A Novel Inhibitor of α9α10 Nicotinic Acetylcholine Receptors from Conus vexillum Delineates a New Conotoxin Superfamily

Conotoxins (CTxs) selectively target a range of ion channels and receptors, making them widely used tools for probing nervous system function. Conotoxins have been previously grouped into superfamilies according to signal sequence and into families based on their cysteine framework and biological target. Here we describe the cloning and characterization of a new conotoxin, from Conus vexillum, named aB-conotoxin VxXXIVA. The peptide does not belong to any previously described conotoxin superfamily and its arrangement of Cys residues is unique among conopeptides. Moreover, in contrast to previously characterized conopeptide toxins, which are expressed initially as prepropeptide precursors with a signal sequence, a pro region, and the toxin-encoding region, the precursor sequence of aB-VxXXIVA lacks a pro region. The predicted 40-residue mature peptide, which contains four Cys, was synthesized in each of the three possible disulfide arrangements. Investigation of the mechanism of action of aB-VxXXIVA revealed that the peptide is a nicotinic acetylcholine receptor (nAChR) antagonist with greatest potency against the a9a10 subtype. 1H nuclear magnetic resonance (NMR) spectra indicated that all three aB-VxXXIVA isomers were poorly structured in aqueous solution. This was consistent with circular dichroism (CD) results which showed that the peptides were unstructured in buffer, but adopted partially helical conformations in aqueous trifluoroethanol (TFE) solution. The a9a10 nAChR is an important target for the development of analgesics and cancer chemotherapeutics, and aB-VxXXIVA represents a novel ligand with which to probe the structure and function of this protein.