Mapping the interaction surface between CaVβ and actin and its role in calcium channel clearance

Defective ion channel turnover and clearance of damaged proteins are associated with aging and neurodegeneration. The L-type CaV1.2 voltage-gated calcium channel mediates depolarization-induced calcium signals in heart and brain. Here, we determined the interaction surface between actin and two calcium channel subunits, CaVβ2 and CaVβ4, using cross-linking mass spectrometry and protein-protein docking, and uncovered a role in replenishing conduction-defective CaV1.2 channels. Computational and in vitro mutagenesis identified hotspots in CaVβ that decreased the affinity for actin but not for CaV1.2. When coexpressed with CaV1.2, none of the tested actin-association-deficient CaVβ mutants altered the single-channel properties or the total number of channels at the cell surface. However, coexpression with the CaVβ2 hotspot mutant downregulated current amplitudes, and with a concomitant reduction in the number of functionally available channels, indicating that current inhibition resulted from a build-up of conduction silent channels. Our findings established CaVβ2-actin interaction as a key player for clearing the plasma membrane of corrupted CaV1.2 proteins to ensure the maintenance of a functional pool of channels and proper calcium signal transduction. The CaVβ-actin molecular model introduces a potentially druggable protein-protein interface to intervene CaV-mediated signaling processes.