Functional analysis of effector of Vibrio parahaemolyticus TTSS2 on enterotoxicity.

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Many Gram-negative bacterial pathogens use a specialized Type III secretion system (TTSS) to inject virulence factors, called effectors, directly into eukaryotic cells. T3SS2, a TTSS of Vibrio parahaemolyticus which is a pathogen causing food-borne disease worldwide, is indispensable for pathogenicity, and especially enterotoxicity, of this bacterium. However, which effector(s) is or are responsible for the T3SS2-dependent enterotoxicity has remained an open question. In this study, we identified a novel effector, VopE, as a major contributor to the enterotoxicity of Vibrio parahaemolyticus in the rabbit ileal loop test. The VopE protein consists of three domains, the N-terminal, the long repeat (LR), and the C-terminal domains. The LR domain contains three types of repeat units. We demonstrated that VopE directly binds to F-actin via a repeat unit (rep1) in the LR or the C-terminal domain, and that the enterotoxic activity generated by VopE correlated significantly with its F-actin binding activity. We further demonstrated that a TTSS2-related TTSS and a vopE homologous gene in a non-O1/non-O139 V. cholerae strain, which is pathogenic for humans, were also involved in the enterotoxicity of the strain. These results indicate that VopE is a novel F-actin-targeting effector and its ability to bind to F-actin is involved in the enterotoxic activity of TTSS2-possessing pathogens.