title: A novel calmodulin site in the Cav1.2 N-terminus regulates calcium-dependent inactivation.
abstract: The L-type voltage-gated calcium channel Cav1.2 is important for excitation-contraction coupling in the heart, as well as CREB-mediated transcription in the brain. The ubiquitous calcium-binding protein calmodulin (CaM) is known to modulate calcium-dependent inactivation (CDI) of these channels, thus limiting the amount of calcium entering via Cav1.2 during prolonged or repetitive membrane depolarizations. The proximal N-terminus of Cav1.2 contains a CaM-binding site at residue W52 that is critical for a type of CDI that is mediated by the N-terminal lobe of CaM. Here, we identify a second CaM interaction site in the Cav1.2 N-terminus downstream of the W52 site that is formed by residue C106. We show by site-directed mutagenesis coupled with electrophysiological measurements that this region of the channel functionally partakes in N-lobe CDI, likely by acting as a gating transduction motif. Thus, our data indicate that calcium regulation of Cav1.2 channels is more complex than previously thought, and involves more than one region within the channel's N-terminal domain.
authors.affiliation: Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4N1, Canada.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Simms
authors.forename: Ivana Assis
authors.initials: IA
authors.lastname: Souza
authors.forename: Gerald W
authors.initials: GW
authors.lastname: Zamponi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D015151:Immunoblotting; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary; D051381:Rats; D014162:Transfection
chemical_list: C504728:Cacna1c protein, rat; D020746:Calcium Channels, L-Type; D002147:Calmodulin; D002118:Calcium