Role of the TPR family protein VPA1365 in regulating type III secretion system 2 and virulence in <i>Vibrio parahaemolyticus</i>

The type III secretion system 2 (T3SS2) is of crucial significance for the pathogenicity of <i>Vibrio parahaemolyticus</i>; nevertheless, the biological functions of many genes within the T3SS2 gene cluster and the transcriptional regulatory network of T3SS2 remain ambiguous. In this study, we identified VPA1365, a tetratricopeptide repeat family regulator encoded in the T3SS2 gene cluster, which differs from other known T3SS2 regulatory factors, such as OmpR, ToxR, or LysR family proteins. VPA1365 not only positively regulated the expression and secretion of T3SS2-related proteins but also enhanced the virulence in infant rabbits and zebrafish. Moreover, we identified several novel functions of VPA1365, such as its contribution to hemolytic activity, biofilm formation, cytotoxicity, and adhesion ability, uncovering its global physiological role in <i>V. parahaemolyticus</i>. The putative VPA1365-binding site was predicted and identified through the MEME-Suite tool and electrophoretic mobility shift analysis. Collectively, these results broaden our understanding of the regulatory pathways of T3SS2 and virulence.