Functional characterization of MMAR_1296 in Mycobacterium marinum and its potential as a vaccine candidate.

The Pro-Glu/Pro-Pro-Glu (PE/PPE) family proteins in mycobacteria plays a crucial role in pathogenesis and immune evasion. These proteins characterized by unique structures with conserved sequences. This study elucidated the specific immunological functions of MMAR_1296 from marine mycobacterium. Expressing MMAR_1296 in Mycobacterium smegmatis (M. smegmatis) led to significant alterations in bacterial morphology, as well as reduced survival of M. smegmatis under adverse in vitro conditions and within macrophages. Furthermore, transcriptome analysis of mouse macrophages indicated that natural immunity-related pathways were upregulated in the group infected with M. smegmatis recombinantly expressing MMAR_1296. Moreover, the mycobacterium Growth Inhibition Assays(MGIA)in mice demonstrated that M. smegmatis expressing MMAR_1296 exerted a significant inhibitory effect against Mycobacterium abscessus (M. abscessus) and Mycobacterium marinum (M. marinum) infections. Immunization challenge experiments in mice further confirmed its protective effects, showing a reduction in organ bacterial loads by 1 log value compared to the positive control group. These findings indicate that MMAR_1296 is a promising vaccine candidate for M. abscessus and M. marinum. Given that PE/PPE protein family is also a crucial component of Mycobacterium tuberculosis (M. tuberculosis) antigens, further exploration of sequence functions based on MMAR_1296 could reveal broader applications of PE/PPE proteins family for M. tuberculosis treatment. This study supported vaccine development targeting PE/PPE proteins in mycobacteria and paves the way for broader applications.