Journal of Bacteriology, July 2000, p. 4077-4086, Vol. 182, No. 14
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Departments of Microbiology,1 Medicine,3 and Medicinal Chemistry,2 University of Washington, Seattle, Washington 98195
Received 7 March 2000/Accepted 2 May 2000
The outer membrane protein contents of Salmonella
enterica serovar Typhimurium strains with PhoP/PhoQ regulon
mutations were compared by two-dimensional gel electrophoresis. At
least 26 species of outer membrane proteins (OMPs) were identified as
being regulated by PhoP/PhoQ activation. One PhoP/PhoQ-activated OMP
was identified by semiautomated tandem mass spectrometry coupled with
electronic database searching as PgtE, a member of the
Escherichia coli OmpT and Yersinia pestis Pla
family of outer membrane proteases. Salmonella PgtE
expression promoted resistance to alpha-helical cationic antimicrobial
peptides (
-CAMPs). Strains expressing PgtE cleaved C18G, an
18-residue
-CAMP present in culture medium, indicating that protease
activity is likely to be the mechanism of OmpT-mediated resistance to
-CAMPs. PhoP/PhoQ did not regulate the transcription or export of
PgtE, indicating that another PhoP/PhoQ-dependent mechanism is required
for PgtE outer membrane localization. PgtE is a posttranscriptionally
regulated component of the PhoP/PhoQ regulon that contributes to
Salmonella resistance to innate immunity.
Present address: Bruker Daltonics, Billerica, MA 01821.
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