β4 Modulates NaV1.2 Toxin Pharmacology

Abstract

The voltage-gated sodium (Nav) channel signaling complex contains up to four distinct beta-subunits (β1-β4) that influence the functional properties of the pore-forming alpha-subunit. While investigating whether beta-subunits also influence ligand interactions, we found that β4 can drastically alter the response of the neuronal rNav1.2a isoform to spider and scorpion toxins that target paddle motifs within Nav channel voltage sensors. In conjunction with the β4 crystal structure, we utilized the altered sensitivity to a tarantula toxin as a tool to probe the interaction between rNav1.2a and β4. As a result, we identified 58Cys as an exposed residue that when mutated eliminates the influence of β4 on rNav1.2a toxin pharmacology. In addition, we exploited β4-induced alterations in toxin sensitivity to probe the interaction between rNav1.2a and a β4 mutant that mimics a β1 mutation implicated in epilepsy (C121W). We found that although this mutant still folds and traffics to the membrane, its interaction with the Nav channel is lost. The principles emerging from this work: 1) help explain tissue-dependent variations in Nav channel pharmacology; 2) enable the mechanistic interpretation of beta-subunit-related disorders; and 3) provide new opportunities to design molecules capable of correcting aberrant beta-subunit behavior.