Screening and comparison of differentially expressed genes between one MDR-TB strain and the virulent M. tuberculosis H37Rv

Improvement of the immunogenicity of ESAT-6 via fusion with the dodecameric protein dodecin of Mycobacterium tuberculosis

Tuberculosis (TB) is a chronic infectious disease that creates a heavy medical burden worldwide. The only approved vaccine, Bacillus Calmette-Guérin (BCG), cannot fully protect adolescents and adults from TB. Therefore, there is an urgent need to develop an effective new vaccine. Previous studies have found that dodecin, a flavin-binding protein of Mycobacterium tuberculosis (Mtb), can form stable dodecamers and has the potential to improve the immunogenicity of Mtb antigens. In this study, we constructed the fusion protein dodecin-ESAT-6 and evaluated the immunogenicity of dodecin, ESAT-6, and dodecin-ESAT-6 separately. Our results showed that dodecin-ESAT-6 is a dodecameric protein that can withstand heat at 95 °C and under SDS-PAGE conditions. Dodecin-ESAT-6 increased the expression of the costimulatory molecules CD80, CD86, and major histocompatibility complex class II (MHC-II) on the surface of RAW264.7 macrophages. Mice immunized with dodecin-ESAT-6 exhibited higher percentages of antigen-specific CD4⁺ and CD8⁺ T lymphocytes, higher levels of spleen lymphocyte proliferation and IFN-γ and IL-2 secretion, and a lower level of IL-4 secretion than those immunized with ESAT-6. The IgG, IgG1, and IgG2a titers of the dodecin-ESAT-6 group were significantly higher than those of the ESAT-6 group. Dodecin-ESAT-6 elicited a high IgG2a/IgG1 ratio and tended to produce a predominantly Th1-like response. These results support the conclusion that the dodecin-ESAT-6 dodecameric protein induced strong Th1 immune responses and improved the immunogenicity of ESAT-6, which provides a new strategy for TB vaccine development.

Flavin Storage and Sequestration by Mycobacterium tuberculosis Dodecin

Dodecins are small flavin binding proteins occurring in archaea and bacteria. They are remarkable for binding dimers of flavins with their functional relevant aromatic isoalloxazine rings deeply covered. Bacterial dodecins are widely spread and found in a large variety of pathogens, among them Pseudomonas aeruginosa, Streptococcus pneumonia, Ralstonia solanacearum, and Mycobacterium tuberculosis ( M. tuberculosis). In this work, we seek to understand the function of dodecins from M. tuberculosis dodecin. We describe flavin binding in thermodynamic and kinetic properties and achieve mechanistic insight in dodecin function by applying spectroscopic and electrochemical methods. Intriguingly, we reveal a significant pH dependence in the affinity and specificity of flavin binding. Our data give insight in M. tuberculosis dodecin function and advance the current understanding of dodecins as flavin storage and sequestering proteins. We suggest that the dodecin in M. tuberculosis may specifically be important for flavin homeostasis during the elaborate lifestyle of this organism, which calls for the evaluation of this protein as drug target.

The novel gene mtb192 is a candidate marker for the detection of multidrug-resistant Mycobacterium tuberculosis strains

BACKGROUND

Multi-drug resistant tuberculosis (TB) is one of the most main threats to the global TB control work at present. And it's very difficult to detect. From a screen of differentially expressed genes in multidrug-resistant tuberculosis (MDR-TB) strains, we identified a new gene, mtb192. In the present study, we verified the association of mtb192 with TB drug resistance by detecting its expression in clinical isolates from paediatric TB patients.

MATERIALS AND METHODS

The homology of mtb192 was analysed by gene blasting in GenBank. The drug resistance of clinical TB isolates was tested, and mtb192 gene expression was compared using reverse transcription polymerase chain reaction (RT-PCR) and quantitative PCR.

RESULTS

Gene homology suggested that mtb192 is a new gene sequence. Among the 120 clinical isolates, 14 were positive for mtb192, including 12 in the MDR group, 2 in the single drug-resistant group, 1 in the poly-resistant group, and 1 in the sensitive group. The mtb192 positive expression rate was significantly higher in the MDR group than all other groups, and the mtb192 mRNA expression level was significantly higher in the MDR group than in the non-MDR group.

CONCLUSIONS

The new gene mtb192 showed significantly higher expression in MDR-TB strains and could be related to the development of MDR in Mycobacterium tuberculosis, highlighting it as a new genetic marker in the detection of MDR-TB.