Molecular cloning, purification and immunogenicity of recombinant Brucella abortus 544 malate dehydrogenase protein

Preparation and application of a Brucella multiepitope fusion protein based on bioinformatics and Tandem Mass Tag-based proteomics technology

Introduction

Brucellosis is a widespread zoonotic disease that poses a considerable challenge to global public health. Existing diagnostic methods for this condition, such as serological assays and bacterial culture, encounter difficulties due to their limited specificity and high operational complexity. Therefore, there is an urgent need for the development of enhanced diagnostic approaches for brucellosis.

Methods

Tandem mass tag (TMT) proteomic analysis was conducted on the wild-type strain Brucella abortus (B. abortus) DT21 and the vaccine strain B. abortus A19 to identify proteins with high expression levels. The proteins that exhibited high expression in the wild-type strain were selected based on the proteomic results. Subsequently, B-cell linear epitopes were predicted using multiple computational tools, including ABCpred, SVMTriP, BCPred, and Bepipred Linear Epitope Prediction 2.0. These epitopes were concatenated to construct a multiepitope fusion protein. Following prokaryotic expression and purification, an indirect enzyme-linked immunosorbent assay (iELISA) was developed. A total of 100 positive serum samples, 96 negative serum samples, and 40 serum samples from patients infected with other pathogens were collected and analyzed using the established iELISA. Furthermore, the protein was assessed for its capability to differentiate human brucellosis from lipopolysaccharide (LPS).

Results

Proteomic analysis revealed the presence of 152 proteins with high expression levels in the wild-type strains. A multiepitope fusion protein, comprising a total of 32 predicted B-cell linear epitopes, was successfully prepared. The results from the iELISA indicated that the multiepitope fusion protein exhibited exceptional diagnostic performance, evidenced by an area under the receiver operating characteristic curve (AUC) of 0.9576, a sensitivity of 0.9300, and a specificity of 0.8542. In comparison to the commonly utilized LPS antigen, the fusion protein demonstrated a reduced level of cross-reactivity.

Conclusions

A novel multiepitope fusion protein has been successfully developed utilizing bioinformatics and TMT proteomics technology. This fusion protein demonstrates significant potential as a diagnostic antigen for brucellosis, exhibiting high sensitivity and specificity.

Use of recombinant malate dehydrogenase (MDH) and superoxide dismutase (SOD) [CuZn] as antigens in indirect ELISA for diagnosis of bovine brucellosis

The objective of this study was to validate an indirect enzyme-linked immunoassay (iELISA) using the recombinant proteins, malate dehydrogenase (MDH) and superoxide dismutase (SOD) [CuZn], as antigens and to evaluate its ability to discriminate antibodies produced by vaccination from those induced by infection in the diagnosis of bovine brucellosis. Sera from six groups were evaluated: G1 - culture-positive animals (52 serum samples) (naturally infected); G2 - non-vaccinated animals (28 serum samples) positive in RBT (Rose Bengal test) and 2ME (2-mercaptoethanol test) selected from brucellosis-positive herds; G3 - animals from a brucellosis-free area (32 serum samples); G4 - S19 vaccinated heifers (114 serum samples); G5 - RB51 vaccinated heifers (60 serum samples); G6 - animals inoculated with inactivated Yersinia enterocolitica O:9 (42 serum samples). Diagnostic sensitivity (DSe) and diagnostic specificity (DSp) were estimated using the frequentist approach and the confidence interval (CI) (95%) calculated by the Clopper-Pearson (exact) method. The DSe for iELISA_MDH in the G1 group was 71.7% (CI 95%: 57.6-83.2%) and for the G2 100.0% (CI 95%: 87.7-100.0%), whereas the DSp was 84.4% in the G3 (CI 95%: 67.2-94.7%). For the iELISA_SOD the DSe was estimated 67.3% for the G1 (CI 95%: 52.9-79.7%) and 71.4% for G2 (CI 95%: 51.3-86.8%), while the DSp for G3 was 87.5% (CI 95%: 71.0-96.5%). iELISA_MDH and iELISA_SOD showed potential to be used in the diagnosis of infected animals, increasing the range of serological tests available for the diagnosis of bovine brucellosis, with the advantage of being S-LPS-free. However, none of the tests could differentiate between infection and vaccination.

Engineering E. coli recombinant strains for high yield production of Burkholderia pseudomallei specific antigens

A risk of introducing into the Russian Federation exotic infections including laboratory-confirmed melioidosis regularly recorded worldwide necessitates development and improvement of express diagnostics tools. Cross reactivity between phylogenetically related species of the genus Burkholderia complicates melioidosis diagnostics by express test methods based on using monoclonal antibodies against pathogen exopolysaccharide epitopes. Searching for target antigens to create the next generation group- and species-specific immunodiagnostic reagents for identifying Burkholderia pseudomallei is still of high priority. The study was aimed at cloning complete coding sequences for cell surface proteins differentiating Burkholderia pseudomallei and optimizing recombinant antigens purification protocol. In silico comparative study allowed to select highly immunogenic B. pseudomallei outer membrane proteins Omp38 and OmpA/МotB as target biomolecules. For cloning, omp38 and ompA/motB gene-specific amplicons were obtained by PCR and ligated with the linear expression vector RIC-Ready pPAL7. Competent E. coli C-Max5 cells were transformed by a ligation mixture for producing recombinant plasmids, which were further purified to transform E. coli BL21 (DE3) cells for robust recombinant protein expression. Due to a potential multimeric protein structure, a standard protein purification protocol from native cell lysate was inefficient, which was modified to increase recombinant protein yield. However, by adding denaturing conditions at intermediate purification steps caused hydrolysis of peptide bonds in the target proteins, presumably between proline and asparagine residues. As a result, N-terminal fragments connecting recombinant proteins to the stationary phase of chromatographic column were eluted and evaluated for linear epitope detection according to their molecular weights. In silico analysis data identified highly antigenic motifs within the polypeptides studied. Thus, strains of E. coli BL21(DE3) BpsOmp39 and E. coli BL21(DE3) BpsOmpА engineered by us produce cell surface proteins Omp38 and ОmpA/МotB derived from melioidosis pathogen, which can be useful for developing diagnostic test systems.

Tannic acid-mediated immune activation attenuates Brucella abortus infection in mice

Brucellosis is an emerging infectious disease affecting humans and animals. In this study, we investigated the in vitro and in vivo effects of tannic acid (TA) against Brucella abortus infection. After infection, F-actin polymerization and mitogen-activated protein kinases (MAPKs) (ERK 1/2 and p38α) phosphorylation were reduced in TA-treated cells compared with that in control cells. The mice were infected via an intraperitoneal route and were orally given TA or phosphate-buffered saline for 14 days. Spleen weights of the TA-treated and control mice were not different; however, splenic proliferation of B. abortus was significantly reduced in the TA-treated group. Immune response analysis showed that, compared with the control group, non-infected TA-treated mice displayed increased levels of interferon-γ (IFN-γ), monocyte chemoattractant protein-1 (MCP-1), and interleukin-10 at 3 days post-infection and a further increase in IFN-γ and MCP-1 at 14 days post-infection. In contrast, compared with the control group, infected TA-treated mice displayed elevated levels of IFN-γ at 3 days post-infection, which continued to increase at 14 days post-infection, as was also observed for tumor necrosis factor. Taken together, the results showing TA activation of cytokine production and inhibition of bacterial proliferation in the host highlight a potential use of TA treatment in the control of Brucella infection.

Cytokines production and toll-like receptors expression in human leukemic monocyte cells, THP-1, stimulated with Brucella abortus cellular antigens

A zoonotic pathogen, Brucella spp. is the causative agent of brucellosis, which results in abortion and loss in milk production in domestic animals, and undulant fever, osteoarticular pain and splenomegaly in humans. Due to the capability of the bacteria to modulate the host cell functions and survive in macrophages, early detection and eradication of the intracellular bacteria has received significant attention. Moreover, understanding the immunological alterations in Brucella infection is crucial to help develop control measures. Cytokines and toll-like receptors (TLRs) are some of the major compounds that play important roles in modulating the innate immunity and acquired immunity in host after infection. In this study, therefore, human leukemic monocyte cells (THP-1 cells) were stimulated with five Brucella abortus cellular components: outer membrane protein 10 (OMP10), outer membrane protein 19 (OMP19), thiamine transporter substrate-binding protein (TbpA), arginase (RocF), and malate dehydrogenase (Mdh). Post stimulation, the cytokine productions and TLR expressions in the cells were evaluated at different time points (12 h and 24 h), and analyzed using ELISA and real time RT-PCR, respectively. In the production of cytokines, it was observed that the production of TNF-α and IL-6 was highly induced in THP-1 cells stimulated with five recombinant protein antigens. Also, TLR8 was induced in a time-dependent manner after stimulation with two recombinant proteins, rOMP19 and rMdh, until 24 h. These results suggest that the two B. abortus antigens, rOMP19 and rMdh, might be involved in TLR8 signaling pathway in THP-1 cells in a time-dependent manner. These two proteins are therefore potentially effective antigen candidates which would help to provide better understandings of the immune responses after Brucella infection.

Protective efficacy of a Salmonella Typhimurium ghost vaccine candidate constructed with a recombinant lysozyme-PMAP36 fusion protein in a murine model

A Salmonella Typhimurium ghost vaccine was constructed with the use of a recombinant fusion protein consisting of lysozyme and porcine myeloid antimicrobial peptide 36 expressed by the Escherichia coli overexpression system. After confirmation of its effectiveness by transmission electron microscopy the vaccine was evaluated in a murine model. Of the 60 BALB/c mice equally divided into 4 groups, group A mice were intramuscularly inoculated with 100 μL of sterile phosphate-buffered saline, and the mice in groups B, C, and D were intramuscularly inoculated with approximately 1.0 × 10⁴, 1.0 × 10⁵, or 1.0 × 10⁶ cells of the S. Typhimurium ghost vaccine, respectively, in 100-μL amounts. The serum IgG titers against S. Typhimurium outer membrane proteins were significantly higher in groups B to D than in group A, as were the concentrations of interleukin-10 and interferon gamma in supernatants of harvested splenocytes. After challenge with wild-type S. Typhimurium, all the vaccinated groups showed significant protection compared with group A, notably perfect protection in groups C and D. Overall, these results show that intramuscular vaccination with 1.0 × 10⁵ cells of this ghost vaccine candidate provided efficient protection against systemic infection with virulent S. Typhimurium.