Extracellular Transport of VirG Protein in Shigella(*)
- From the Department of Bacteriology, Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo 108, Japan and the
- Laboratorie de Microbiologie et de Génétique, Université Louis-Pasteur, URA D-1481 CNRS, Institut de Botanique, 28, rue Goethe, 67083 Strasbourg, France
- § To whom correspondence should be addressed: Dept. of Bacteriology, Institute of Medical Science, University of Tokyo, 4-6-1, Shirokanedai, Minato-ku, Tokyo 108, Japan. Tel.: 81-3-5449-5252; Fax: 81-3-5449-5405.
Abstract
The ability of Shigella to spread within and between epithelial cells is a prerequisite for causing bacillary dysentery and requires the function encoded by the virG gene on the large plasmid. The outer membrane VirG (IcsA) protein 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 an N-terminal 80-kDa VirG portion is exposed on the bacterial cell surface and released into the external medium, while the following 37-kDa C-terminal portion is embedded in the outer membrane, although little is known about the extracellular transport of the VirG protein. In this study, we attempted to elucidate the export pathway of VirG protein across the outer membrane and found that the C-terminal 37-kDa portion, termed VirG β-core, serves as the self-transporter for the secretion of the preceding 80-kDa portion from the periplasmic side of the outer membrane to the external side. Indeed, foreign polypeptides such as MalE or PhoA covalently linked to the N terminus of VirG β-core were transported to the external side of the outer membrane, and it was further shown that the folding structure of the passenger polypeptide at the periplasmic side of the outer membrane interferes with its translocation. Analysis of the secondary structure of VirG β-core predicted that the critical structural property was a β-barrel channel consisting of amphipathic antiparallel transmembrane β-strands, interspersed by hairpin turns and loops. These results thus strongly suggest that the secretion of VirG protein from Shigella is similar to the export system utilized by the IgA protease of Neisseria.
Footnotes
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↵* This work was supported by Grant-in-aid for Scientific Research 07457070 from the Japanese Ministry of Education, Science, Sports and Culture. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵1 The abbreviations used are:
- bp
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base pair(s)
- 2-ME
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2-mercaptoethanol
- PAGE
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polyacrylamide gel electrophoresis
- PCR
-
polymerase chain reaction
- ELISA
-
enzyme-linked immunosorbent assay
- PBS
-
phosphate-buffered saline.
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↵2 T. Suzuki, unpublished results.
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- Received August 14, 1995.
- Revision received October 6, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
