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Journal of Bacteriology, May 1999, p. 3129-3135, Vol. 181, No. 10
Department of Biochemistry, American Red
Cross, Jerome H. Holland Laboratory, Rockville, Maryland
20855,1 and Department of
Microbiology, Michigan State University, East Lansing, Michigan
488242
Received 17 September 1998/Accepted 15 March 1999
The general secretion pathway of gram-negative bacteria is
responsible for extracellular secretion of a number of different proteins, including proteases and toxins. This pathway supports secretion of proteins across the cell envelope in two distinct steps,
in which the second step, involving translocation through the outer
membrane, is assisted by at least 13 different gene products. Two of
these components, the cytoplasmic membrane proteins EpsL and EpsM of
Vibrio cholerae, have been purified and characterized. Based on gel filtration analysis, both purified
EpsM(His)6 and wild-type EpsL present in an
Escherichia coli Triton X-100 extract are dimeric proteins.
EpsL and EpsM were also found to interact directly and form a Triton
X-100 stable complex that could be precipitated with either anti-EpsL
or anti-EpsM antibodies. In addition, when the L and M proteins were
coexpressed in E. coli, they formed a stable complex and
protected each other from proteolytic degradation, indicating that
these two proteins interact in vivo and that no other Eps protein is
required for their association. Since EpsL is predicted to contain a
large cytoplasmic domain, while EpsM is predominantly exposed on the
periplasmic side, we speculate that these components might be part of a
structure that is involved in bridging the inner and outer membranes.
Furthermore, since EpsL has previously been shown to interact with the
autophosphorylating cytoplasmic membrane protein EpsE, we hypothesize
that this trimolecular complex might be involved in regulating the
opening and closing of the secretion pore and/or transducing energy to
the site of outer membrane translocation.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Direct Interaction of the EpsL and EpsM Proteins of
the General Secretion Apparatus in Vibrio cholerae
*
Corresponding author. Mailing address: Department of
Biochemistry, American Red Cross, Jerome H. Holland Laboratory, 15601 Crabbs Branch Way, Rockville, MD 20855. Phone: (301) 738-0604. Fax:
(301) 738-0794. E-mail: sandkvis{at}usa.redcross.org.
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