title: Residues of heat-labile enterotoxin involved in bacterial cell surface binding.
abstract: Enterotoxigenic Escherichia coli (ETEC) is a leading cause of traveler's diarrhea worldwide. One major virulence factor released by this pathogen is the heat-labile enterotoxin LT, which upsets the balance of electrolytes in the intestine. After export, LT binds to lipopolysaccharide (LPS) on the bacterial surface. Although the residues responsible for LT's binding to its host receptor are known, the portion of the toxin which mediates LPS binding has not been defined previously. Here, we describe mutations in LT that impair the binding of the toxin to the external surface of E. coli without altering holotoxin assembly. One mutation in particular, T47A, nearly abrogates surface binding without adversely affecting expression or secretion in ETEC. Interestingly, T47A is able to bind mutant E. coli expressing highly truncated forms of LPS, indicating that LT binding to wild-type LPS may be due primarily to association with an outer core sugar. Consequently, we have identified a region of LT distinct from the pocket involved in eukaryotic receptor binding that is responsible for binding to the surface of E. coli.
authors.affiliation: Department of Molecular Genetics, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Mudrak
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Rodriguez
authors.forename: Meta J
authors.initials: MJ
authors.lastname: Kuehn
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D054307:Enterotoxigenic Escherichia coli / Q000502:physiology*; D004768:Enterotoxins / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism; D020125:Mutation, Missense; D011485:Protein Binding
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D008070:Lipopolysaccharides; C027538:heat-labile enterotoxin, E coli