All data are expressed as the means and standard deviations of three determinations per experimental condition. Statistical significance was determined using a one-way anova followed by Dunnett’s multiple comparison test. A P-value < 0.05 was considered statistically significant. The T3SS-associated chaperone and the effector complex

bind to each other with high affinity (Luo et al., 2001). Therefore, we used selleck chemical a screening assay using T3SS2 effectors fused with GST to pull down chaperone candidates. The amino-terminal regions of T3SS2 effectors (VopC, VopL, VopP, and VopT) fused to the CyaA (Bordetella pertussis toxin) catalytic domain can be injected into host cells (Kodama et al., 2007) (T. Kodama, unpublished data). This is consistent with other T3SS effectors and suggests that the amino-terminal regions of V. parahaemolyticus T3SS2 effectors are sufficient for efficient secretion and translocation. In general, amino-terminal domains (1–200 amino acids) of T3SS effectors contain the amino-terminal secretion signal of the T3SS and the chaperone-binding domains, which are both essential for effector secretion

(Feldman & Cornelis, 2003; Parsot et al., 2003). Plasmids expressing the PD-332991 amino-terminal domains (1–200 amino acids) of the T3SS2 effectors VopC, VopL, VopP, and VopT fused to GST were introduced into V. parahaemolyticus knockout strains for each gene. The GST fusions expressed in V. parahaemolyticus strains were purified using glutathione beads and separated using SDS-PAGE. The molecular weights of most T3SS-associated chaperones are less than 20 kDa (Feldman & Cornelis, 2003;

Parsot et al., 2003); therefore, the areas containing proteins of these molecular weights were carefully observed. Although the T3SS2 effectors fused to GST appeared to be unstable (a lower amount of T3SS2 effector fusions than breakdown products was observed), the amino-terminal 1–200 amino acids of the T3SS2 effectors fused to GST were copurified with a specific band that was not observed in the negative control (GST alone), as shown in Fig. 1a. Mass analysis revealed proteins interacting with GST–VopC1–200, GST–VopL1–200, and GST–VopT1–200 (Fig. 1b), while GST–VopP1–200 did not interact with any specific proteins that could be chaperone candidates. The results suggested that only one protein encoded second in the Vp-PAI, VPA1334 (designated VocC; Vop chaperone C), appeared to be a T3SS chaperone candidate. The molecular weight and the isoelectric point of VocC were estimated as 14.3 kDa and 5.41, respectively. Based on the information from previously identified T3SS-associated chaperones (Feldman & Cornelis, 2003; Parsot et al., 2003), these values indicate that VocC is a possible T3SS2-associated chaperone for VopC, VopL, and VopT, and this result may categorize VocC as a type IB class chaperone, which chaperones multiple effectors (Parsot et al., 2003).