A Cation-π Interaction Discriminates among Sodium Channels That Are Either Sensitive or Resistant to Tetrodotoxin Block

摘要: Voltage-gated sodium channels control the upstroke of action potential in excitable cells nerve and muscle tissue, making them ideal targets for exogenous toxins that aim to squelch electrical excitability. One such toxin, tetrodotoxin (TTX), blocks with nanomolar affinity only when an aromatic Phe or Tyr residue is present at a specific location external vestibule ion-conducting pore. To test whether TTX attracted Tyr401 NaV1.4 through cation-{pi} interaction, this was replaced fluorinated derivatives using vivo nonsense suppression. Consistent increased fluorination Phe401, which reduces negative electrostatic on face, caused monotonic increase inhibitory constant block. Trifluorination ring decreased by ~50-fold, reduction similar replacement comparably hydrophobic Leu. Furthermore, we show energetically equivalent interaction underlies both use-dependent tonic block TTX. Our results are supported high level ab initio quantum mechanical calculations applied model binding benzene. analysis suggests side chain faces permeation pathway where it orients optimally interacts permeant ions. These first their kind incorporation unnatural amino acids into voltage-gated channel demonstrate responsible obligate nature position TTX-sensitive channels.