δ-Conotoxins Synthesized Using an Acid-cleavable Solubility Tag Approach Reveal Key Structural Determinants for NaV Subtype Selectivity*

Background: Conotoxins are marine snail venom peptides of interest as pharmacological tools and potential medicines. Results: δ-Conotoxins are poorly understood because they are difficult to synthesize. Using a new synthesis approach, we readily produced three δ-conotoxins and two analogs, obtaining new pharmacological insights. Conclusion: Key structures on δ-conotoxins determine NaV subtype selectivity. Significance: Our synthesis approach is applicable to other similarly challenging peptides. Conotoxins are venom peptides from cone snails with multiple disulfide bridges that provide a rigid structural scaffold. Typically acting on ion channels implicated in neurotransmission, conotoxins are of interest both as tools for pharmacological studies and as potential new medicines. δ-Conotoxins act by inhibiting inactivation of voltage-gated sodium channels (Nav). Their pharmacology has not been extensively studied because their highly hydrophobic character makes them difficult targets for chemical synthesis. Here we adopted an acid-cleavable solubility tag strategy that facilitated synthesis, purification, and directed disulfide bridge formation. Using this approach we readily produced three native δ-conotoxins from Conus consors plus two rationally designed hybrid peptides. We observed striking differences in Nav subtype selectivity across this group of compounds, which differ in primary structure at only three positions: 12, 23, and 25. Our results provide new insights into the structure-activity relationships underlying the Nav subtype selectivity of δ-conotoxins. Use of the acid-cleavable solubility tag strategy should facilitate synthesis of other hydrophobic peptides with complex disulfide bridge patterns.