Hydrophobic residues at position 10 of a-conotoxin PnIA influence subtype selectivity between a7 and a3ß2 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. alpha-Conotoxin [A10L]PnIA is a potent and selective antagonist of the mammalian alpha 7 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 alpha 7 and alpha 3 beta 2 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 alpha 7 binding. Molecular docking revealed dominant hydrophobic interactions with several alpha 7 and alpha 3 beta 2 receptor residues via a hydrophobic funnel. Incorporation of norleucine (Nle) caused the largest (8-fold) increase in affinity for the alpha 7 subtype (Ki = 44 nM) though selectivity reverted to alpha 3 beta 2 (IC50 = 0.7 nM). It appears that the placement of a single methyl group determines selectivity between alpha 7 and alpha 3 beta 2 nAChRs via different molecular determinants. Crown Copyright