Hydrophobic residues at position 10 of α-conotoxin PnIA influence subtype selectivity between α7 and α3β2 neuronal nicotinic acetylcholine receptors
Neuronal nicotinic acetylcholine receptors (nAChRs) are a diverse class of ligand-gated ion channels involved in neurological conditions such as neuropathic pain and Alzheimer's disease. α-Conotoxin [A10L]PnIA is a potent and selective antagonist of the mammalian α7 nAChR with a key binding interaction at position 10. We now describe a molecular analysis of the receptor-ligand interactions that determine the role of position 10 in determining potency and selectivity for the α7 and α3β2 nAChR subtypes. Using electrophysiological and radioligand binding methods on a suite of [A10L]PnIA analogs we observed that hydrophobic residues in position 10 maintained potency at both subtypes whereas charged or polar residues abolished α7 binding. Molecular docking revealed dominant hydrophobic interactions with several α7 and α3β2 receptor residues via a hydrophobic funnel. Incorporation of norleucine (Nle) caused the largest (8-fold) increase in affinity for the α7 subtype (Ki = 44 nM) though selectivity reverted to α3β2 (IC50 = 0.7 nM). It appears that the placement of a single methyl group determines selectivity between α7 and α3β2 nAChRs via different molecular determinants.