IDENTIFICATION OF BOMBYX-MORI MIDGUT RECEPTOR FOR BACILLUS-THURINGIENSIS INSECTICIDAL CRYIA(A) TOXIN

As part of a study of the mechanism by which Bacillus thuringiensis in secticidal crystal protein acts, a Bombyx mori receptor to the CryIA(a ) toxin specific for lepidopterans was examined. Histological examinat ion show-ed that the toxin acted on the brush-border membrane of the m idgut columnar cells and broke its infolding structure, causing cell l ysis. The membrane vesicles were purified, and a 175-kDa protein bindi ng the toxin was found that accounted for some 0.015% of membrane prot eins. The protein, designated BtR175, was a glycoprotein that reacted with coracanavalin A. Anti-BtR antibodies inhibited the binding of tox in to membrane vesicles in vitro and decreased the effect of the toxin to silkworms in vivo. BtR175, although found in the gut, was not foun d in fat bodies, integument, or silk glands. These results indicated t hat BtR175 was the receptor protein for the insecticidal toxin. Protei ns (137 and 107 kDa) binding the CryIA(a) toxin also were found in the gut membranes of Tenebrio moritor larvae, a coleopteran not sensitive to the toxin, The specificity of the toxin could not be explained onl y in term of the existence of its binding protein.