BRAIN ALPHA-BUNGAROTOXIN BINDING-PROTEIN CDNAS AND MABS REVEAL SUBTYPES OF THIS BRANCH OF THE LIGAND-GATED ION CHANNEL GENE SUPERFAMILY

α-Bungarotoxin (αBgt) is a potent, high-affinity antagonist for nicotinic acetylcholine receptors (AChRs) from muscle, but not for AChRs from neurons. Both muscle and neuronal AChRs are thought to be formed from multiple homologous subunits aligned around a central cation channel whose opening is regulated by ACh binding. In contrast, the exact structure and function of high-affinity αBgt binding proteins (αBgtBPs) found in avian and mammalian neurons remain unknown. Here we show that cDNA clones encoding αBgtBP α1 and α2 subunits define αBgtBPs as members of a gene family within the ligand-gated ion channel gene superfamily, but distinct from the gene families of AChRs from muscles and nerves. Subunit-specific monoclonal antibodies raised against bacterially expressed αBgtBP α1 and α2 subunit fragments reveal the existence of at least two different αBgtBP subtypes in embryonic day 18 chicken brains. More than 75% of all αBgtBPs have the α1 subunit, but no α2 subunit, and a minor αBgtBP subtype (∼15%) has both the α1 and α2 subunits. © 1990.