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Journal of Bacteriology, February 2000, p. 742-748, Vol. 182, No. 3
Department of Biochemistry, American Red
Cross, Holland Laboratory, Rockville, Maryland
208551; Vaccine and Therapeutic
Development Section, Oral Infection and Immunity Branch, National
Institute of Dental Research, National Institutes of Health, Bethesda,
Maryland 20892-43502; Department of
Microbiology, Michigan State University, East Lansing, Michigan
488243; and Department of Biology,
University of Regina, Regina, Saskatchewan, Canada S4S
0A24
Received 24 August 1999/Accepted 8 November 1999
Extracellular secretion of proteins via the type II or general
secretion pathway in gram-negative bacteria requires the assistance of
at least 12 gene products that are thought to form a complex apparatus
through which secreted proteins are translocated. Although this
apparatus is specifically required only for the outer membrane translocation step during transport across the bacterial cell envelope,
it is believed to span both membranes. The EpsE, EpsL, and EpsM
proteins of the type II apparatus in Vibrio cholerae are
thought to form a trimolecular complex that is required to either
control the opening and closing of the secretion pore or to transduce
energy to the site of outer membrane translocation. EpsL is likely to
play an important role in this relay by interacting with both the
cytoplasmic EpsE protein and the cytoplasmic membrane protein EpsM,
which is predominantly exposed on the periplasmic side of the membrane.
We have now extended this model and mapped the separate regions within
EpsL that contain the EpsE and EpsM binding domains. By taking
advantage of the species specificity of the type II pathway, we have
used chimeric proteins composed of EpsL and its homologue, ExeL, from
Aeromonas hydrophila together with either EpsE or its
Aeromonas homologue, ExeE, to complement the secretion
defect in both epsL and exeL mutant strains.
These studies have mapped the species-specific EpsE binding site to the
N-terminal cytoplasmic region between residues 57 and 216 of EpsL. In
addition, the species-specific EpsM binding site was mapped to the
C-terminal half of EpsL by coimmunoprecipitation of EpsM with different
EpsL-ExeL chimeras. This site is present in the region between amino
acids 216 and 296, which contains the predicted membrane-spanning
segment of EpsL.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Two Regions of EpsL Involved in Species-Specific Protein-Protein
Interactions with EpsE and EpsM of the General Secretion Pathway in
Vibrio cholerae
*
Corresponding author. Mailing address: Department of
Biochemistry, American Red Cross, 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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