Affiliation:
1. Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66045-2106
Abstract
ABSTRACT
Enterotoxigenic
Escherichia coli
(ETEC) strain H10407 is capable of invading epithelial cell lines derived from the human ileocecum and colon in vitro. Two separate chromosomally encoded invasion loci (
tia
and
tib
) have been cloned from this strain. These loci direct nonadherent and noninvasive laboratory strains of
E. coli
to adhere to and invade cultured human intestinal epithelial cells. The
tib
locus directs the synthesis of TibA, a 104-kDa outer membrane protein that is directly correlated with the adherence and invasion phenotypes. TibA is synthesized as a 100-kDa precursor (preTibA) that must be modified for biological activity. Outer membranes of recombinant
E. coli
expressing TibA or preTibA were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and blotted to nitrocellulose. The presence of glycoproteins was detected by oxidization of carbohydrates with periodate and labeling with hydrazide-conjugated digoxigenin. Only TibA could be detected as a glycoprotein. Complementation experiments with
tib
deletion mutants of ETEC strain H10407 demonstrate that the TibA glycoprotein is expressed in H10407, that the entire
tib
locus is required for TibA synthesis, and that TibA is the only glycoprotein produced by H10407. Protease treatment of intact H10407 cells removes the carbohydrates on TibA, suggesting that they are surface exposed. TibA shows homology with AIDA-I from diffuse-adhering
E. coli
and with pertactin precursor from
Bordetella pertussis
. Both pertactin and AIDA-I are members of the autotransporter family of outer membrane proteins and are afimbrial adhesins that play an important role in the virulence of these organisms. Analysis of the predicted TibA amino acid sequence indicates that TibA is also an autotransporter. Analysis of the
tib
locus DNA sequence revealed an open reading frame with similarity to RfaQ, a glycosyltransferase. The product of this
tib
locus open reading frame is proposed to be responsible for TibA modification. These results suggest that TibA glycoprotein acts as an adhesin that may participate in the disease process.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
147 articles.
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