Binary Architecture of the Nav1.2-β2 Signaling Complex

Abstract

β-subunits can influence voltage-gated sodium (Nav) channel function; yet, the working mechanisms remain unclear which hampers our insights into how β-subunit mutations relate to disorders. To begin to understand this causal relationship, we examined β-subunit interactions with Nav1.2 by solving the crystal structure of the β2 extracellular domain at 1.35A. We identified a flexible loop formed by 72Cys and 75Cys, a unique feature among β-subunit isoforms. Moreover, we found that 55Cys determines the influence of β2 on Nav1.2 toxin susceptibility. Further mutagenesis combined with the use of spider toxins reveals that 55Cys forms a disulfide bond with 910Cys in the Nav1.2 domain II pore loop, thereby suggesting a 1:1 stoichiometry. Finally, our results provide clues as to which disulfide bonds are formed between adjacent Nav1.2 912/918Cys residues. The concepts emerging from this work will help lay the foundation for a model reflecting the β-subunit location in a Nav channel complex.