RegIIA: An a4/7-conotoxin from the venom of Conus regius that potently blocks a3ß4 nAChRs

Neuronal nicotinic acetylcholine receptors (nAChRs) play pivotal roles in the central and peripheral nervous systems. They are implicated in disease states such as Parkinson's disease and schizophrenia, as well as addictive processes for nicotine and other drugs of abuse. Modulation of specific nAChRs is essential to understand their role in the CNS. a-Conotoxins, disulfide-constrained peptides isolated from the venom of cone snails, potently inhibit nAChRs. Their selectivity varies markedly depending upon the specific nAChR subtype/a-conotoxin pair under consideration. Thus, a-conotoxins are excellent probes to evaluate the functional roles of nAChRs subtypes. We isolated an a4/7-conotoxin (RegIIA) from the venom of Conus regius. Its sequence was determined by Edman degradation and confirmed by sequencing the cDNA of the protein precursor. RegIIA was synthesized using solid phase methods and native and synthetic RegIIA were functionally tested using two-electrode voltage clamp recording on nAChRs expressed in Xenopus laevis oocytes. RegIIA is among the most potent antagonist of the a3ß4 nAChRs found to date and is also active at a3ß2 and a7 nAChRs. The 3D structure of RegIIA reveals the typical folding of most a4/7-conotoxins. Thus, while structurally related to other a4/7 conotoxins, RegIIA has an exquisite balance of shape, charge, and polarity exposed in its structure to potently block the a3ß4 nAChRs.