Monomer of the B subunit of heat-labile enterotoxin from enterotoxigenic Escherichia coli has little ability to bind to GM1 ganglioside compared to its coligenoid.

Coligenoid, composed of the B subunit of heat-labile enterotoxin from enterotoxigenic Escherichia coli, was separated into monomers in the presence of 2% propionic acid containing 6 M urea (pH 3.8). Monomers equilibrated against 0.75% or 0.5% propionic acid containing 3 M urea (pH 3.8) did not reassemble into coligenoid. Complexes of GM1 ganglioside and coligenoid in these buffers were detected by SDS-polyacrylamide gel electrophoresis, but those of the GM1 ganglioside and monomers were not. The binding ability of monomer to GM1 ganglioside in these buffers was about 1% of that of normal coligenoid by GM1-enzyme-linked immunosorbent assay. Moreover, monomers in these buffers reassembled into coligenoid by buffering against original TEAN buffer, and the binding ability of the resulting coligenoid to GM1 ganglioside was identical to that of native coligenoid. These data suggest that although coligenoid formation is important for the receptor binding of the B subunit, little binding ability to GM1 ganglioside remains in monomer of the B subunit.