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J. Biol. Chem., Vol. 277, Issue 36, 32538-32545, September 6, 2002
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From the Department of Biochemistry, Duke University Medical
Center, Durham, North Carolina 27710
Heat-labile enterotoxin (LT) is an important
virulence factor expressed by enterotoxigenic Escherichia
coli. The route of LT secretion through the outer membrane
and the cellular and extracellular localization of secreted LT were
examined. Using a fluorescently labeled receptor, LT was found to be
specifically secreted onto the surface of wild type enterotoxigenic
Escherichia coli. The main terminal branch of the general
secretory pathway (GSP) was necessary and sufficient to localize LT to
the bacterial surface in a K-12 strain. LT is a heteromeric toxin, and
we determined that its cell surface localization was mediated by the
its B subunit independent of an intact GM1
ganglioside binding site and that LT binds lipopolysaccharide and
GM1 concurrently. The majority of LT secreted into the
culture supernatant by the GSP in E. coli associated with
vesicles. Only a mutation in hns, not overexpression of the
GSP or LT, caused an increase in vesicle yield, supporting a specific
vesicle formation machinery regulated by the nucleoid-associated protein HNS. We propose a model in which LT is secreted by the GSP across the outer membrane, secreted LT binds lipopolysaccharide via
a GM1-independent binding region on its B subunit, and LT on the surface of released outer membrane vesicles interacts with host
cell receptors, leading to intoxication. These data explain a novel
mechanism of vesicle-mediated receptor-dependent delivery of a
bacterial toxin into a host cell.
Bacterial Surface Association of Heat-labile Enterotoxin through
Lipopolysaccharide after Secretion via the General Secretory
Pathway*
*
This work was supported by a Burroughs Wellcome career award
(to M. J. K.) and an institutional research grant of the American Cancer Society.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: Dept. of Biochemistry,
Duke University Medical Center, Box 3711, Durham, NC 27710. Tel.:
919-684-2545; Fax: 919-684-8885; E-mail: meta.kuehn@duke.edu.
Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.
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