Re‐engineering the μ‐conotoxin SIIIA scaffold

Voltage‐gated sodium (Na_v) channels are responsible for generation and propagation of action potentials throughout the nervous system. Their malfunction causes several disorders and chronic conditions including neuropathic pain. Potent subtype specific ligands are essential for deciphering the molecular mechanisms of Na_v channel function and development of effective therapeutics. µ‐Conotoxin SIIIA is a potent mammalian Na_v1.2 channel blocker that exhibits analgesic activity in rodents. We undertook to reengineer loop 1 through a strategy involving charge alterations and truncations which led to the development of µ‐SIIIA mimetics with novel selectivity profiles. A novel N5K/D15A]SIIIA(3–20) mutant with enhanced net positive charge showed a dramatic increase in its Na_v1.2 potency (IC₅₀ of 0.5 nM vs. 9.6 nM for native SIIIA) though further truncations led to loss of potency. Unexpectedly, it appears that SIIIA loop 1 significantly influences its Na_v channel interactions despite loop 2 and 3 residues constituting the pharmacophore. This minimal functional conotoxin scaffold may allow further development of selective Na_V blockers. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 347–354, 2014.