LIGAND SPECIFICITY AND AFFINITY OF BT-R-1, THE BACILLUS-THURINGIENSISCRY1A TOXIN RECEPTOR FROM MANDUCA-SEXTA, EXPRESSED IN MAMMALIAN AND INSECT-CELL CULTURES

The Manduca sexta receptor for the Bacillus thuringiensis Cry1Aa, Cry1 Ab, and Cry1Ac toxins, BT-R-1, has been expressed in heterologous cell culture, and its ligand binding characteristics have been determined. When transfected with the BT-R-1 cDNA, insect and mammalian cell cult ures produce a binding protein of approximately 195 kDa, in contrast t o natural BT-R-1 from M. sexta, which has an apparent molecular weight of 210 kDa. Transfection of cultured Spodoptera frugiperda cells with the BT-R-1 cDNA imparts Cry1A-specific high-affinity binding activity typical of membranes prepared from larval ill. sexta midguts. Competi tion assays with BT-R, prepared from larval ill sexta midguts and tran siently expressed in cell culture reveal virtually identical affinitie s for the Cry1Aa, Cry1Ab, and Cry1Ac toxins, clearly demonstrating the absolute specificity of the receptor for toxins of the lepidopteran-s pecific Cry1A family. BT-R-1 therefore remains the only ill. sexta Cry 1A binding protein to be purified, cloned, and functionally expressed in heterologous cell culture, and for the first time, we are able to c orrelate the Cry1Aa, Cry1Ab, and Cry1Ac toxin sensitivities of M. sext a to the identity and ligand binding characteristics of a single midgu t receptor molecule.