VopV, an F-Actin-Binding Type III Secretion Effector, Is Required for Vibrio parahaemolyticus-Induced Enterotoxicity

Hirotaka Hiyoshi et al. Cell Host & Microbe 10, 401–409, October 20, 2011

Speaker: Chung-Han Hsieh (謝宗翰)                           Time: 15:00~16:00, Mar. 21, 2012

Commentator: Dr. Jiunn-Jong Wu (吳俊忠博士) Place: Room 601

Abstract:

Vibrio parahaemolyticus is a gram-negative halophilic bacterium which causes diarrhea and other gastroenteric symptoms after we eat the contaminated seafood. Most clinical isolates showβ-hemolysis while the environmental strains barely do so. This hemolysis is called Kanagawa phenomenon (KP), and is a very useful mark for identifying the pathogenic strains. The whole genome sequence of a KP-positive strain shows that this strain contains two sets of gene clusters of type III secretion system, namely TTSS1 and TTSS2. TTSS1 is also found in the KP–negative strains and known to be involved in cytotoxicity and induction of autophagy. TTSS2 is found only in the KP-positive strains and is involved in enterotoxicity in the rabbit ileal loop. Many effectors of TTSS2 have been identified. But, the authors found that these factors did not play important roles inenterotoxicity, meaning that one or more unknown factors may be involved in this property. The authors analyzed the secretome of V. parahaemolyticus with or without TTSS2 by SDS-polyacrylamide gel electrophoresis, and they found differential expression of a protein of about 235 kDa. The result of N-terminal identification showed that this protein is a novel protein, designated VopV, with partial homology to an effector, VopM, produced by non-O1/non-O139 V. cholerae. Both the rabbit ileal loop test and histology of V. parahaemolyticus-infected rabbit intestinal loop revealed thatVopV is highly associated with enterotoxicity. In a pull-down assay, VopV exhibited the actin-binding and actin-bundling activities. There are three domains in VopV designated N, long repeat (LR) and C. The authors then isolated several truncated VopV mutants to determine which of these domains may contribute to the actin-binding and actin-bundling activity. The results showed that both the LR and C domains could bind actin, but only the rep1 units of LR domain possessed the actin-bundling ability. The authors then demonstrated that the enterotoxicity correlated with actin-bundling, but not actin-binding ability. Lastly, the authors showed that the VopM protein in non-O1/non-O139 V. cholerae also played an important role in enterotoxicity. This study not only found an important enteropathogenic factor in V. parahaemolyticus but also explained why the non-O1/non-O139 V. cholerae could also cause enteric symptoms.

References:

1.       Hiyoshi, H., Kodama, T., Iida, T., and Honda, T. (2010). Contribution of Vibrio parahaemolyticus virulence factors to cytotoxicity, enterotoxicity, and lethality in mice. Infect. Immun. 78, 1772–1780.

2.       Park, K.S., Ono, T., Rokuda, M., Jang, M.H., Okada, K., Iida, T., and Honda, T.(2004). Functional characterization of two type III secretion systems of Vibrio parahaemolyticus. Infect. Immun. 72, 6659–6665.