Binding of Bacillus sphaericus binary toxin to a specific receptor on midgut brush‐border membranes from mosquito larvae

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Abstract
The presence of specific receptors for Bacillus sphaericus binary toxin on brush‐border membrane fractions (BBMF) from Culex pipiens larvae midgut cells was demonstrated by an in vitro binding assay. Both activated and radiolabelled polypeptides from the 51‐kDa and 42‐kDa binary toxin of B. sphaericus 1593 specifically bound to BBMF. Direct binding and homologous competition experiments indicated a single class of B. sphaericus toxin receptors, with a dissociation constant (Kd) of approximately 20 nM and a maximum binding capacity (Bmax) of approximately 7 pmol/mg BBMF protein. The sugars GalNAc, GlcNAc and N‐acetyl neuraminic acid had no detectable inhibitory effect on toxin binding to C. pipiens BBMF. Binding experiments with the non‐susceptible mosquito species Aedes aegypti failed to detect significant binding of B. sphaericus binary toxin to A. aegypti BBMF.

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