The proteolytically cleaved distal C-terminal domain acts as a potent autoinhibitor of Ca(V)1.2 channel function by forming a specific molecular complex with the truncated alpha(1) subunit.
The study reveals a unique regulatory mechanism where proteolytic processing of the CaV1.2 channel produces a distal C-terminal domain that acts as a potent autoinhibitor of channel function.
Voltage-gated Ca(2+) channels of the Ca(V)1 family initiate excitation-contraction coupling in cardiac, smooth, and skeletal muscle and are primary targets for regulation by the sympathetic nervous system in the 'fight-or-flight' response. In the heart, activation of beta-adrenergic receptors greatly increases the L-type Ca(2+) current through Ca(V)1.2 channels, which requires phosphorylation by cyclic AMP-dependent protein kinase (PKA) anchored via an A-kinase anchoring protein (AKAP15). Surprisingly, the site of interaction of PKA and AKAP15 lies in the distal C-terminus, which is cleaved from the remainder of the channel by in vivo proteolytic processing. Here we report that the proteolytically cleaved distal C-terminal domain forms a specific molecular complex with the truncated alpha(1) subunit and serves as a potent autoinhibitory domain. Formation of the autoinhibitory complex greatly reduces the coupling efficiency of voltage sensing to channel opening and shifts the voltage dependence of activation to more positive membrane potentials. Ab initio structural modelling and site-directed mutagenesis revealed a binding interaction between a pair of arginine residues in a predicted alpha-helix in the proximal C-terminal domain and a set of three negatively charged amino acid residues in a predicted helix-loop-helix bundle in the distal C-terminal domain. Disruption of this interaction by mutation abolished the inhibitory effects of the distal C-terminus on Ca(V)1.2 channel function. These results provide the first functional characterization of this autoinhibitory complex, which may be a major form of the Ca(V)1 family Ca(2+) channels in cardiac and skeletal muscle cells, and reveal a unique ion channel regulatory mechanism in which proteolytic processing produces a more effective autoinhibitor of Ca(V)1.2 channel function.
Hulme et al. (2006) studied this question. Proteolytically cleaved distal C-terminal domain vs. Mutated distal C-terminus was evaluated on Ca(V)1.2 channel function and voltage dependence of activation. The proteolytically cleaved distal C-terminal domain acts as a potent autoinhibitor of Ca(V)1.2 channel function by forming a specific molecular complex with the truncated alpha(1) subunit.
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