A New α-Conotoxin Which Targets α3β2 Nicotinic Acetylcholine Receptors

Abstract

We have isolated a 16-amino acid peptide from the venom of the marine snail Conus magus which potently blocks nicotinic acetylcholine receptors (nAChRs) composed of α3β2 subunits. This peptide, named α-conotoxin MII, was identified by electrophysiologically screening venom fractions against cloned nicotinic receptors expressed in Xenopus oocytes. The peptide's structure, which has been confirmed by mass spectrometry and total chemical synthesis, differs significantly from those of all previously isolated α-conotoxins. Disulfide bridging, however, is conserved. The toxin blocks the response to acetylcholine in oocytes expressing α3β2 nAChRs with an IC50 of 0.5 nM and is 2-4 orders of magnitude less potent on other nAChR subunit combinations. We have recently reported the isolation and characterization of α-conotoxin ImI, which selectively targets homomeric α7 neuronal nAChRs. Yet other α-conotoxins selectively block the muscle subtype of nAChR. Thus, it is increasingly apparent that α-conotoxins represent a significant resource for ligands with which to probe structure-function relationships of various nAChR subtypes. We have isolated a 16-amino acid peptide from the venom of the marine snail Conus magus which potently blocks nicotinic acetylcholine receptors (nAChRs) composed of α3β2 subunits. This peptide, named α-conotoxin MII, was identified by electrophysiologically screening venom fractions against cloned nicotinic receptors expressed in Xenopus oocytes. The peptide's structure, which has been confirmed by mass spectrometry and total chemical synthesis, differs significantly from those of all previously isolated α-conotoxins. Disulfide bridging, however, is conserved. The toxin blocks the response to acetylcholine in oocytes expressing α3β2 nAChRs with an IC50 of 0.5 nM and is 2-4 orders of magnitude less potent on other nAChR subunit combinations. We have recently reported the isolation and characterization of α-conotoxin ImI, which selectively targets homomeric α7 neuronal nAChRs. Yet other α-conotoxins selectively block the muscle subtype of nAChR. Thus, it is increasingly apparent that α-conotoxins represent a significant resource for ligands with which to probe structure-function relationships of various nAChR subtypes.