title: The proximal C-terminus of α(1C) subunits is necessary for junctional membrane targeting of cardiac L-type calcium channels.
abstract: In cardiac myocytes, LTCCs (L-type calcium channels) form a functional signalling complex with ryanodine receptors at the JM (junctional membrane). Although the specific localization of LTCCs to the JM is critical for excitation-contraction coupling, their targeting mechanism is unclear. Transient transfection of GFP (green fluorescent protein)-α(1S) or GFP-α(1C), but not P/Q-type calcium channel α(1A), in dysgenic (α(1S)-null) GLT myotubes results in correct targeting of these LTCCs to the JMs and restoration of action-potential-induced Ca2+ transients. To identify the sequences of α(1C) responsible for JM targeting, we generated a range of α(1C)-α(1A) chimaeras, deletion mutants and alanine substitution mutants and studied their targeting properties in GLT myotubes. The results revealed that amino acids L(1681)QAGLRTL(1688) and P(1693)EIRRAIS(1700), predicted to form two adjacent α-helices in the proximal C-terminus, are necessary for the JM targeting of α(1C). The efficiency of restoration of action-potential-induced Ca2+ transients in GLT myotubes was significantly decreased by mutations in the targeting motif. JM targeting was not disrupted by the distal C-terminus of α(1C) which binds to the second α-helix. Therefore we have identified a new structural motif in the C-terminus of α(1C) that mediates the targeting of cardiac LTCCs to JMs independently of the interaction between proximal and distal C-termini of α(1C).
authors.affiliation: Department of Molecular Pharmacology, Shinshu University School of Medicine, Matsumoto, Nagano, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Nakada
authors.forename: Bernhard E
authors.initials: BE
authors.lastname: Flucher
authors.forename: Toshihide
authors.initials: T
authors.lastname: Kashihara
authors.forename: Xiaona
authors.initials: X
authors.lastname: Sheng
authors.forename: Toshihide
authors.initials: T
authors.lastname: Shibazaki
authors.forename: Miwa
authors.initials: M
authors.lastname: Horiuchi-Hirose
authors.forename: Simmon
authors.initials: S
authors.lastname: Gomi
authors.forename: Masamichi
authors.initials: M
authors.lastname: Hirose
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Yamada
mesh_terms: D000200:Action Potentials; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D020746:Calcium Channels, L-Type / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D016296:Mutagenesis; D032383:Myocytes, Cardiac / Q000378:metabolism; D017433:Protein Structure, Secondary; D021122:Protein Subunits; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; C419385:L-type calcium channel alpha(1C); D021122:Protein Subunits; D011993:Recombinant Fusion Proteins