title: Calmodulin regulation of Nav1.4 current: role of binding to the carboxyl terminus.
abstract: Calmodulin (CaM) regulates steady-state inactivation of sodium currents (Na(V)1.4) in skeletal muscle. Defects in Na current inactivation are associated with pathological muscle conditions such as myotonia and paralysis. The mechanisms of CaM modulation of expression and function of the Na channel are incompletely understood. A physical association between CaM and the intact C terminus of Na(V)1.4 has not previously been demonstrated. FRET reveals channel conformation-independent association of CaM with the C terminus of Na(V)1.4 (CT-Na(V)1.4) in mammalian cells. Mutation of the Na(V)1.4 CaM-binding IQ motif (Na(V)1.4(IQ/AA)) reduces cell surface expression of Na(V)1.4 channels and eliminates CaM modulation of gating. Truncations of the CT that include the IQ region abolish Na current. Na(V)1.4 channels with one CaM fused to the CT by variable length glycine linkers exhibit CaM modulation of gating only with linker lengths that allowed CaM to reach IQ region. Thus one CaM is sufficient to modulate Na current, and CaM acts as an ancillary subunit of Na(V)1.4 channels that binds to the CT in a conformation-independent fashion, modulating the voltage dependence of inactivation and facilitating trafficking to the surface membrane.
authors.affiliation: Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Subrata
authors.initials: S
authors.lastname: Biswas
authors.forename: Isabelle
authors.initials: I
authors.lastname: Deschênes
authors.forename: Deborah
authors.initials: D
authors.lastname: Disilvestre
authors.forename: Yanli
authors.initials: Y
authors.lastname: Tian
authors.forename: Victoria L
authors.initials: VL
authors.lastname: Halperin
authors.forename: Gordon F
authors.initials: GF
authors.lastname: Tomaselli
mesh_terms: D002147:Calmodulin / Q000378:metabolism*; D002460:Cell Line; D031541:Fluorescence Resonance Energy Transfer; D005786:Gene Expression Regulation; D006801:Humans; D009124:Muscle Proteins / Q000737:chemistry* / Q000378:metabolism*; D009154:Mutation; D062553:NAV1.4 Voltage-Gated Sodium Channel; D011485:Protein Binding; D011487:Protein Conformation; D015222:Sodium Channels / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D009124:Muscle Proteins; D062553:NAV1.4 Voltage-Gated Sodium Channel; C106251:SCN4A protein, human; D015222:Sodium Channels