title: Molecular evolution and mosaic structure of alpha, beta, and gamma intimins of pathogenic Escherichia coli.
abstract: Two types of pathogenic Escherichia coli, enteropathogenic E. coli (EPEC) and enterohemorrhagic E. coli (EHEC), cause diarrheal disease by disrupting the intestinal environment through the intimate attachment of the bacteria to the intestinal epithelium. This process is mediated by intimin, an outer membrane protein that is homologous to the invasins of pathogenic Yersinia. The intimin (eae) gene is part of a pathogenicity island, a 35-kb segment of DNA that has been acquired independently in different groups of pathogens. Nucleotide sequences of eae of three EPEC and four EHEC strains representing distinct clonal lineages revealed an exceptionally high level of divergence (15%) in the amino acid sequences of alpha, beta, and gamma intimin molecules, most of which is concentrated in the C-terminal region. The gamma intimin sequences from E. coli strains with serotypes O157:H7, O55:H7, and O157:H- are virtually identical, supporting the hypothesis that these bacteria belong to a single clonal lineage. Sequences of beta intimin of EPEC strains of serotypes O111:H2 and O128:H2 show substantial differences from alpha and gamma intimins, indicating that these strains have evolved independently. Strong nonrandom clustering of polymorphic sites indicates that the intimin genes are mosaics, suggesting that protein divergence has been accelerated by recombination and diversifying selection.
authors.affiliation: Institute of Molecular Evolutionary Genetics, Pennsylvania State University, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: McGraw
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: R K
authors.initials: RK
authors.lastname: Selander
authors.forename: T S
authors.initials: TS
authors.lastname: Whittam
mesh_terms: D018829:Adhesins, Bacterial; D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins; D017931:DNA Primers / Q000235:genetics; D004926:Escherichia coli / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*; D019453:Escherichia coli O157 / Q000235:genetics / Q000472:pathogenicity; D029968:Escherichia coli Proteins; D019143:Evolution, Molecular; D006801:Humans; D008969:Molecular Sequence Data; D009030:Mosaicism; D011995:Recombination, Genetic; D017386:Sequence Homology, Amino Acid; D012703:Serotyping
chemical_list: D018829:Adhesins, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; C053476:invasin, Yersinia; C073819:eaeA protein, E coli