A novel 4/6-type alpha-conotoxin ViIA selectively inhibits nAchR α3β2 subtype

Conotoxins (CTxs) are typically small peptides composed of 12-50 amino acid residues with 2-5 disulfide bridges. Most of them potently and selectively target a wide variety of ion channels and membrane receptors. They are highly valued as neuropharmacological probes and in pharmaceutical development. In this work, a novel alpha 4/6-CTx named ViIA (RDCCSNPPCAHNNPDC-NH2) was identified from a cDNA library of the venom ducts of Conus virgo (C. virgo). ViIA was then synthesized chemically and its disulfide connectivity was identified as 'C-1-C-3, C-2-C-4'. Its molecular targets were further assessed using two-electrode voltage clamping. The results indicated that ViIA selectively inhibited nicotinic acetylcholine receptor (nAChR) alpha 3 beta 2 subtype with an IC50 of 845.5 nM, but did not target dorsal root ganglion sodium (Na+)-, potassium (K+)-or calcium (Ca2+)-ion channels. Further structure-activity relationship analysis demonstrated that Arg(1) and His(11) but not Asp(2) were the functional residues. To the best of our knowledge, ViIA is the first 4/6 alpha-CTx that selectively inhibits nAChR alpha 3 beta 2 subtype. This finding expands the knowledge of targets of alpha 4/6-family CTxs.