[0042] The results showed that 110616 was not toxic to Vero cells to some extent (see...). Figure 4 ).

[0043] Example 5: qRT-PCR identification of 110616 inhibiting PEDV infection in Vero cells

[0044] 1. Select Vero cells in good growth condition. When the cells form a monolayer or reach 80%-90% confluence, discard the culture medium, wash three times with sterile PBS, and then add 1 ml of 0.25% trypsin to digest the adherent cells. After complete cell digestion, add an appropriate amount of DMEM medium containing 10% FBS, disperse the cells, and adjust the density to 5 × 10⁶ cells / cm² based on cell count. 5 Add cells / ml to a 24-well cell culture plate, 300 μL per well; incubate at 37℃ in a 5% CO2 cell culture incubator for 24 h. When the cells reach 80%-90% confluence, discard the culture medium and wash three times with sterile PBS.

[0045] 2. The serially diluted peptide 110616 was mixed with an equal volume of PEDV virus solution at MOI=0.01 and pre-incubated at 37°C for 1 hour. Then, 300 μL of each diluted peptide was added to each well of a 24-well cell culture plate, with three replicates per well. The plates were incubated at 37°C in a 5% CO2 cell culture incubator for 1 hour to allow adsorption. The infection solution was discarded, and the plates were gently washed three times with PBS buffer. 300 μL of DMEM medium containing 2% FBS was added to each well, and the plates were incubated at 37°C in a 5% CO2 cell culture incubator for 12 hours. A virus-inoculated control group without peptide and a Vero cell control group were also included.

[0046] 3. After removing the 24-well plate, discard the culture medium in each well, add 300 μL of TRIZOL to each well, let it stand for 10 min, collect the samples from each well, centrifuge at 12000 rpm and 4℃ for 10 min, and take the cell lysis supernatant for qRT-PCR detection.

[0047] The results showed that 110616 could effectively inhibit PEDV infection of Vero cells, and the inhibitory activity of 110616 against viral infection was best at a concentration of 200 μM (maximum final concentration) (see [link to study]. Figure 5 ).

[0048] Example 6: Indirect immunofluorescence identification of 110616 inhibiting PEDV infection of Vero cells

[0049] 1. Select Vero cells in good growth condition. When the cells form a monolayer or reach 80%-90% confluence, discard the culture medium, wash three times with sterile PBS, and then add 1 ml of 0.25% trypsin to digest the adherent cells. After complete cell digestion, add an appropriate amount of DMEM medium containing 10% FBS, disperse the cells, and adjust the density to 5 × 10⁶ cells / cm² based on cell count. 5 Add cells / ml to a 24-well cell culture plate, 300 μL per well; incubate at 37℃ in a 5% CO2 cell culture incubator for 24 h. When the cells reach 80%-90% confluence, discard the culture medium and wash three times with sterile PBS.

[0050] 2. The serially diluted peptide 110616 was mixed with an equal volume of PEDV virus solution at MOI=0.01 and pre-incubated at 37°C for 1 hour. Then, 300 μL of each diluted peptide was added to each well of a 24-well cell culture plate, with three replicates per well. The plates were incubated at 37°C in a 5% CO2 cell culture incubator for 1 hour to allow adsorption. The infection solution was discarded, and the plates were gently washed three times with PBS buffer. 300 μL of DMEM medium containing 2% FBS was added to each well, and the plates were incubated at 37°C in a 5% CO2 cell culture incubator for 12 hours. A virus-inoculated control group without peptide and a Vero cell control group were also included.

[0051] 3. After removing the 24-well plate, discard the culture medium in each well, gently wash three times with PBST buffer, and fix the cells with 4% paraformaldehyde solution at 4°C for 30 min.

[0052] 4. After completion, permeabilize with 0.2% Triton X-100 at room temperature for 15 minutes to promote membrane protein denaturation, thereby increasing permeability.

[0053] 5. After washing with PBST three times, add 5% skim milk blocking solution and block at 37°C for 2 hours.

[0054] 6. After washing three times with PBST, add mouse anti-PEDV N protein antibody diluted 1:1000 and incubate at 37°C for 1 hour.

[0055] 7. After washing three times with PBST, add FITC-labeled goat anti-mouse secondary antibody diluted 1:1000 and incubate at 37°C for 45 min.

[0056] 8. After washing three times with PBST, add DAPI staining solution and incubate at room temperature for 15 minutes.

[0057] 9. After washing three times with PBST, observe the results using a fluorescence inverted microscope.

[0058] The results showed that 110616 could effectively inhibit PEDV infection of Vero cells, and the inhibitory effect of 110616 on viral infection remained significant even when the concentration was reduced to 3.125 μM (see [link to study].) Figure 6 ).

Claims

1. A polypeptide that specifically binds to the S1 protein of porcine viral diarrhea virus, characterized in that, The polypeptide sequence is FWKEAK.

2. Use of the polypeptide of claim 1 in the preparation of a product for detecting and inhibiting porcine viral diarrhea virus.

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