Identification of Two Translocon Proteins of Vibrio parahaemolyticus Type III Secretion System 2

Abstract

The type III secretion system (T3SS) translocon complex is composed of several associated proteins, which form a translocation channel through the host cell plasma membrane. These proteins are key molecules that are involved in the pathogenicity of many T3SS-positive bacteria, because they are necessary to deliver effector proteins into host cells. A T3SS designated T3SS2 of Vibrio parahaemolyticus is thought to be related to the enterotoxicity of this bacterium in humans, but the effector translocation mechanism of T3SS2 is unclear because there is only one gene (the VPA1362 gene) in the T3SS2 region that is homologous to other translocon protein genes. It is also not known whether the VPA1362 protein is functional in the translocon of T3SS2 or whether it is sufficient to form the translocation channel of T3SS2. In this study, we identified both VPA1362 (designated VopB2) and VPA1361 (designated VopD2) as T3SS2-dependent secretion proteins. Functional analysis of these proteins showed that they are essential for T3SS2-dependent cytotoxicity, for the translocation of one of the T3SS2 effector proteins (VopT), and for the contact-dependent activity of pore formation in infected cells in vitro. Their targeting to the host cell membrane depends on T3SS2, and furthermore, they are necessary for T3SS2-dependent enterotoxicity in vivo. These results indicate that VopB2 and VopD2 act as translocon proteins of V. parahaemolyticus T3SS2 and hence have a critical role in the T3SS2-dependent enterotoxicity of this bacterium.

Effect on Human Cells of Environmental Vibrio parahaemolyticus Strains Carrying Type III Secretion System 2

“…(ii) Two strains (VPe23 and VPe28, both tdh negative and trh negative) representing strains containing T3SS2 genes such as vopB2 and vscC2, encoding translocation proteins (10,26), vopT and vopP, encoding effector proteins (9,26), and other genes located on the pathogenicity island (VP-PAI), such as vopC, encoding a gene homologous to the Escherichia coli cytotoxic necrotizing factor, and VPA1376, encoding a protein homologous to Vibrio cholerae VPI protein (12).…”

“…These data, together with other data obtained in recent years (12,19,28), indicated that TDH or TRH is not the only bacterial factor determining V. parahaemolyticus virulence and that other factors might contribute to the pathogenic potential directed to human hosts. A number of these factors have been subsequently detected and well characterized (10,12,20,28). Genome sequencing of the V. parahaemolyticus clinical strain RIMD2210633 revealed that this bacterial species possesses two sets of type 3 secretion system (T3SS) genes: T3SS1, located on chromosome 1, and T3SS2, located on chromosome…”

“…T3SS1 genes display high similarity with those from Yersinia T3SS, while T3SS2 genes are only partially similar to other bacterial secretion systems reported to date (20). Following this discovery, a number of studies have been conducted to elucidate the role of these genes in the pathogenicity process (1,9,10,20). Using in vitro human cell lines and ileal loop tests, it was shown, using clinical strains, that T3SS1 is responsible for the cytotoxicity of V. parahaemolyticus for eukaryotic cells (20) while T3SS2 is involved in cytotoxicity and enterotoxicity (9,20).…”

Diarrhea induced by infection of <I>Vibrio parahaemolyticus</I>

“…T3SS2 is found only in Kanagawa phenomenon (KP)-positive strains and produces enterotoxicity that can be assayed using the rabbit ileal loop model (29). Recently, Kodama et al identified two T3SS2 translocon proteins (VopB2, VopD2) ; translocon deletion strains lack the ability to cause fluid accumulation (30). Those studies strongly imply T3SS2 involvement in the enterotoxicity of V. parahaemolyticus and, consequently, the production of Vp-induced diarrhea.…”

Antibiotic-Resistance Profiles and the Identification of the Ampicillin-Resistance Gene of Vibrio parahaemolyticus Isolated from Seawater

“…독 (TDH-related hemolysin, TRH), serine protease 및 type III secretion systems (TTSS1과 2)를 통해 분비되는 각종 effector 단백질 등이 보고되어 있으나 정확한 병원성 기작에 관한 설명은 아직도 많이 부족한 실정이다 (Honda and Iida, 1993;Lee et al, 2002;Makino et al, 2003;Park et al, 2004;Kodama et al, 2007;Kodama et al, 2008).…”