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Journal of Bacteriology, September 1998, p. 4452-4459, Vol. 180, No. 17
Department of
Microbiology1 and
Molecular and Cellular
Biology Program,2 Arizona State University,
Tempe, Arizona 85287-2701, and
Department of Molecular and Cell
Biology, University of California, Berkeley, California
94720-32063
Received 10 April 1998/Accepted 26 June 1998
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
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Biochemistry and Regulation of a Novel
Escherichia coli K-12 Porin Protein, OmpG, Which
Produces Unusually Large Channels
-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
-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.
*
Corresponding author. Mailing address: Department of
Microbiology, Arizona State University, Tempe, AZ 85287-2701. Phone: (602) 965-3320. Fax: (602) 965-0098. E-mail:
rajeev.misra{at}asu.edu.
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