Affiliation:
1. Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College Dublin, Dublin 2, Ireland
Abstract
ABSTRACT
Here we report the characterization of an
Escherichia coli
gene (
agn43
) which encodes the principal phase-variable outer membrane protein termed antigen 43 (Ag43). The
agn43
gene encodes a precursor protein of 107 kDa containing a 52-amino-acid signal sequence. Posttranslational processing generates an α
43
subunit (predicted
M
r
of 49,789) and a C-terminal domain (β
43
) with features typical of a bacterial integral outer membrane protein (predicted
M
r
of 51,642). Secondary structure analysis predicts that β
43
exists as an 18-stranded β barrel and that Ag43 shows structural organization closely resembling that of immunoglobulin A1 protease type of exoprotein produced by pathogenic
Neisseria
and
Haemophilus
spp. The correct processing of the polyprotein to α
43
and β
43
in OmpT, OmpP, and DegP protease-deficient
E. coli
strains points to an autocatalytic cleavage mechanism, a hypothesis supported by the occurrence of an aspartyl protease active site within α
43
. Ag43, a species-specific antigen, possesses two RGD motifs of the type implicated in binding to human integrins. The mechanism of reversible phase variation was studied by immunochemical analysis of a panel of well-defined regulatory mutants and by analysis of DNA sequences upstream of
agn43
. Evidence strongly suggests that phase variation is regulated by both deoxyadenosine methylase (Dam) and by OxyR. Thus,
oxyR
mutants are locked on for Ag43 expression, whereas
dam
mutants are locked off for Ag43 expression. We propose a novel mechanism for the regulation of phase switching in which OxyR competes with Dam for unmethylated GATC sites in the regulatory region of the
agn43
gene.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
143 articles.
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