Affiliation:
1. Department of Microbiology1 and
2. Molecular and Cellular Biology Program,2 Arizona State University, Tempe, Arizona 85287-2701, and
3. Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-32063
Abstract
ABSTRACT
A novel porin, OmpG, is produced in response to a chromosomal mutation termed
cog-192
. Molecular characterization of
cog-192
revealed that it is a large chromosomal deletion extending from the 3′ end of
pspA
through to the 5′ end of an open reading frame located immediately upstream of
ompG
. As a result of this 13.1-kb deletion, the expression of
ompG
was placed under the control of the
pspA
promoter. Characterization of OmpG revealed that it is quite different from other porins. Proteoliposome swelling assays showed that OmpG channels were much larger than those of the OmpF and OmpC porins, with an estimated limited diameter of about 2 nm. The channel lacked any obvious solute specificity. The folding model of OmpG suggests that it is the first 16-stranded β-barrel porin that lacks the large external loop, L3, which constricts the channels of other nonspecific and specific porins. Consistent with the folding model, circular dichroism showed that OmpG contains largely a β-sheet structure. In contrast to other
Escherichia coli
porins, there is no evidence that OmpG exists as stable oligomers. Although
ompG
DNA was present in all
E. coli
strains examined so far, its expression under laboratory conditions was seen only due to rare chromosomal mutations. Curiously, OmpG was constitutively expressed, albeit at low levels, in
Salmonella
,
Shigella
, and
Pseudomonas
species.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
86 articles.
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