The chaperone‐like protein YerA of Yersinia pseudotuberculosis stabilizes YopE in the cytoplasm but is dispensible for targeting to the secretion loci

Abstract

The virulence plasmid-encoded YopE cytotoxin of Yersinia pseudotuberculosis is secreted across the bacterial membranes and subsequently translocated into the eukaryotic cell. Translocation of YopE into target cells was recently shown to be polarized and only occurred at the zone of contact between the pathogen and the eukaryotic cell. Immunogold electron microscopy on cryosectioned Y. pseudotuberculosis revealed that YopE is secreted and deposited on the bacterial cell surface when the bacteria are grown in Ca(2+)-depleted media at 37 degrees C. No YopE was detected in the cytoplasm or in the membranes. In yerA mutants which are downregulated for YopE at a post-transcriptional level, the cytotoxin could only be detected in the cytoplasm. The overall recovery of YopE from the yerA mutant strain was, however, considerably lower than from the wild-type strain. yerA had no major effect on the translation of YopE, but was found to stabilize YopE in the cytoplasm. YerA was shown to specifically interact with YopE in the cytoplasm in vivo and this binding also correlated with YopE secretion. Targeting of YopE to the secretion loci as well as translocation of YopE into HeLa cells occurred also in the absence of YerA. Based on our findings, we suggest that YerA by binding to YopE stabilizes and maintains the cytotoxin in a secretion-competent conformation.

Intracellular targeting of exoenzyme S of Pseudomonas aeruginosa via type III‐dependent translocation induces phagocytosis resistance, cytotoxicity and disruption of actin microfilaments

“…The infection and fractionation of HeLa cells has been described previously (Frithz-Lindsten et al, 1995). In this study, the protocol was slightly modified.…”

Functional conservation of the secretion and translocation machinery for virulence proteins of yersiniae, salmonellae and shigellae.

“…The detailed function of the Syc chaperones has not yet been determined, but two alternative models have been suggested; either the chaperone acts as a pilot protein and targets the Yop to the secretion organelle or the chaperone binds to the Yop to retain the protein in a secretion-competent form (Wattiau et al, 1993Frithz-Lindsten et al, 1995 (Menard et al, 1994). IpgC stabilizes IpaB in the bacterial cytoplasm and ipgC mutants show lower levels of IpaB in the culture supernatant (Menard et al, 1994).…”

“…YopE and YopH are both dependent on specific cytoplasmic chaperones, YerA (SycE) and SycH respectively, for secretion and each Yop protein has been suggested to have its own chaperone (Wattiau and Cornelis, 1993;Wattiau et al, 1994;Frithz-Lindsten et al, 1995;Persson et al, in preparation). The detailed function of the Syc chaperones has not yet been determined, but two alternative models have been suggested; either the chaperone acts as a pilot protein and targets the Yop to the secretion organelle or the chaperone binds to the Yop to retain the protein in a secretion-competent form (Wattiau et al, 1993Frithz-Lindsten et al, 1995 (Menard et al, 1994).…”

Molecular and cell biology aspects of plague

“…This observation indicates that the binding site itself creates the need for the chaperone and suggests that the chaperone acts as a ''bodyguard'' protecting this site from premature associations that would lead to degradation. In agreement with this first hypothesis, SycE has been shown to protect YopE from intrabacterial degradation: the half-life of YopE is longer in wild-type bacteria than in sycE mutant bacteria (37,38). The partners in these hypothetical premature associations could be the translocators (36), but such interactions could not be demonstrated.…”