Definition and Characterization of the Short αA-Conotoxins:  A Single Residue Determines Dissociation Kinetics from the Fetal Muscle Nicotinic Acetylcholine Receptor

We report the definition and characterization of a conotoxin subfamily, designated the short αA-conotoxins (αAS) and demonstrate that all of these share the unique property of selectively antagonizing the fetal subtype of the mammalian neuromuscular nicotinic acetylcholine receptor (nAChR). We have characterized newly identified αAS-conotoxins from Conus pergrandis and have conducted a more detailed characterization of αA-conotoxins previously reported from additional Conus species. Among the results, the characterization of the short αA-conotoxins revealed diverse kinetics of a block of the fetal muscle nAChR, particularly in dissociation rates. The structure−function relationships of native αAS-conotoxins and some analogues revealed a single amino acid locus (alternatively either His or Pro in native peptides) that is a critical determinant of the dissociation kinetics. The unprecedented binding selectivity for the fetal muscle nAChR, coupled with the kinetic diversity, should make αAS-conotoxins useful ligands for a diverse set of studies. The rapidly reversible peptides may be most suitable for electrophysiological studies, while the relatively irreversible peptides should be most useful for binding and localization studies.