title: A single amino acid substitution in B subunit of Escherichia coli enterotoxin affects its oligomer formation.
abstract: We isolated a mutant strain of enterotoxigenic Escherichia coli by nitrosoguanidine mutagenesis, which produces an immunologically altered B subunit of heat-labile enterotoxin. This mutant B subunit was detected as a monomer on sodium dodecyl sulfate-polyacrylamide gel electrophoresis even without prior heating, suggesting a problem in oligomer formation. Furthermore, this mutant B subunit could not form holotoxin with the native A subunit, and the affinity to GM1-ganglioside receptor was 10-fold lower than that of the native B subunit. The amino acid sequence analysis of this mutant B subunit revealed only one amino acid substitution compared with the native B subunit, at the 64th position from the N terminus (valine instead of alanine). These data suggest that the alanine at position 64 from the N terminus is important for the native B subunit to form an oligomer structure and express its functions.
authors.affiliation: Department of Bacteriology and Serology, Osaka University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Iida
authors.forename: T
authors.initials: T
authors.lastname: Tsuji
authors.forename: T
authors.initials: T
authors.lastname: Honda
authors.forename: T
authors.initials: T
authors.lastname: Miwatani
authors.forename: S
authors.initials: S
authors.lastname: Wakabayashi
authors.forename: K
authors.initials: K
authors.lastname: Wada
authors.forename: H
authors.initials: H
authors.lastname: Matsubara
mesh_terms: D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D001427:Bacterial Toxins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004768:Enterotoxins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D005677:G(M1) Ganglioside / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000032:analysis; D011994:Recombinant Proteins / Q000096:biosynthesis; D014633:Valine / Q000235:genetics
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D011994:Recombinant Proteins; C034993:ganglioside receptor; D005677:G(M1) Ganglioside; C027538:heat-labile enterotoxin, E coli; D014633:Valine; D000409:Alanine