In silico modeling of toluene binding site in the pore of voltage-gate sodium channel

Thomas RF Scior¹, Evelyn Martínez-Morales², Silvia L Cruz³, Eduardo M Salinas-Stefanon²

¹Departamento de Farmacia; 2Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Ciudad Universitaria, Puebla, Pue, México; ³Departamento de Farmacobiología, CINVESTAV-IPN, Calz. Col. Granjas Coapa, México

Abstract: Toluene is a commonly used organic solvent in commercial products and is sometimes abused as an inhalative hallucinogen, causing arrythmogenic toxicity. At a molecular level we investigated whether a hypothetical interaction model could be devised for the reported myo- and cardiotoxic effects of toluene. Three lines of computed evidence support our hypothesis on the interaction mechanism: (i) Toluene binds at the local anesthetic binding site (LABS), on the wild type (WT) but not on its F1579A mutation, confirming our experimental findings that it inhibits only the WT of skeletal muscle or cardiac isoforms (Na_v 1.4 or 1.5). (ii) Typically for small alkylaryl moiety, multiple binding modes were detected during docking. Toluene is trapped in the tryptophane-rich area at the extracellular vestibule by hydrophobic interaction, mainly π–π stacking, or bound to the LABS with equal binding strength and number of solved poses, mostly by edge-to-face contacts. (iii) The computed loss of toluene binding at the LABS on the mutant model parallels clearly the observed loss of toluene effects on Na_v 1.4. Moreover, we inspected the complete primary sequences with the omitted loops in the 3D models to identify the possible interacting amino acids among the 16% nonidentical ones, and thus confirmed the observed toxicity effects.

Keywords: Toluene, Na⁺ channel, Na_v1.4 isoform, Na_v1.5 isoform, in-silico simulation, cardiotoxicity