Molecular Basis for Differential Sensitivity of α-Conotoxin RegIIA at Rat and Human Neuronal Nicotinic Acetylcholine Receptors.

α-Conotoxins, as nicotinic acetylcholine receptor (nAChR) antagonists, are powerful tools for dissecting biologic processes and guiding drug development. The α3β2 and α3β4 nAChR subtypes are expressed in the central and peripheral nervous systems and play a critical role in various pathophysiological conditions ranging from nicotine addiction to the development and progression of lung cancer. Here we used the α4/7-conotoxin RegIIA, a disulfide-bonded peptide from the venom of Conus regius, and its analog [N11A,N12A]RegIIA to probe the specific pharmacological properties of rat and human nAChR subtypes. nAChR subtypes were heterologously expressed in Xenopus oocytes and two-electrode voltage clamp recordings used to investigate the effects of the peptides on nAChR activity. RegIIA potently inhibited currents evoked by acetylcholine (ACh) at rat α3β2 (IC50 = 10.7 nM), whereas a 70-fold lower potency was observed at human α3β2 nAChR (IC50 = 704.1 nM). Conversely, there were no species-specific differences in sensitivity to RegIIA at the α3β4 nAChR. Receptor mutagenesis and molecular dynamics studies revealed that this difference can be attributed primarily to a single amino acid change: Glu198 on the rat α3 subunit corresponding to a proline on the human subunit. These findings reveal a novel species- and subunit-specific receptor-antagonist interaction.