Cross-kingdom auxiliary subunit modulation of a voltage-gated sodium channel

Voltage-gated, sodium ion-selective channels (Na_V) generate electrical signals contributing to the upstroke of the action potential in animals. Na_Vs are also found in bacteria and are members of a larger family of tetrameric voltage-gated channels that includes Ca_Vs, K_Vs, and Na_Vs. Prokaryotic Na_Vs likely emerged from a homotetrameric Ca²⁺-selective voltage-gated progenerator, and later developed Na⁺ selectivity independently. The Na_V signaling complex in eukaryotes contains auxiliary proteins, termed beta (β) subunits, which are potent modulators of the expression profiles and voltage-gated properties of the Na_V pore, but it is unknown whether they can functionally interact with prokaryotic Na_V channels. Herein, we report that the eukaryotic Na_Vβ1-subunit isoform interacts with and enhances the surface expression as well as the voltage-dependent gating properties of the bacterial Na_V, NaChBac in Xenopus oocytes. A phylogenetic analysis of the β-subunit gene family proteins confirms that these proteins appeared roughly 420 million years ago and that they have no clear homologues in bacterial phyla. However, a comparison between eukaryotic and bacterial Na_V structures highlighted the presence of a conserved fold, which could support interactions with the β-subunit. Our electrophysiological, biochemical, structural, and bioinformatics results suggests that the prerequisites for β-subunit regulation are an evolutionarily stable and intrinsic property of some voltage-gated channels.