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