αA-Conotoxin OIVA defines a new αA-conotoxin subfamily of nicotinic acetylcholine receptor inhibitors

Abstract

The venoms of cone snails are rich in multiply disulfide-crosslinked peptides, the conotoxins. Conotoxins are grouped into families on the basis of shared cysteine patterns and homologous molecular targets. For example, both the κA- and αA-conotoxin families share the same Class IV Cys pattern (–CC–C–C–C–C–), but differ in their molecular targets. The κA-conotoxins are excitatory toxins that purportedly block potassium channels, while the αA-conotoxins are paralytic conotoxins that inhibit nicotinic acetylcholine receptors (nAChRs). In this work, we describe the isolation and characterization of a novel Conus peptide from venom milked from Hawaiian specimens of Conus obscurus. This peptide shares the Class IV Cys pattern but differs from both previously characterized αA- and κA-conotoxins in the spacing of amino acids between Cys resides. However, the peptide is similar to previously characterized αA-conotoxins in its paralytic effects on fish and its antagonist activity on the neuromuscular nAChR. Unexpectedly, the peptide differs in its disulfide bonding from αA-conotoxin PIVA. We have named this unique peptide αA-conotoxin OIVA, and we consider it the defining member of a subfamily of αA-conotoxins that we designate the αA (1–3)-conotoxins to identify them by their unique disulfide bonding framework. These results indicate that the αA-conotoxin family is both more structurally diverse and broadly distributed than previously believed.