title: Structural insights into activation of the retinal L-type Ca²⁺ channel (Cav1.4) by Ca²⁺-binding protein 4 (CaBP4).
abstract: CaBP4 modulates Ca(2+)-dependent activity of L-type voltage-gated Ca(2+) channels (Cav1.4) in retinal photoreceptor cells. Mg(2+) binds to the first and third EF-hands (EF1 and EF3), and Ca(2+) binds to EF1, EF3, and EF4 of CaBP4. Here we present NMR structures of CaBP4 in both Mg(2+)-bound and Ca(2+)-bound states and model the CaBP4 structural interaction with Cav1.4. CaBP4 contains an unstructured N-terminal region (residues 1-99) and four EF-hands in two separate lobes. The N-lobe consists of EF1 and EF2 in a closed conformation with either Mg(2+) or Ca(2+) bound at EF1. The C-lobe binds Ca(2+) at EF3 and EF4 and exhibits a Ca(2+)-induced closed-to-open transition like that of calmodulin. Exposed residues in Ca(2+)-bound CaBP4 (Phe(137), Glu(168), Leu(207), Phe(214), Met(251), Phe(264), and Leu(268)) make contacts with the IQ motif in Cav1.4, and the Cav1.4 mutant Y1595E strongly impairs binding to CaBP4. We conclude that CaBP4 forms a collapsed structure around the IQ motif in Cav1.4 that we suggest may promote channel activation by disrupting an interaction between IQ and the inhibitor of Ca(2+)-dependent inactivation domain.
authors.affiliation: From the Department of Chemistry, University of California, Davis, California 95616.
authors.forename: Saebomi
authors.initials: S
authors.lastname: Park
authors.affiliation: From the Department of Chemistry, University of California, Davis, California 95616.
authors.forename: Congmin
authors.initials: C
authors.lastname: Li
authors.affiliation: the Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195, and.
authors.forename: Françoise
authors.initials: F
authors.lastname: Haeseleer
authors.affiliation: the Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Palczewski
authors.affiliation: From the Department of Chemistry, University of California, Davis, California 95616, jbames@ucdavis.edu.
authors.forename: James B
authors.initials: JB
authors.lastname: Ames
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D002151:Calorimetry; D006801:Humans; D008274:Magnesium / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: C514441:CABP4 protein, human; C113330:CACNA1F protein, human; C494133:Cabp4 protein, mouse; C480684:Cacna1f protein, mouse; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D008274:Magnesium; D002118:Calcium
keywords: Calcium; Calcium Channel; Calcium-binding Protein; Calmodulin (CaM); Calorimetry; Nuclear Magnetic Resonance (NMR); Photoreceptor; Phototransduction; Structural Biology