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J. Bacteriol., Apr 1995, 1719-1726, Vol 177, No. 7
I Fukuda, T Suzuki, H Munakata, N Hayashi, E Katayama, M Yoshikawa and C Sasakawa
The large plasmid-encoded outer membrane protein VirG (IcsA) of Shigella
flexneri is essential for bacterial spreading by eliciting polar deposition
of filamentous actin (F-actin) in the cytoplasm of epithelial cells. Recent
studies have indicated that VirG is located at one pole on the surface of
the bacterium and secreted into the culture supernatant and that in host
cells it is localized along the length of the F-actin tail. The roles of
these VirG phenotypes in bacterial spreading still remain to be elucidated.
In this study, we examined the surface-exposed portion of the VirG protein
by limited trypsin digestion of S. flexneri YSH6000 and determined the
sites for VirG processing during secretion into the culture supernatant.
Our results indicated that the 85-kDa amino-terminal portion of VirG is
located on the external side of the outer membrane, while the 37-kDa
carboxy- terminal portion is embedded in it. The VirG cleavage required for
release of the 85-kDa protein into the culture supernatant occurred at the
Arg-Arg bond at positions 758 to 759. VirG-specific cleavage was observed
in Shigella species and enteroinvasive Escherichia coli, which requires an
as yet unidentified protease activity governed by the virB gene on the
large plasmid. To investigate whether the VirG-specific cleavage occurring
in extracellular and intracellular bacteria is essential for VirG function
in bacterial spreading, the Arg-Arg cleavage site was modified to an
Arg-Asp or Asp-Asp bond.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Cleavage of Shigella surface protein VirG occurs at a specific site, but the secretion is not essential for intracellular spreading
Department of Bacteriology, University of Tokyo, Japan.
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