Solving the α-conotoxin folding problem: efficient selenium-directed on-resin generation of more potent and stable nicotinic acetylcholine receptor antaqonists
α-Conotoxins are tightly folded miniproteins that antagonize nicotinic acetylcholine receptors (nAChR) with high specificity for diverse subtypes. Here we report the use of selenocysteine in a supported phase method to direct native folding and produce α-conotoxins efficiently with improved biophysical properties. By replacing complementary cysteine pairs with selenocysteine pairs on an amphiphilic resin, we were able to chemically direct all five structural subclasses of α-conotoxins exclusively into their native folds. X-ray analysis at 1.4 Å resolution of α-selenoconotoxin PnIA confirmed the isosteric character of the diselenide bond and the integrity of the α-conotoxin fold. The α-selenoconotoxins exhibited similar or improved potency at rat diaphragm muscle and α3β4, α7, and α1β1δγ nAChRs expressed in Xenopus oocytes plus improved disulfide bond scrambling stability in plasma. Together, these results underpin the development of more stable and potent nicotinic antagonists suitable for new drug therapies, and highlight the application of selenocysteine technology more broadly to disulfide-bonded peptides and proteins.