PURIFIED OMEGA-CONOTOXIN GVIA RECEPTOR OF RAT-BRAIN RESEMBLES A DIHYDROPYRIDINE-SENSITIVE L-TYPE CALCIUM-CHANNEL

The omega-conotoxin GVIA (CTX) receptor has been purified 1900-fold to apparent homogeneity by monitoring both reversible binding of I-125-labeled CTX (I-125-CTX) and photoincorporation of N-hydroxysuccinimidyl-4-azidobenzoate-I-125-CTX (HSA-I-125-CTX). Photoincorporation of HSA-I-125-CTX into a 230-kDa protein exhibits a pharmacologic and chromatographic profile indicating that the 230-kDa protein is the CTX-binding subunit of the receptor. The pharmacologic specificity of I-125-CTX binding to the purified CTX receptor closely resembles that of the native membrane-bound form with respect to sensitivity towards CTX (K(d) = 32 pM) and other peptide toxin antagonists. The purified CTX receptor comprises the 230-kDa protein (alpha-1) and four additional proteins with apparent molecular masses of 140 (alpha-2), 110, 70 (beta-2), and 60 (beta-1) kDa. This subunit structure closely resembles that of the 1,4-dihydropyridine-sensitive L-type calcium channel.