The Effect of Single Amino Acid Substitution in SecA2 on Protein Translocation and Pathogenicity of Listeria monocytogenes

Listeria monocytogenes is an important zoonotic pathogen that cause severe listeriosis with high mortality in immunosuppressive humansinfection and pathogenicity of L. monocytogenes was mediated by several surface proteins that translocated by secretion systems. Our previous genomic study showed the secretion systems of the virulent and low-virulent strains were different in secA2 and two hollin genes. To confirm whether the pathogenicity of the two strains was determined by the difference observed in secretion system. We deleted secA2 and the two hollin genes to compare the pathogenic phenotypes. Our data showed that secA2 but not the two hollin genes affected the pathogenic phenotypes. To further confirm whether the single base mutant in secA2 affected the protein pathogenicity and translocation ability of SecA2, we complemented the secA2 deletion mutant strain with secA2(Lm850658) and secA2(M7), which encode SecA2 with Asn567 and Lys567, respectively. Our data showed that secA2 mutant complement with secA2(Lm850658) instead of secA2(M7) significantly improved the adhesion and invasion ability to epithelial cells Caco-2 and bacterial load in mice liver and spleen at both 24 and 48 h post infection. Cell surface protein analysis indicated that only SecA2 with Asn567 could restore the protein translocation ability. Taken together, our study demonstrated that single amino acid mutant in SecA2 affected the protein translocation and pathogenicity of L. monocytogenes for the first time.