Determinants of α-conotoxin BuIA selectivity on the nicotinic acetylcholine receptor β subunit

Neuronal nicotinic acetylcholine receptors (nAChRs) are pentamers composed of alpha and beta subunits. Different molecular compositions of these subunits constitute various receptor subtypes that are implicated in the pathophysiology and/or treatment of several disease states but are difficult to distinguish pharmacologically. alpha-Conotoxins are a group of small, structurally defined peptides that may be used to molecularly dissect the nAChR-binding site. Heteromeric nAChRs generally contain either a beta 2 or beta 4 subunit in addition to an alpha subunit at the ligand-binding interface. alpha-Conotoxin BuIA kinetically distinguishes between, beta 2- and, beta 4-containing nAChRs, with long off times for the latter. Mutational studies were used to assess the influence of residues that line the putative acetylcholine-binding pocket but differ between, beta 2 and, beta 4 subunits. Residues Thr/Lys59, Val/Ile111, and Phe/Gln119 of the respective, beta 2 and beta 4 subunits are critical to off-rate differences. Among these residues, Thr59 of nAChR beta 2 may interfere with effective access to the binding site, whereas Lys59 may facilitate this binding.