Backbone resonance assignments of complexes of apo human calmodulin bound to IQ motif peptides of voltage-dependent sodium channels Na V 1.1, Na V 1.4 and Na V 1.7.

Human voltage-gated sodium (NaV ) channels are critical for initiating and propagating action potentials in excitable cells. Nine isoforms have different roles but similar topologies, with a pore-forming α-subunit and auxiliary transmembrane β-subunits. NaV pathologies lead to debilitating conditions including epilepsy, chronic pain, cardiac arrhythmias, and skeletal muscle paralysis. The ubiquitous calcium sensor calmodulin (CaM) binds to an IQ motif in the C-terminal tail of the α-subunit of all NaV isoforms, and contributes to calcium-dependent pore-gating in some channels. Previous structural studies of calcium-free (apo) CaM bound to the IQ motifs of NaV 1.2, NaV 1.5, and NaV 1.6 showed that CaM binding was mediated by the C-domain of CaM (CaMC ), while the N-domain (CaMN ) made no detectable contacts. To determine whether this domain-specific recognition mechanism is conserved in other NaV isoforms, we used solution NMR spectroscopy to assign the backbone resonances of complexes of apo CaM bound to peptides of IQ motifs of NaV 1.1, NaV 1.4, and NaV 1.7. Analysis of chemical shift differences showed that peptide binding only perturbed resonances in CaMC ; resonances of CaMN were identical to free CaM. Thus, CaMC residues contribute to the interface with the IQ motif, while CaMN is available to interact elsewhere on the channel.