Key result
Structural differences in the proximal linker regions of CaV1.2 and CaV2.2 dictate distinct voltage- and calcium-dependent inactivation kinetics, demonstrating the intrinsic role of the I-II linker in voltage-dependent calcium channel function.
The I-II linker of voltage-dependent calcium channels plays an intrinsic role in channel function and inactivation, independent of the Ca(V)β subunit.
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Establishes I-II linker as β-independent CaV regulator; leaves open its targeting in cardiac channelopathies.
Voltage-dependent calcium channels (VDCCs) allow the passage of Ca(2+) ions through cellular membranes in response to membrane depolarization. The channel pore-forming subunit, α1, and a regulatory subunit (Ca(V)β) form a high affinity complex where Ca(V)β binds to a α1 interacting domain in the intracellular linker between α1 membrane domains I and II (I-II linker). We determined crystal structures of Ca(V)β2 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 Å, respectively. Structural differences between the highly conserved linkers, important for coupling Ca(V)β 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)β, 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.
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Almagor et al. (2012) studied this question. Mutations in CaV1.2 and CaV2.2 I-II linkers vs. Wild-type channels was evaluated on Channel inactivation kinetics and voltage dependence of activation. Structural differences in the proximal linker regions of CaV1.2 and CaV2.2 dictate distinct voltage- and calcium-dependent inactivation kinetics, demonstrating the intrinsic role of the I-II linker in voltage-dependent calcium channel function.
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