The Many Faces of IpaB.

Wendy L Picking,William D Picking

doi:10.3389/fcimb.2016.00012

Wendy L Picking, William D Picking

Open Access

https://doi.org/10.3389/fcimb.2016.00012

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Abstract

The type III secretion system (T3SS) is Shigella's most important virulence factor. The T3SS apparatus (T3SA) is comprised of an envelope-spanning basal body and an external needle topped by a tip complex protein called IpaD. This nanomachine is used to deliver effector proteins into host cells to promote pathogen entry. A key component of the matured T3SS needle tip complex is the translocator protein IpaB. IpaB can exist in multiple states when prepared as a recombinant protein, however, it has also been described as having additional roles in Shigella pathogenesis. This mini-review will briefly describe some of the features of IpaB as a T3SS needle tip protein, as a pore-forming translocator protein and as an effector protein. Reflection on the potential importance of the different in vitro states of IpaB on its function and importance in serotype-independent vaccines is also provided.

Highlights

IpaB from Shigella (Kubori et al, 1998; Mueller et al, 2005; Kawamoto et al, 2013; Hu et al, 2015).Among these, the T3SS apparatus (T3SA) of Shigella and that encoded by the Salmonella Pathogenicity Island 1 (SPI-1) are the most closely related with respect to overall structure and the structure of the controlling needle tip complex that is described below
Much of what is known of the T3SA structure stems from transmission electron microscopy studies of S. flexneri and Salmonella Typhimurium (Kubori et al, 1998; Blocker et al, 1999; Tamano et al, 2000; Sani et al, 2007; Veenendaal et al, 2007; Lara-Tejero et al, 2011)
Further high-resolution structural information will be needed for purified recombinant IpaB and in situ (TC-localized) IpaB before this will be known with certainty

Summary

INTRODUCTION

Shigella species (S. flexneri, S. dysenteriae, S. sonnei, and S. boydii) are etiologic agents of shigellosis, a potentially life-threatening bacillary dysentery. Infection is initiated when Shigella crosses M cells and invades/kills resident macrophages in the associated lymphoid tissues (Zychlinsky et al, 1992). This provides the bacterium with access to the basal side of the colonic epithelium. The T3SS apparatus (T3SA) is a complex nanomachine used to deliver bacterial effector proteins directly into and across eukaryotic cell membranes. The effector proteins that are responsible for subverting host cell activities are pathogen specific with regard to their functions and roles in pathogenesis (Bulgin et al, 2010; Plano and Schesser, 2013; Raymond et al, 2013). IpaB from Shigella (Kubori et al, 1998; Mueller et al, 2005; Kawamoto et al, 2013; Hu et al, 2015).Among these, the T3SA of Shigella and that encoded by the Salmonella Pathogenicity Island 1 (SPI-1) are the most closely related with respect to overall structure and the structure of the controlling needle tip complex that is described below

A Brief Overview of the Shigella T3SA

CONCLUDING REMARKS