Role of the Pilot Protein YscW in the Biogenesis of the YscC Secretin in Yersinia enterocolitica

Abstract

The YscC secretin is a major component of the type III protein secretion system of Yersinia enterocolitica and forms an oligomeric structure in the outer membrane. In a mutant lacking the outer membrane lipoprotein YscW, secretion is strongly reduced, and it has been proposed that YscW plays a role in the biogenesis of the secretin. To study the interaction between the secretin and this putative pilot protein, YscC and YscW were produced in trans in a Y. enterocolitica strain lacking all other components of the secretion machinery. YscW expression increased the yield of oligomeric YscC and was required for its outer membrane localization, confirming the function of YscW as a pilot protein. Whereas the pilot-binding site of other members of the secretin family has been identified in the C terminus, a truncated YscC derivative lacking the C-terminal 96 amino acid residues was functional and stabilized by YscW. Pulse-chase experiments revealed that ϳ30 min were required before YscC oligomerization was completed. In the absence of YscW, oligomerization was delayed and the yield of YscC oligomers was strongly reduced. An unlipidated form of the YscW protein was not functional, although it still interacted with the secretin and caused mislocalization of YscC even in the presence of wild-type YscW. Hence, YscW interacts with the unassembled YscC protein and facilitates efficient oligomerization, likely at the outer membrane.

HxcQ Liposecretin Is Self-piloted to the Outer Membrane by Its N-terminal Lipid Anchor

“…The IM localization of secretin multimers in the absence of a functional pilotin has already been reported for the PulD and YscC secretins, respectively involved in type II and type III secretion (41,8).…”

“…This OM component belongs to a family of proteins generically designated as secretins (6). This family also includes members that are involved in type III protein secretion (T3SS), type IV pilus assembly, type IV bundle-forming pili, toxin co-regulated pili, and assembly and export of filamentous phage (7)(8)(9)(10)(11)(12). Therefore, secretins constitute an important group of transporters specialized in the translocation of bulky macromolecules or macromolecular complexes across the OM.…”

“…In most cases, pilot proteins are outer membrane-linked lipoproteins called pilotins. To date, characterized secretin/pilotin couples are: PulD/PulS of Klebsiella (17)(18), OutD/OutS of Erwinia (19) for T2SS; YscC/ YscW of Yersinia (8), InvG/InvH of Salmonella (12), MxiD/ MxiM of Shigella (20) for T3SS, and PilQ/Tgl of Myxococcus (21) for Type IV pilus systems. For T2SS secretin/pilotin couples, the specific pilotin binding domain is localized at the extreme C terminus of the secretin (19,22).…”

Membrane localization and topology of the Yersinia pestis YscJ lipoprotein

“…YscC and InvG are members of the secretin family and have been shown to form ring-shaped structures in the bacterial outer membrane (OM) (Crago & Koronakis, 1998;Koster et al, 1997). Stable expression, OM localization and oligomerization of YscC requires a lipoprotein chaperone, termed YscW, and the insertion of two DsbA-dependent disulfide bonds in the C-terminal region of the protein (Burghout et al, 2004;Jackson & Plano, 1999;Koster et al, 1997).…”

The type III secretion injectisome, a complex nanomachine for intracellular ‘toxin’ delivery

“…They have a conserved Cterminal membrane spanning domain, predicted to be a b-barrel, and a variable N-terminal domain extending in the periplasm. The proper insertion of secretins in the OM requires the assistance of a lipoprotein (YscW family) anchored in the OM (Crago and Koronakis, 1998;Daefler and Russel, 1998;Burghout et al, 2004a). The crystal structure of the N-terminal domain of EscC, the homolog of YscC in EPECs was recently solved (Spreter et al, 2009).…”