Isolation, characterization and total regioselective synthesis of the novel μO-conotoxin MfVIA from Conus magnificus that targets voltage-gated sodium channels

The mu O-conotoxins are notable for their unique selectivity for Na(v)1.8 over other sodium channel isoforms, making them attractive drug leads for the treatment of neuropathic pain. We describe the discovery of a novel mu O-conotoxin, MfVIA, from the venom of Conus magnificus using high-throughput screening approaches. MfVIA was found to be a hydrophobic 32-residue peptide (amino acid sequence RDCQEKWEYCIVPILGFVYCCPGLICGPFVCV) with highest sequence homology to mu O-conotoxin MrVIB. To overcome the synthetic challenges posed by mu O-conotoxins due to their hydrophobic nature and difficult folding, we developed a novel regioselective approach for the synthesis of mu O-conotoxins. Performing selective oxidative deprotections of the cysteine side-chain protecting groups of the fully protected peptide allowed manipulations in organic solvents with no chromatography required between steps. Using this approach, we obtained correctly folded MfVIA with increased synthetic yields. Biological activity of MfVIA was assessed using membrane potential-sensitive dyes and electrophysiological recording techniques. MfVIA preferentially inhibits Na(v)1.8 (IC50 95.9 +/- 74.3 nM) and Na(v)1.4 (IC50 81 +/- 16 nM), with significantly lower affinity for other Na-v subtypes (IC50 431-6203 nM; Na(v)1.5 > 1.6 similar to 1.7 similar to 1.3 similar to 1.1 similar to 1.2). This improved approach to mu O-conotoxin synthesis will facilitate the optimization of mu O-conotoxins as novel analgesic molecules to improve pain management. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.