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Isolation and properties of the alpha‐latrotoxin receptor.

The receptor protein of alpha‐latrotoxin (alpha LTx, 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 alpha LTx‐Sepharose. The purified receptor preparation contained four major polypeptides of molecular masses 200 (alpha), 160 (alpha'), 79 (beta) and 43 (gamma) kd according to SDS electrophoresis with molecular ratio alpha 1 alpha' 1 beta 2 gamma 2. The alpha‐ and alpha'‐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 alpha LTx‐binding activity and give closely related peptide maps. Anti‐alpha antibodies recognize the alpha'‐subunit as well. These results suggest that alpha LTx receptor is present in purified preparations in two very close forms containing the alpha‐ or alpha'‐subunit. Beta and gamma proteins do not specifically bind alpha LTx and their physiological role is unclear. They form a complex with solubilized alpha‐ and alpha'‐subunits independently of alpha LTx presence. The receptor proteins were purified to homogeneity by high performance gel filtration in the presence of SDS, their amino acid composition was determined.