title: The three-dimensional structure of the cardiac L-type voltage-gated calcium channel: comparison with the skeletal muscle form reveals a common architectural motif.
abstract: We describe here the first three-dimensional structure of the cardiac L-type voltage-gated calcium channel (VGCC) purified from bovine heart. The structure was determined by electron microscopy and single particle analysis of negatively stained complexes, using the angular reconstitution method. The cardiac VGCC can be isolated as a stable dimer, as reported previously for the skeletal muscle VGCC, with a central aqueous chamber formed by the two halves of the complex. Moreover, we demonstrate that the dimeric cardiac VGCC binds the dihydropyridine [3H]azidopine with a Kd approximately 310 pM. We have compared the cardiac VGCC structure with the skeletal muscle form, determined using the same reconstructive methodology, allowing us to identify common and distinct features of the complexes. By using antibody and lectin-gold labeling, we have localized the intracellular beta polypeptides and the extracellular glycosylation sites of the skeletal muscle VGCC, which can be correlated to the cardiac three-dimensional structure. From the data presented here the assignment of the orientation of the VGCC complexes with respect to the lipid bilayer is now possible. A difference between the cardiac and skeletal muscle ion channels is apparent in the putative transmembrane region, which would be consistent with the absence of the gamma subunit in the cardiac VGCC assembly.
authors.affiliation: Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, UK.
authors.forename: Ming-Chuan
authors.initials: MC
authors.lastname: Wang
authors.forename: Richard F
authors.initials: RF
authors.lastname: Collins
authors.forename: Robert C
authors.initials: RC
authors.lastname: Ford
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Berrow
authors.forename: Annette C
authors.initials: AC
authors.lastname: Dolphin
authors.forename: Ashraf
authors.initials: A
authors.lastname: Kitmitto
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D020746:Calcium Channels, L-Type / Q000737:chemistry*; D002417:Cattle; D002845:Chromatography; D019281:Dimerization; D006031:Glycosylation; D007091:Image Processing, Computer-Assisted; D015151:Immunoblotting; D007700:Kinetics; D037102:Lectins / Q000737:chemistry; D008854:Microscopy, Electron; D008954:Models, Biological; D008982:Molybdenum / Q000737:chemistry; D018482:Muscle, Skeletal / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014199:Trehalose / Q000737:chemistry
chemical_list: D020746:Calcium Channels, L-Type; D037102:Lectins; D008982:Molybdenum; D014199:Trehalose; C022175:ammonium molybdate