Biology subjects

Sachar, K.

Publications and source records attributed to Sachar, K..

3 recordsLinked to original sources

bioRxiv2024

Structure of the type VI secretion system protein VgrS from Salmonella Typhimurium

Enteric bacterial pathogens employ various strategies to colonize the intestine and cause diseases ranging from gastroenteritis to systemic infections. For example, Salmonella enterica utilizes a nanomachine known as the type VI secretion system (T6SS) to facilitate colonization of the host gut. However, the varied mechanistic details of how the T6SS is loaded with effector proteins remains to be elucidated. Here, we present an X-ray crystal structure of the Salmonella Typhimurium VgrG (VgrS) that serves as platform for T6SS effector loading. Compared to other known structures of VgrG proteins, the VgrS trimer adopts an alternative open conformation composed of a domain-swap between the monomers in the gp27 region. Additionally, a comparative structural analysis of VgrS with other VgrG proteins reveals molecular variations that may contribute to specific effector loading mechanisms. Our structural data and molecular analysis highlight the observation that the T6SS of each bacterial species or strain is unique.

biochemistry↗

bioRxiv2021

Structure of a bacterial Rhs effector exported by the type VI secretion system

The type VI secretion system (T6SS) is a widespread protein export apparatus found in Gram-negative bacteria. The majority of T6SSs deliver toxic effector proteins into competitor bacteria. Yet, the structure, function, and activation of many of these effectors remains poorly understood. Here, we present the structures of the T6SS effector RhsA from Pseudomonas protegens and its cognate T6SS spike protein, VgrG1, at 3.3 [A] resolution. The structures reveal that the rearrangement hotspot (Rhs) repeats of RhsA assemble into a closed anticlockwise {beta}-barrel spiral similar to that found in bacterial insecticidal Tc toxins and in metazoan teneurin proteins. We find that the C-terminal toxin domain of RhsA is autoproteolytically cleaved but remains inside the Rhs cocoon where, with the exception of three ordered structural elements, most of the toxin is disordered. The N-terminal plug domain is unique to T6SS Rhs proteins and resembles a champagne cork that seals the Rhs cocoon at one end while also mediating interactions with VgrG1. Interestingly, this domain is also autoproteolytically cleaved inside the cocoon but remains associated with it. We propose that mechanical force is required to remove the cleaved part of the plug, resulting in the release of the toxin domain as it is delivered into a susceptible bacterial cell by the T6SS.

biochemistry↗

bioRxiv2020

Structural basis for effector transmembrane domain recognition by type VI secretion system chaperones

Type VI secretion systems facilitate the delivery of antibacterial effector proteins between neighbouring Gram-negative bacteria. A subset of these effectors harbor N-terminal transmembrane domains (TMDs) implicated in effector translocation across the target cell membrane. However, the abundance and distribution of these TMD-containing effectors has remained unknown. Here we report the discovery of prePAAR, a conserved motif found in over 6,000 putative TMD-containing effectors. Based on their differing sizes and number of TMDs these effectors fall into two distinct classes that are unified by their requirement for a member of the Eag family of T6SS chaperones for export. Co-crystal structures of class I and class II effector TMD-chaperone complexes from Salmonella Typhimurium and Pseudomonas aeruginosa, respectively, reveals that Eag chaperones mimic transmembrane helical packing to stabilize effector TMDs. In addition to participating in the chaperone-TMD interface, we find that prePAAR functions to facilitate proper folding of the downstream PAAR domain, which is required for effector interaction with the T6SS spike. Taken together, our findings define the mechanism of chaperone-assisted secretion of a widespread family of T6SS membrane protein effectors.

biochemistry↗