Molecular basis for the differential sensitivity of rat and human α9α10 nAChRs to α-conotoxin RgIA

J. Neurochem. (2012) 122, 11371144. Abstract The a9a10 nicotinic acetylcholine receptor (nAChR) may be a potential target in pathophysiology of the auditory system, chronic pain, and breast and lung cancers. Alpha-conotoxins, from the predatory marine snail Conus, are potent nicotinic antagonists, some of which are selective for the a9a10 nAChR. Here, we report a two order of magnitude species difference in the potency of a-conotoxin RgIA for the rat versus human a9a10 nAChR. We investigated the molecular mechanism of this difference. Heterologous expression of the rat a9 with the human a10 subunit in Xenopus oocytes resulted in a receptor that was blocked by RgIA with potency similar to that of the rat a9a10 nAChR. Conversely, expression of the human a9 with that of the rat a10 subunit resulted in a receptor that was blocked by RgIA with potency approaching that of the human a9a10 receptor. Systematic substitution of residues found in the human a9 subunit into the homologous position in the rat a9 subunit revealed that a single point mutation, Thr56 to Ile56, primarily accounts for this species difference. Remarkably, although the a9 nAChR subunit has previously been reported to provide the principal (+) binding face for binding of RgIA, Thr56 is located in the (-) complementary binding face.