title: Crystallographic basis for calcium regulation of sodium channels.
abstract: Voltage-gated sodium channels underlie the rapid regenerative upstroke of action potentials and are modulated by cytoplasmic calcium ions through a poorly understood mechanism. We describe the 1.35 Å crystal structure of Ca(2+)-bound calmodulin (Ca(2+)/CaM) in complex with the inactivation gate (DIII-IV linker) of the cardiac sodium channel (Na(V)1.5). The complex harbors the positions of five disease mutations involved with long Q-T type 3 and Brugada syndromes. In conjunction with isothermal titration calorimetry, we identify unique inactivation-gate mutations that enhance or diminish Ca(2+)/CaM binding, which, in turn, sensitize or abolish Ca(2+) regulation of full-length channels in electrophysiological experiments. Additional biochemical experiments support a model whereby a single Ca(2+)/CaM bridges the C-terminal IQ motif to the DIII-IV linker via individual N and C lobes, respectively. The data suggest that Ca(2+)/CaM destabilizes binding of the inactivation gate to its receptor, thus biasing inactivation toward more depolarized potentials.
authors.affiliation: Department of Anesthesiology, Pharmacology and Therapeutics, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada, V6T 1Z3.
authors.forename: Maen F
authors.initials: MF
authors.lastname: Sarhan
authors.forename: Ching-Chieh
authors.initials: CC
authors.lastname: Tung
authors.forename: Filip
authors.initials: F
authors.lastname: Van Petegem
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Ahern
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D053840:Brugada Syndrome / Q000235:genetics; D002118:Calcium / Q000737:chemistry / Q000502:physiology*; D002147:Calmodulin / Q000737:chemistry* / Q000502:physiology; D018360:Crystallography, X-Ray; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008133:Long QT Syndrome / Q000235:genetics; D046911:Macromolecular Substances; D008564:Membrane Potentials; D008958:Models, Molecular; D008969:Molecular Sequence Data; D062554:NAV1.5 Voltage-Gated Sodium Channel; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry* / Q000502:physiology
chemical_list: C488659:CALM2 protein, human; D002147:Calmodulin; D046911:Macromolecular Substances; D062554:NAV1.5 Voltage-Gated Sodium Channel; D011993:Recombinant Fusion Proteins; C568320:SCN5A protein, human; D015222:Sodium Channels; D012964:Sodium; D002118:Calcium