The Role of a Voltage-Dependent Ca2+ Channel Intracellular Linker: A Structure-Function Analysis

Voltage-dependent calcium channels (VDCCs) allow the passage of Ca2+ ions through cellular membranes in response to membrane depolarization. The channel pore-forming subunit, alpha 1, and a regulatory subunit (Ca-V beta) form a high affinity complex where Ca-V beta binds to a alpha 1 interacting domain in the intracellular linker between alpha 1 membrane domains I and II (I-II linker). We determined crystal structures of Ca-V beta 2 functional core in complex with the Ca(V)1.2 and Ca(V)2.2 I-II linkers to a resolution of 1.95 and 2.0 angstrom, respectively. Structural differences between the highly conserved linkers, important for coupling Ca-V beta to the channel pore, guided mechanistic functional studies. Electrophysiological measurements point to the importance of differing linker structure in both Ca(V)1 and 2 subtypes with mutations affecting both voltage- and calcium-dependent inactivation and voltage dependence of activation. These linker effects persist in the absence of Ca-V beta, pointing to the intrinsic role of the linker in VDCC function and suggesting that I-II linker structure can serve as a brake during inactivation.