Mapping the interaction surface between Caβ 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 Ca1.2 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, Caβ and Caβ, using cross-linking mass spectrometry and protein-protein docking, and uncovered a role in replenishing conduction-defective Ca1.2 channels. Computational and in vitro mutagenesis identified hotspots in Caβ that decreased the affinity for actin but not for Ca1.2. When coexpressed with Ca1.2, none of the tested actin-association-deficient Caβ mutants altered the single-channel properties or the total number of channels at the cell surface. However, coexpression with the Caβ 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 Caβ-actin interaction as a key player for clearing the plasma membrane of corrupted Ca1.2 proteins to ensure the maintenance of a functional pool of channels and proper calcium signal transduction. The Caβ-actin molecular model introduces a potentially druggable protein-protein interface to intervene Ca-mediated signaling processes.