(709g) Informing the Structural Model of the Mammalian Voltage-Gated Sodium Ion Channel: Probing Protein Conformational Dynamics Using Small-Molecule Neurotoxins

Voltage-gated sodium ion channels (Na_Vs) are critical to life, being responsible for generating action potentials in skeletal muscle, nerve, and cardiac cells.[1] The abnormal expression and/or malfunction of Na_Vs is tied to epilepsy,arrhythmia,intractable acute and chronic pain, metastatic cancers, erythromelalgia,and congenital insensitivity to pain.[1,2] Despite their importance to human function and disease, a complete understanding of the conformational dynamics of Na_Vs, their responsiveness to changes in membrane potential, and the influence of small molecules on ion gating remains elusive.Critical to the understanding of Na_V function is the construction of a detailed model of the tertiary structure of the pore forming and voltage-sensing domains. As such, ligand docking studies using the small molecule neurotoxins veratridine [partial agonist, 3] and batrachotoxin [agonist, 4] with a homology model of Na_V, based on the crystal structure of a prokaryotic Na_V [5], have been performed. These computational modeling studies have allowed for the assignment an overlapping putative binding site for both toxins within the ion pore. Chemical synthesis has enabled the construction of de novo synthetic and semisynthetic neurotoxin analogs. In combination with protein mutagenesis, the systematic exploration of the inner pore of Na_V has confirmed the binding site proposed by the model. Although these results are in agreement with other reported experimental findings, they directly refute a previously proposed pharmacophore model for veratridine and batrachotoxin. Additionally, these studies have revealed a previously unreported state-dependent functional duality of veratridine as either a partial agonist or antagonist. The continued exploration of Na_V-ligand interaction will inform Na_V homology modeling and improve the understanding of Na_V dynamics.

[1] Nardi, A.; Damann, N.; Hertrampf, T.; Kless, A. ChemMedChem 2012, 7, 1712.

[2] Martin, F.; Ufodiama, C.; Watt, I.; Bland, M.; Brackenbury, W. J. Front. Pharamcol. 2015, 6, 273.

[3] (a) Rando, T. A. J. Gen. Physiol. 1989, 93, 43. (b) Codding, P. W. J. Am. Chem. Soc. 1983, 105, 3172.

[4] (a) Khodorov, B. I. Prog. Biophys. Molec. Biol. 1985, 45, 57. (b) Daly, J. W.; Witkop, B.; Bommer, P.; Biemann, K. J. Am. Chem. Soc. 1965, 87, 124.

[5] McCusker, E. C.; Bagneris, C.; Naylor, C. E.; Cole, A. R.; Dâ??Avanzo, N.; Nichols, C. G.; Wallace, B. A. Nat. Commun. 2012, 3, 1102.