ISOLATION AND PROPERTIES OF THE ALPHA-IATROTOXIN RECEPTOR

The receptor protein of α-latrotoxin (αLTx, a neurotoxin with 'pure' presynaptic action isolated from black widow spider venom), was solubilized by Triton X-100 from bovine brain membranes and purified by affinity chromatography on αLTx-Sepharose. The purified receptor preparation contained four major polypeptides of molecular masses 200 (}, 160 (α'), 79 (β) and 43 (γ) kd according to SDS electrophoresis with molecular ratio α1α(2γ2 1/2 ). The α- and α'-subunits are glycoproteins binding to wheat germ lectin and can be separated under non-denaturing conditions by anion exchange chromatography. Purified to homogeneity, both of them, though differing in the carbohydrate composition, retain the αLTx-binding activity and give closely related peptide maps. Anti-α antibodies recognize the α'-subunits as well. These results suggest that αLTx receptor is present in purified preparations in two very close forms containing the α- or α'-subunit. β and γ proteins do not specifically bind αLTx and their physiological role is unclear. They form a complex with solubilized α- and α'-subunits independently of αLTx presence. The receptor proteins were purified to homogeneity by high performance gel filtration in the presence of DS, their amino acid composition was determined.