A single amino acid substitution in B subunit of Escherichia coli enterotoxin affects its oligomer formation.
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.
Iida
T
T
Department of Bacteriology and Serology, Osaka University, Japan.
Tsuji
T
T
Honda
T
T
Miwatani
T
T
Wakabayashi
S
S
Wada
K
K
Matsubara
H
H
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
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