Identification of divergent type VI secretion effectors using a conserved chaperone domain

Abstract

The type VI secretion system (T6SS) is a lethal weapon used by many bacteria to kill eukaryotic predators or prokaryotic competitors. Killing by the T6SS results from repetitive delivery of toxic effectors. Despite their importance in dictating bacterial fitness, systematic prediction of T6SS effectors remains challenging due to high effector diversity and the absence of a conserved signature sequence. Here, we report a class of T6SS effector chaperone (TEC) proteins that are required for effector delivery through binding to VgrG and effector proteins. The TEC proteins share a highly conserved domain (DUF4123) and are genetically encoded upstream of their cognate effector genes. Using the conserved TEC domain sequence, we identified a large family of TEC genes coupled to putative T6SS effectors in Gram-negative bacteria. We validated this approach by verifying a predicted effector TseC in Aeromonas hydrophila. We show that TseC is a T6SS-secreted antibacterial effector and that the downstream gene tsiC encodes the cognate immunity protein. Further, we demonstrate that TseC secretion requires its cognate TEC protein and an associated VgrG protein.Distinct from previous effector-dependent bioinformatic analyses, our approach using the conserved TEC domain will facilitate the discovery and functional characterization of new T6SS effectors in Gram-negative bacteria.interspecies interaction | colicin | antitoxin | toxin | protein secretion

VgrG C terminus confers the type VI effector transport specificity and is required for binding with PAAR and adaptor–effector complex

“…5A), we hypothesized that in addition to VgrG1, Atu4349 and Atu4352 may play roles in Tde1 translocation. This hypothesis was indeed supported by our previous observation that the DUF4123-domain-containing protein Atu4349 interacts directly with Tde1 to form a complex in E. coli and stabilizes Tde1 in A. tumefaciens C58 (6), and two recent studies identifying a V. cholerae DUF4123-domain-containing protein, Tap-1/Tec, required for loading a specific effector onto cognate VgrG for secretion (32,33). Thus, we first determined the role of atu4349 (named tap-1) and atu4352 (named paar) in Tde1 secretion and Tde1-dependent antibacterial activity.…”

“…One is PAAR protein, which interacts directly with the last β-strand of a gp5-VgrG chimera and can act as an adaptor between VgrG and effector to facilitate secretion of a broad range of T6SS toxins (28). Others include the DUF4123-domain-containing protein Tap-1/Tec for loading a specific effector onto cognate VgrG for delivery in V. cholerae (32,33) and EagR accessory protein specifically required for deployment of its associated Rhs effector in Serratia marcescens (8). We found that all tde1 orthologs are linked to an upstream tap-1, and except for in I. limosus, are associated with a downstream paar gene (Fig.…”

“…(30,31). Recent studies further identified a DUF4123-domaincontaining protein, Tap-1/Tec, that is required for loading a specific effector onto cognate VgrG for delivery in V. cholerae (32,33). Interestingly, the C terminus of VgrG in Escherichia coli Sci-1 T6SS interacts directly with the Tle1 phospholipase effector for delivery without bridging by an adaptor protein (11).…”

“…For vgrG1-type gene clusters, a gene encoding for a protein with the DUF4123 domain known as an adaptor/chaperone (6,32,33) is always found between vgrG1 and tde1 (Fig. 5A).…”

Microbial Herd Protection Mediated by Antagonistic Interaction in Polymicrobial Communities

“…We previously characterized the T6SS antibacterial activities of two waterborne pathogens, Vibrio cholerae strain V52 (13) and Aeromonas hydrophila strain SSU (21). V. cholerae possesses four antimicrobial effectors, namely, VgrG3, which functions as a lysozyme (13,22); the lipase TseL (13,23); VasX, which has a colicin-like domain (13,24); and the hydrolase TseH (25), which seems to play only a minor role in interbacterial killing (25).…”