A conserved domain in type III secretion links the cytoplasmic domain of InvA to elements of the basal body.

Mirjana Lilic,Cindy M Quezada,C Erec Stebbins

doi:10.1107/s0907444910010796

Mirjana Lilic, Cindy M Quezada + Show 1 more

Open Access

https://doi.org/10.1107/s0907444910010796

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Abstract

Protein type III secretion systems (T3SSs) are organic nanosyringes that achieve an energy-dependent translocation of bacterial proteins through the two membranes of Gram-negative organisms. Examples include the pathogenic systems of animals, plants and symbiotic bacteria that inject factors into eukaryotic cells, and the flagellar export system that secretes flagellin. T3SSs possess a core of several membrane-associated proteins that are conserved across all known bacterial species that use this system. The Salmonella protein InvA is one of the most highly conserved proteins of this core of critical T3SS components. The crystal structure of a C-terminal domain of InvA reveals an unexpected homology to domains that have been repeatedly found as building blocks of other elements of the T3SS apparatus. This suggests the surprising hypothesis that evolution has produced a significant component of the apparatus structure through a series of gene-duplication and gene-rearrangement events.

Highlights

A number of Gram-negative bacterial pathogens, including those causing disease in animals as well as in plants, utilize a highly specialized nanomachine termed the type III secretion system (T3SS) to achieve a remarkable translocation of bacterial proteins across three membranes and directly into the cytoplasm of the host organism (Galan & Wolf-Watz, 2006; Cornelis, 2006)
Conserved across pathogenic bacteria, as well as with a conserved homolog in the flagellar system (FlhA), InvA is critical to the functioning of the T3SS (Galan et al, 1992; Ginocchio & Galan, 1995)
Cells were harvested by centrifugation and the pellet was dissolved in a buffer consisting of 25 mM Tris–HCl pH 8.0, 200 mM NaCl, 5 mM imidazole pH 8.0, 1 mM phenylmethanesulfonyl fluoride (PMSF) and lysed using an Emulsiflex C-5 cell homogenizer (Avestin Inc., Ottawa, Ontario, Canada)

Summary

Introduction

A number of Gram-negative bacterial pathogens, including those causing disease in animals as well as in plants, utilize a highly specialized nanomachine termed the type III secretion system (T3SS) to achieve a remarkable translocation of bacterial proteins across three membranes and directly into the cytoplasm of the host organism (Galan & Wolf-Watz, 2006; Cornelis, 2006). These virulence proteins, often called ‘effectors’, hijack eukaryotic biochemical processes in sophisticated ways for the benefit of the pathogen (Cunnac et al, 2009; Parsot, 2009; McGhie et al, 2009; Poueymiro & Genin, 2009; Galan, 2009). Apart from its sequence similarity to analogous components of other T3SSs, InvA shows no primary sequence similarity to any proteins of known function

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