Structural basis for the pathogenesis of Campylobacter jejuni Hcp1, a structural and effector protein of the Type VI Secretion System

Abstract

The Type VI Secretion System (T6SS) provides enhanced virulence to Campylobacter jejuni and has been associated with a high incidence of bloody diarrhea. The hemolysin-coregulated protein (Hcp)-the hallmark of the T6SS-can act as a structural and effector protein. Unlike other T6SS-harboring bacteria, which possess multiple Hcp proteins each performing different functions, C. jejuni possesses only one Hcp protein, and its structural and functional role has not been elucidated previously. Here, we report the structure and functional studies of Hcp from C. jejuni. We found similarities between the hexameric ring structure of Hcp-Cj and that of Hcp3 from Pseudomonas aeruginosa. Through functional studies, we showed two roles for Hcp-Cj that is, in cytotoxicity toward HepG2 cells and in biofilm formation in C. jejuni. In structure-based mutational analyses, we showed that an Arg-to-Ala mutation at position 30 within the extended loop results in a significant decrease in cytotoxicity, suggesting a role for this loop in binding to the host cell. However, this mutation does not affect its biofilm formation function. Collectively, this study supports the dual role of Hcp-Cj as a structural and effector protein in C. jejuni.

Bioinformatic Analysis of the Campylobacter jejuni Type VI Secretion System and Effector Prediction

“…In C. jejuni, the T6SS biological functions have been associated with host colonisation, cell adhesion and invasion, survival in bile salts, contact-dependent lysis of erythrocytes, and contributing to oxidative stress (Lertpiriyapong et al, 2012;Bleumink-Pluym et al, 2013;Liaw et al, 2019). So far, Hcp has been suggested as a T6SS effector contributing to C. jejuni host cell adhesion and invasion (Lertpiriyapong et al, 2012;Bleumink-Pluym et al, 2013;Noreen et al, 2018); however, no evidence currently supports the direct contribution to these phenotypes by Hcp in isolation. Whilst few studies have indicated the prevalence of T6SS in C. jejuni (Harrison et al, 2014;Corcionivoschi et al, 2015;Ugarte-Ruiz et al, 2015), a larger comprehensive bioinformatic analysis of T6SS within C. jejuni and the identification of associated effectors are still needed.…”

Analysis of complete Campylobacter concisus genomes identifies genomospecies features, secretion systems and novel plasmids and their association with severe ulcerative colitis

“…Hcp is a structural protein of the T6SS and is also secreted by the T6SS. Secreted Hcp has been used as a hallmark to indicate functional T6SS [55][56][57][58]. Campylobacter jejuni also has a functional T6SS without ClpV, suggesting that it may be common for Campylobacter species to use alternative ATPase instead of ClpV in performing T6SS function [55].…”

The Campylobacter jejuni Type VI Secretion System Enhances the Oxidative Stress Response and Host Colonization

“…Previous studies have demonstrated the C. jejuni T6SS may be important in host cell adherence and invasion, colonization, survival in bile salts and contact-dependent cytotoxicity toward red blood cells (Lertpiriyapong et al, 2012;Bleumink-Pluym et al, 2013). A recent study examined the structure of the TssD effector in C. jejuni and found that TssD is cytotoxic toward HepG2 human liver carcinoma cells (Noreen et al, 2018). However, whether the T6SS plays a role in the survival and infection of C. jejuni in poultry, a primary reservoir in humans is still unknown.…”