What's the point of the type III secretion system needle?

Abstract

Recent work by several groups has significantly expanded our knowledge of the structure, regulation of assembly, and function of components of the extracellular portion of the type III secretion system (T3SS) of Gram-negative bacteria. This perspective presents a structure-informed analysis of functional data and discusses three nonmutually exclusive models of how a key aspect of T3SS biology, the sensing of host cells, may be performed.flagella ͉ structure

Structure of a type III secretion needle at 7-Å resolution provides insights into its assembly and signaling mechanisms

“…Although initially proposed to exist (2), no assembly cap has been found for the T3SS needle. However, given its small size, the needle protein may not need a polymerization-promoting complex (11). In view of the β-hairpin structure found, we now propose that the assembly process is as follows.…”

“…Point mutations in the needle protein lead to deregulated secretion as well as compositionally and functionally altered tips (5,9,10). Following discovery that short C-terminal deletions prevent MxiH polymerization, partial crystal and NMR structures from several species revealed a helix-turn-helix hairpin fold (11)(12)(13) (Fig. S1).…”

Atomic resolution structure of the cytoplasmic domain of Yersinia pestis YscU, a regulatory switch involved in type III secretion

“…1,2 Y. pestis and many other gram-negative bacterial pathogens use a type III secretion system (T3SS) as a protein transport apparatus to inject a small number of effector proteins through a hollow needle that extends across the inner and outer bacterial membranes and into the cytosol of eukaryotic cells. [3][4][5] The effector Yops (Yersinia outer proteins) enable the pathogenic bacteria to defeat the immune response of the host by interfering with the signal transduction pathways that regulate the actin cytoskeleton, phagocytosis, apoptosis, and the inflammatory response. 6 The export apparatus consists in part of cytoplasmic and inner-membrane proteins that identify T3SS substrates and control the switching of substrate specificity during morphogenesis and hostcell contact.…”

The Inside Story of Shigella Invasion of Intestinal Epithelial Cells

“…The Shigella Mxi-Spa T3SA is composed of 21 different proteins forming a basal body embedded in the bacterial inner and outer membranes prolonged by a needle capped by a socalled "tip complex" (Blocker et al 2008;Mueller et al 2008). As for flagella, the basal body consists of a series of rings formed by the oligomerization of different T3SA components.…”

“…The precise mechanism controlling the switch from nonactive to active secretion following tip contact is not known. The change of configuration of the tip complex proteins associated with interaction with a cell-surface receptor may lead to the emission of signals, involving MxiC and perhaps a tip-to-base transduction of signals through change of configuration of MxiH (Blocker et al 2008;Botteaux et al 2009;Fujii et al 2012). …”