Characterization of a Type III secretion substrate specificity switch (T3S4) domain in YscP from Yersinia enterocolitica

Abstract

SummaryThe length of the needle ending the Yersinia Ysc injectisome is determined by YscP, a protein acting as a molecular ruler. In addition, YscP is required for Yop secretion. In the present paper, by a systematic deletion analysis, we localized accurately the region required for Yop secretion between residues 405 and 500. As this C-terminal region of YscP has also been shown to control needle length it probably represents the substrate specificity switch of the machinery. By a bioinformatics analysis, we show that this region has a globular structure, an original a a a a / b b b b fold, a P-x-L-G signature and presumably no catalytic activity. In spite of very limited sequence similarities, this structure is conserved among the proteins that are presumed to control the needle length in many different injectisomes and also among members of the FliK family, which control the flagellar hook length. This region thus represents a new protein domain that we called T3S4 for Type III secretion substrate specificity switch. The T3S4 domain of YscP can be replaced by the T3S4 domain of AscP ( Aeromonas salmonicida ) or PscP ( Pseudomonas aeruginosa ) but not by the one from FliK, indicating that in spite of a common global structure, these domains need to fit their partner proteins in the secretion apparatus.

Identification ofPseudomonas syringaepv. syringae 61 Type III Secretion System Hrp Proteins That Can Travel the Type III Pathway and Contribute to the Translocation of Effector Proteins into Plant Cells

“…HrpP has a C-terminal T3S4 like that of the Yersinia YscP, but HrpP and its homologs in other plant pathogens are much smaller (1). This observation suggests that HrpP has a role in substrate switching but is not a molecular ruler controlling pilus length in P. syringae.…”

“…The Yersinia YscP protein functions as a molecular ruler that determines the length of the YscF needle (31). The YscP protein also has a type III secretion substrate specificity switch domain (T3S4), which acts in concert with YscU to switch pathway traffic from channel components to effectors (1). The length of YscP controls the length of the needle so that the needle can extend beyond bacterial surface structures (notably the YadA adhesin), thus enabling needle contact with the host cell cytoplasmic membrane (39).…”

Rejection of Impassable Substrates by Yersinia Type III Secretion Machines

“…However, as bacteria encounter immune cells during infection, type III secretion becomes essential in preventing phagocytic killing of the invading microbes (50,65,66). The expression of genes encoding type III machines and their substrates is regulated in all bacterial species, and there is increasing evidence not only that each microbial species employs unique sets of genes encoding type III effector proteins for host cell injection but also that the order in which these polypeptides are transported is developmentally determined (1,32,39,59).…”

Functional Characterization of the Type III Secretion Substrate Specificity Switch Protein HpaC from Xanthomonas campestris pv. vesicatoria

“…To date, the molecular mechanisms underlying the T3S substrate specificity switch have been studied intensively in animal-pathogenic bacteria. It has been shown that the switch depends on secreted regulatory proteins, designated T3S substrate specificity switch (T3S4) proteins and including, e.g., YscP from Yersinia spp., Spa32 from Shigella flexneri, and FliK from the flagellar T3S system (1,35,50,53,66). T3S4 proteins share limited amino acid sequence similarity with each other but contain a structurally conserved C-terminal domain, termed the T3S4 domain, which is presumably crucial for protein function (1,9,52,56).…”

“…It has been shown that the switch depends on secreted regulatory proteins, designated T3S substrate specificity switch (T3S4) proteins and including, e.g., YscP from Yersinia spp., Spa32 from Shigella flexneri, and FliK from the flagellar T3S system (1,35,50,53,66). T3S4 proteins share limited amino acid sequence similarity with each other but contain a structurally conserved C-terminal domain, termed the T3S4 domain, which is presumably crucial for protein function (1,9,52,56). Experimental evidence reported for Spa32 and FliK suggests that T3S4 proteins interact with the C-terminal cytoplasmic domains of members of the conserved FlhB/YscU family of inner membrane proteins, which are proposed to be involved in the recognition of T3S substrates (9,54,55).…”