Identification of residues in the adult nicotinic acetylcholine receptor that confer selectivity for curariform antagonists

We identify residues in the epsilon and delta subunits of the adult nicotinic acetylcholine receptor that give the alpha epsilon and alpha delta binding sites different affinities for the curariform antagonist dimethyl d-tubocurarine (DMT). By constructing epsilon-delta subunit chimeras, coexpressing them with complementary subunits, and measuring DMT binding, we identify two pairs of residues, Ile(epsilon 58)/His(delta 60) and Asp(epsilon 59)/Ala(delta 61), responsible for DMT site selectivity in the adult receptor. The two determinants contribute approximately equally to the binding site and interact in contributing to the site. Exchange of these residues from one subunit to the other exchanges the affinities of the resulting binding sites. These determinants in the adult receptor are far from those that confer site selectivity in the fetal receptor; determinants in the fetal receptor are Ile(gamma 116)/Val(delta 118), Tyr(gamma 117)/Thr(delta 119), and Ser(gamma 161)/Lys(delta 163). Thus, alternative residues confer DMT selectivity in fetal and adult acetylcholine receptors.