Mycobacterium tuberculosis PPE18-LS protein nanoparticle as well as preparation method and application thereof

Abstract

The invention is applicable to the field of gene engineering, and provides a mycobacterium tuberculosis PPE18-LS protein nanoparticle, a preparation method and application thereof, the mycobacterium tuberculosis PPE18-LS protein nanoparticle is formed by sequence fusion of mycobacterium tuberculosis PPE18 protein and LS protein, and the amino acid sequence of the mycobacterium tuberculosis PPE18-LS protein nanoparticle is shown as SEQ ID NO: 2 in a sequence table. According to the invention, the key protective antigen PPE18 of mycobacterium tuberculosis and the LS protein with self-assembly characteristic are subjected to fusion expression, and the PPE18-LS protein nanoparticles with uniform structure are successfully prepared through an Escherichia coli expression system. In-vivo experiment results show that the PPE18-LS protein nanoparticles can effectively activate response pathways of humoral immunity and cellular immunity of a host, show obvious protective efficacy in a mouse model, provide an important technical path for developing a new generation of tuberculosis preventive vaccines, and have wide clinical application prospects and industrialization values.

Description

Technical Field

[0001] This invention belongs to the field of genetic engineering, and in particular relates to a Mycobacterium tuberculosis PPE18-LS protein nanoparticle, its preparation method and its uses. Background Technology

[0002] Tuberculosis (TB) is a disease caused by Mycobacterium tuberculosis (Mycobacterium tuberculosis). Mycobacterium tuberculosis, M.tb Tuberculosis, a chronic infectious disease caused by tuberculosis, has been listed by the World Health Organization as one of the top ten causes of death worldwide. Although the BCG vaccine has shown significant effectiveness in preventing severe tuberculosis such as tuberculous meningitis in children, its protective efficacy against adult pulmonary tuberculosis is only 0-80%, particularly in areas with high tuberculosis prevalence. Even more serious is the fact that the recent prevalence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) poses unprecedented challenges to existing prevention and control systems.

[0003] PPE18 antigen belongs to the PPE protein family, which is unique to Mycobacterium tuberculosis. This antigen can effectively activate the antigen presentation function of dendritic cells and significantly promote the secretion of Th1 cytokines such as IFN-γ.

[0004] Therefore, there is an urgent need to develop a new generation of highly effective vaccines against tuberculosis. Summary of the Invention

[0005] The purpose of this invention is to provide Mycobacterium tuberculosis PPE18-LS protein nanoparticles, aiming to solve the problems mentioned in the background art.

[0006] To address the above problems, the present invention provides a Mycobacterium tuberculosis PPE18-LS protein nanoparticle, which is formed by the fusion of Mycobacterium tuberculosis PPE18 protein and LS protein through sequence, and its amino acid sequence is shown in SEQ ID NO:2.

[0007] Another object of the present invention is to provide a gene encoding the above-mentioned Mycobacterium tuberculosis PPE18-LS protein nanoparticles, the nucleotide sequence of which is shown in the sequence listing SEQ ID NO:1.

[0008] Another object of the present invention is to provide a recombinant expression vector comprising the above-described coding gene.

[0009] Another object of the present invention is to provide a host cell comprising at least one of the above-mentioned Mycobacterium tuberculosis PPE18-LS protein nanoparticles, the above-mentioned encoding gene, and the above-mentioned recombinant expression vector.

[0010] Another object of the present invention is to provide a method for preparing the above-mentioned Mycobacterium tuberculosis PPE18-LS protein nanoparticles, which includes the following steps: The coding gene with the nucleotide sequence shown in SEQ ID NO:1 was inserted into the expression vector to construct the recombinant expression vector. The recombinant expression vector was transformed into host cells for induced expression, and then the protein was purified to obtain the Mycobacterium tuberculosis PPE18-LS protein nanoparticles.

[0011] Another object of the present invention is to provide the use of the above-mentioned Mycobacterium tuberculosis PPE18-LS protein nanoparticles, or the above-mentioned encoding gene, or the above-mentioned recombinant expression vector, or the above-mentioned host cell in the preparation of drugs or vaccines for the prevention and treatment of tuberculosis.

[0012] Another object of the present invention is to provide a drug or vaccine for the prevention and treatment of tuberculosis, comprising a pharmaceutically acceptable carrier and the aforementioned Mycobacterium tuberculosis PPE18-LS protein nanoparticles.

[0013] This invention provides a Mycobacterium tuberculosis PPE18-LS protein nanoparticle, which employs multi-fragment immunogenic protein fusion to induce a synergistic immune effect and significantly enhance the antigen's immunostimulatory capacity. This PPE18-LS protein nanoparticle is non-toxic and non-pathogenic, ensuring good biosafety for vaccines and making it suitable for clinical application. Animal experiments show that this PPE18-LS protein nanoparticle can simultaneously activate high levels of humoral immunity (IgG antibody response) and cellular immunity, exhibiting significant protective immune effects in animals. The PPE18-LS protein nanoparticle provided by this invention not only offers a new technical route for the development of tuberculosis vaccines, but its modular design concept can also be extended to the development of vaccines for other important infectious diseases. This technology has been validated through multiple experiments, demonstrating promising translational applications and laying a solid foundation for subsequent preclinical research and industrialization development. Attached Figure Description

[0014] Figure 1 This is a diagram showing the double enzyme digestion identification of the recombinant expression vector; Figure 2 SDS-PAGE image of PPE18-LS protein nanoparticles for expression and purification; Figure 3 Western blot identification of PPE18-LS protein nanoparticles; Figure 4 Electron micrograph of PPE18-LS protein nanoparticles; Figure 5Serum ELISA results of mice immunized with PPE18-LS protein nanoparticles; Figure 6 The results of spleen lymphocyte index detection in mice after immunization with PPE18-LS protein nanoparticles; Figure 7 The results of serum IFN-γ detection in mice after immunization with PPE18-LS protein nanoparticles. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] This invention innovatively employs Lumazine Synthase (LS) protein, derived from hyperthermophilic bacteria, as a vaccine carrier platform. This LS protein possesses unique self-assembly properties, capable of forming an icosahedral symmetric structure with a diameter of approximately 15 nm under physiological conditions, displaying up to 60 antigenic epitopes on its surface. By fusing the LS protein with Mycobacterium tuberculosis protective antigen using genetic engineering techniques, a nanoparticle vaccine with high structural stability and immunogenicity can be successfully constructed.

[0017] The embodiments of the present invention achieve a high-density ordered arrangement of antigens by fusing PPE18 with LS protein, which not only greatly improves the immunogenicity of antigens, but also overcomes the technical bottleneck of low delivery efficiency of traditional subunit vaccines.

[0018] Specifically, in one embodiment of the present invention, a Mycobacterium tuberculosis PPE18-LS protein nanoparticle is provided, which is formed by the fusion of the C-terminus (32C) of the Mycobacterium tuberculosis MTB32A protein, the PPE18 protein and the LS protein through sequence. Preferably, the C-terminus carries the LS protein sequence and adds a His6 tag. The amino acid sequence of the PPE18-LS protein nanoparticle is shown in SEQ ID NO:2 of the sequence listing.

[0019] In another embodiment of the present invention, a method for preparing the above-mentioned Mycobacterium tuberculosis PPE18-LS protein nanoparticles is also provided, which includes the following steps: S1. Insert the coding gene with the nucleotide sequence shown in SEQ ID NO:1 into the expression vector to construct the recombinant expression vector; S2. The recombinant expression vector is transformed into host cells for induced expression, and then purified to obtain the Mycobacterium tuberculosis PPE18-LS protein nanoparticles.

[0020] In practical applications, the expression vector is pET28a(+), which can be expressed in prokaryotic cells, preferably containing the T7 promoter; the host cell is Escherichia coli, preferably Escherichia coli BL21.

[0021] In this embodiment of the invention, mice were immunized with the prepared PPE18-LS protein nanoparticles, and antibody levels in the mice were measured periodically to evaluate the immunogenicity of the PPE18-LS protein nanoparticles. In another embodiment of the present invention, a drug or vaccine for the prevention and treatment of tuberculosis is also provided, comprising a pharmaceutically acceptable carrier and the aforementioned Mycobacterium tuberculosis PPE18-LS protein nanoparticles. In practical applications, the vaccine is a nanoparticle vaccine.

[0022] Example 1: This example provides a method for the expression and purification of Mycobacterium tuberculosis PPE18-LS protein nanoparticles, specifically including the following steps: The PPE18 gene was selected from GenBank (NC_000962.3), and the PPE18-LS coding gene (nucleotide sequence shown in SEQ ID NO:1) was designed as the target gene. Nde I and Hind The target gene was constructed into pET28a(+) (Invirogen, USA) by restriction enzyme III, resulting in a recombinant expression vector. 50 μL of *E. coli* BL21(DE3) competent cells (Invitrogen, USA) were added, along with 5 μL of the recombinant expression vector. The cells were incubated on ice for 30 minutes, followed by a 90-second heat shock, and then another 3 minutes on ice. 500 μL of antibiotic-free LB broth was added, and the cells were incubated at 37°C and 180 rpm with shaking for 45 minutes. 100 μL of the recombinant vector was plated on LB agar plates containing 100 μg / mL Kans and incubated overnight at 37°C. Three positive clones were picked the following day and sent to Anhui General Biotechnology Co., Ltd. for sequencing verification. The correctly recombinant strain was named pET28a(+)-PPE18-LS. The recombinant expression vector was then further processed. Apa I and Xho Double enzyme digestion identification, results as follows Figure 1 As shown, the size of the target band is consistent with expectations, and the recombinant expression vector was successfully constructed.

[0023] A single recombinant positive clone was picked and inoculated into LB liquid medium and cultured overnight with shaking at 37°C and 180 rpm. The overnight culture was then inoculated into fresh LB medium at a 1:100 ratio and cultured until the bacterial OD reached the target value. 600When the bacterial count reached 0.6-0.8, IPTG was added to a final concentration of 1 mmol / L to induce expression for 3 hours. The cells were then collected by centrifugation at 12000 rpm for 10 minutes and resuspended in 20 mM Tris-HCl buffer. After sonication for 50 minutes, the cells were centrifuged at 12000 rpm for 20 minutes at 4°C, the supernatant was discarded, and the precipitate was washed. The precipitate was dissolved in 8 M urea and centrifuged again at 12000 rpm for 20 minutes at 4°C, and the supernatant was collected. The supernatant was placed in a dialysis bag with a molecular weight cutoff of 3.5 kDa for dialysis refolding. After dialysis, the cells were filtered through a 0.22 μm pore size membrane to remove residual particulate impurities. The filtrate was then used for protein purification on a Ni-NTA affinity column. The imidazole elution peak protein was harvested and subjected to SDS-PAGE electrophoresis. The presence of the target band on the PAGE gel indicated that the purified protein was a recombinant protein, denoted as PPE18-LS protein nanoparticles. Figure 2 As shown.

[0024] Example 2: This example describes a Western blot identification experiment for protein nanoparticles. The specific steps are as follows: Bacterial cells induced in Example 1 were ultrasonically disrupted and centrifuged. Soluble or inclusion body protein samples were collected. Quantitative protein loading of 20-30 μg per well was performed, followed by 12% SDS-PAGE electrophoresis. After electrophoresis, the protein was transferred to a PVDF membrane (0.45 μm) and blocked at room temperature for 1 hour using 5% skim milk powder or BSA in TBST buffer. Primary antibody (such as anti-His tag antibody or specific anti-MTB protein antibody) was then added at the recommended dilution and incubated overnight at 4°C. The next day, the membrane was washed three times with TBST for 10 minutes each time, and HRP-labeled secondary antibody was added, followed by incubation at room temperature for 1 hour. After washing again, ECL chemiluminescent substrate was added, and the target protein bands were detected using a gel imaging system. Figure 3 As shown in the figure. The results indicate that all PPE18-LS protein nanoparticles can be specifically recognized by His antibodies.

[0025] Example 3: This example describes an electron microscopy observation experiment of protein nanoparticles, as follows: 10 μL of purified PPE18-LS protein nanoparticle solution was dropped onto the surface of a carbon film copper mesh and allowed to stand at room temperature for 1 minute to allow for particle adsorption. After gently absorbing excess liquid with filter paper, 10 μL of 2% sodium phosphotungstenate (pH=7.0) or 2% uric anhydride was immediately added as a negative stain and stained for 30 seconds. The stain was then absorbed again with filter paper and allowed to air dry at room temperature. The dried sample was then imaged under a transmission electron microscope (e.g., TEM, 80 kV). Figure 4 As shown. Figure 4The distribution and morphology of the protein nanoparticles were observed. The PPE18-LS protein nanoparticles exhibited a highly uniform particle size distribution, with a regular surface topology and stable tertiary structure.

[0026] Example 4: This example is a mouse immunization experiment, specifically as follows: Thirty-six 6-week-old female BALB / c mice were randomly divided into the following three groups (n=12 per group): 1. PBS control group; 2. BCG vaccine group; 3. PPE18-LS protein nanoparticle group. All groups underwent subcutaneous injection at multiple sites, with three immunizations administered on days 0, 14, and 28. Each mouse in the PBS group received 200 μL of PBS; each mouse in the BCG group received 2 × 10⁻⁶ PPE18-LS protein nanoparticles. 5 CFU BCG vaccine; each mouse in the PPE18-LS protein nanoparticle group was injected with 30 μg of PPE18-LS protein nanoparticles. Serum samples were collected by ocular blood sampling on days 0, 7, 14, 21, 28, 35, and 42 post-immunization. On days 35 and 42, four mice from each group were randomly selected for ocular blood sampling and spleen collection for subsequent spleen lymphocyte proliferation assays.

[0027] I. Antibody Level Detection: The level of specific IgG antibodies against the antigen in the serum of immunized mice was detected using an indirect ELISA method. 100 μL of recombinant antigen diluted with 0.1 M carbonate buffer (pH=9.6) at a concentration of 1-2 μg / mL was added to each well of a 96-well ELISA plate and incubated overnight at 4°C. The next day, the coating solution was discarded, and the plate was washed three times with PBST (PBS + 0.05% Tween-20) for 5 minutes each time. Then, 200 μL of 5% BSA blocking buffer was added to each well, and the plate was blocked at 37°C for 1 hour. After blocking, the plate was washed again, and 100 μL of mouse serum sample diluted 1:10000 was added to each well, and the plate was incubated at 37°C for 1 hour. After washing, HRP-labeled anti-mouse IgG secondary antibody (dilution ratio 1:5000) was added, and the plate was incubated at 37°C for 1 hour. After washing, TMB substrate solution was added, and the plate was developed in the dark for 15 minutes. The reaction was stopped with stop solution, and the absorbance (OD) was read at 450 nm. 450 The result is as follows: Figure 5 As shown, the PPE18-LS protein nanoparticle vaccine can significantly induce high levels of antigen-specific IgG antibody production (3-5 times higher than the control group, p<0.01) and significantly enhance the antibody response against antigen-specific antibodies. M.tb Specific humoral immune response.

[0028] II. Splenic Lymphocyte Proliferation Assay: Mice were sacrificed on day 35 or 42 post-immunization. The spleen was aseptically removed and placed in a culture dish containing RPMI-1640 medium. The spleen was ground using a sterile syringe plunger to prepare a single-cell suspension. After filtration through a 70 μm cell sieve, red blood cells were removed with erythrocyte lysis buffer. The cells were washed twice with PBS and finally resuspended in RPMI-1640 complete medium containing 10% fetal bovine serum (FBS) and 1% penicillin-streptomycin. The cell concentration was adjusted to 2 × 10⁶ cells / mL. 6 per mL.

[0029] 100 μL of cell suspension was added to a 96-well cell culture plate, with 3 replicates per group. Antigen (final concentration 5 μg / mL) was added for stimulation, with the culture medium serving as a blank control. After incubating the cells at 37°C and 5% CO2 for 42 hours, 10 μL of CCK-8 reagent was added to each well, and incubation continued for another 4 hours. The absorbance (OD) of each well was then read using a microplate reader at 450 nm. 450 Cell proliferation capacity was assessed using the stimulation index (SI = experimental group OD / control group OD). Results are as follows: Figure 6 As shown, there was no significant difference in the stimulation index between the PBS and BCG groups at 35 and 42 days (P > 0.05), and the proliferation level of splenic lymphocytes remained basically stable. The stimulation index of PPE18-LS protein nanoparticles was 1.65, which significantly enhanced the ability of splenic lymphocytes to proliferate.

[0030] III. Serum Cytokine Level Analysis: Serum was collected from mice on days 21 and 42 post-immunization via tail docking. The serum was separated by centrifugation at 3000 rpm for 10 minutes, and the supernatant was stored at -80℃. The levels of IFN-γ cytokines in the serum were quantitatively detected using a commercial ELISA kit. Following the kit instructions, the pre-coated antibody-containing 96-well plates were equilibrated at room temperature. Standards and diluted serum samples (100 μL per well) were added, and the plates were incubated at 37℃ for 2 hours. After discarding the liquid, the plates were washed 5 times, and biotin-labeled detection antibody was added. The plates were incubated at 37℃ for 1 hour, washed again, and HRP enzyme conjugate was added. The plates were incubated at room temperature for 30 minutes. After washing, TMB substrate was added for color development. After 15 minutes of reaction, stop solution was added, and the absorbance was read at 450 nm using a microplate reader. The concentration of cytokines in the samples was calculated based on the standard curve. Results are shown below. Figure 7 As shown, the PPE18-LS protein nanoparticle vaccine can significantly enhance IFN-γ secretion levels, effectively induce Th1 immune responses, and establish durable anti-tuberculosis immune protection for the host.

[0031] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A Mycobacterium tuberculosis PPE18-LS protein nanoparticle, characterized in that, It is formed by the fusion of Mycobacterium tuberculosis PPE18 protein and LS protein, and its amino acid sequence is shown in SEQ ID NO:2 of the sequence listing.

2. The encoding gene of the Mycobacterium tuberculosis PPE18-LS protein nanoparticle as described in claim 1, characterized in that, The nucleotide sequence of the encoding gene is shown in the sequence listing SEQ ID NO:

1.

3. A recombinant expression vector, characterized in that, It includes the coding gene as described in claim 2.

4. A host cell, characterized in that, It comprises at least one of the following: the Mycobacterium tuberculosis PPE18-LS protein nanoparticles of claim 1, the encoding gene of claim 2, and the recombinant expression vector of claim 3.

5. A method for preparing Mycobacterium tuberculosis PPE18-LS protein nanoparticles as described in claim 1, characterized in that, Includes the following steps: The coding gene with the nucleotide sequence shown in SEQ ID NO:1 was inserted into the expression vector to construct the recombinant expression vector. The recombinant expression vector was transformed into host cells for induced expression, and then the protein was purified to obtain the Mycobacterium tuberculosis PPE18-LS protein nanoparticles.

6. The use of the Mycobacterium tuberculosis PPE18-LS protein nanoparticle as described in claim 1, or the encoding gene as described in claim 2, or the recombinant expression vector as described in claim 3, or the host cell as described in claim 4 in the preparation of drugs or vaccines for the prevention and treatment of tuberculosis.

7. A drug or vaccine for the prevention and treatment of tuberculosis, comprising a pharmaceutically acceptable carrier, characterized in that, It also includes the Mycobacterium tuberculosis PPE18-LS protein nanoparticles as described in claim 1.

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