Half-calcified calmodulin promotes basal activity and inactivation of the L-type calcium channel CaV1.2.

The L-type Ca2+ channel CaV1.2 controls gene expression, cardiac contraction, and neuronal activity. Calmodulin (CaM) governs CaV1.2 open probability (Po) and Ca2+-dependent inactivation (CDI) but the mechanisms remain unclear. Here, we present electrophysiological data that identify a half Ca2+-saturated CaM species (Ca2/CaM) with Ca2+ bound solely at the third and fourth EF-hands (EF3 and EF4) under resting Ca2+ concentrations (50-100 nM) that constitutively preassociates with CaV1.2 to promote Po and CDI. We also present an NMR structure of a complex between the CaV1.2 IQ motif (residues 1644-1665) and Ca2/CaM12', a calmodulin mutant in which Ca2+ binding to EF1 and EF2 is completely disabled. We found that the CaM12' N-lobe does not interact with the IQ motif. The CaM12' C-lobe bound two Ca2+ ions and formed close contacts with IQ residues I1654 and Y1657. I1654A and Y1657D mutations impaired CaM binding, CDI, and Po, as did disabling Ca2+ binding to EF3 and EF4 in the CaM34 mutant when compared to WT CaM. Accordingly, a previously unappreciated Ca2/CaM species promotes CaV1.2 Po and CDI, identifying Ca2/CaM as an important mediator of Ca signaling.

Chemical shift assignments of the C-terminal domain of CaBP1 bound to the IQ-motif of voltage-gated Ca2+ channel (CaV1.2).

The neuronal L-type voltage-gated Ca2+ channel (CaV1.2) interacts with Ca2+ binding protein 1 (CaBP1), that promotes Ca2+-induced channel activity. The binding of CaBP1 to the IQ-motif in CaV1.2 (residues 1644-1665) blocks the binding of calmodulin and prevents Ca2+-dependent inactivation of CaV1.2. This Ca2+-induced binding of CaBP1 to CaV1.2 is important for modulating neuronal synaptic plasticity, which may serve a role in learning and memory. Here we report NMR assignments of the C-terminal domain of CaBP1 (residues 99-167, called CaBP1C) that contains two Ca2+ bound at the third and fourth EF-hands (EF3 and EF4) and is bound to the CaV1.2 IQ-motif from CaV1.2 (BMRB accession no. 51518).

Chemical shift assignments of a calmodulin intermediate with two Ca2+ bound in complex with the IQ-motif of voltage-gated Ca2+ channels (CaV1.2).

Calcium-dependent inactivation (CDI) of neuronal voltage-gated Ca2+ channels (CaV1.2) is important for synaptic plasticity, which is associated with learning and memory. The Ca2+-dependent binding of calmodulin (CaM) to CaV1.2 is essential for CDI. Here we report NMR assignments for a CaM mutant (D21A/D23A/D25A/E32Q/D57A/D59A/N61A/E68Q, called CaMEF12) that contains two Ca2+ bound at the third and fourth EF-hands (EF3 and EF4) and is bound to the IQ-motif (residues 1644-1665) from CaV1.2 (BMRB accession no. 27692).