The cytosolic SycE and SycH chaperones of Yersinia protect the region of YopE and YopH involved in translocation across eukaryotic cell membranes

Abstract

Yersinia adhering at the surface of eukaryotic cells secrete a set of proteins called Yops. This secretion which occurs via a type III secretion pathway is immediately followed by the injection of some Yops into the cytosol of eukaryotic cells. Translocation of YopE and YopH across the eukaryotic cell membranes requires the presence of the translocators YopB and YopD. YopE and YopH are modular proteins composed of an N-terminal secretion signal, an internalization domain, and an effector domain. Secretion of YopE and YopH requires the presence of the specific cytosolic chaperones SycE and SycH, respectively. In this work, we have mapped the regions of YopE and YopH that are involved in binding of their cognate chaperone. There is only one Syc-binding domain in YopE (residues 15-50) and YopH (residues 20-70). This domain is localized immediately after the secretion signal and it corresponds to the internalization domain. Removal of this bifunctional domain did not affect secretion of YopE and YopH and even suppressed the need for the chaperone in the secretion process. Thus SycE and SycH are not secretion pilots. Instead, we propose that they prevent intrabacterial interaction of YopE and YopH with proteins involved in translocation of these Yops across eukaryotic cell membranes.

Protection Against Murine Listeriosis by Oral Vaccination with Recombinant Salmonella Expressing Hybrid Yersinia Type III Proteins

“…In contrast, no cytosolic delivery of these hybrid YopE proteins was observed in the absence of recombinant, plasmid-borne SycE. SycE is a small homodimeric protein that interacts with YopE in the Yersinia cytoplasm (53), and this interaction is absolutely required for YopE translocation (14), whereas YopE secretion is not affected. Obviously, SycE serves a similar essential purpose when expressed in Salmonella.…”

Protein secretion and the pathogenesis of bacterial infections

“…However, knockout mutations in sycE, encoding a small cytoplasmic protein that binds as a homodimer to YopE residues 15-100, abolish secretion of mutant YopE proteins (Cheng et al 1997;Lee et al 1998). Cytoplasmic binding proteins similar to SycE have been reported for YopB, YopD, YopH, YopN, and YopT (Wattiau and Cornelis 1993;Wattiau et al 1994;Woestyn et al 1996;Day and Plano 1998;Iriarte and Cornelis 1998;Jackson et al 1998). These results led to the proposal that YopE may be initiated into the type III pathway in one of two ways, requiring an mRNA signal or binding of SycE to unfolded YopE (Fig.…”

Docking of cytosolic chaperone-substrate complexes at the membrane ATPase during flagellar type III protein export

“…Export of these structural components is strongly facilitated by cytosolic substrate-specific chaperones, which bind respectively to the C-terminal amphipathic domains of their substrates FlgK and FlgL (chaperone FlgN), FliD (FliT), and FliC (FliS) (6)(7)(8). Although primary sequence identity is low or inapparent between the chaperones of the flagellar and virulence type III export systems, most are small, homodimeric proteins with a predicted C-terminal amphipathic helix (6,9,10), and it is suggested that they act as ''bodyguards'' to maintain monomers in an export-competent form and prevent their interaction before export (6,(10)(11)(12)(13). In the flagellar chaperones FlgN and FliT and the virulence chaperone CesT, the C-terminal region has been shown to mediate substrate binding, whereas the N terminus is responsible for homodimerization (7,14).…”