title: The recombinant dihydropyridine receptor II-III loop and partly structured 'C' region peptides modify cardiac ryanodine receptor activity.
abstract: A physical association between the II-III loop of the DHPR (dihydropryidine receptor) and the RyR (ryanodine receptor) is essential for excitation-contraction coupling in skeletal, but not cardiac, muscle. However, peptides corresponding to a part of the II-III loop interact with the cardiac RyR2 suggesting the possibility of a physical coupling between the proteins. Whether the full II-III loop and its functionally important 'C' region (cardiac DHPR residues 855-891 or skeletal 724-760) interact with cardiac RyR2 is not known and is examined in the present study. Both the cardiac DHPR II-III loop (CDCL) and cardiac peptide (C(c)) activated RyR2 channels at concentrations >10 nM. The skeletal DHPR II-III loop (SDCL) activated channels at < or =100 nM and weakly inhibited at > or =1 microM. In contrast, skeletal peptide (C(s)) inhibited channels at all concentrations when added alone, or was ineffective if added in the presence of C(c). Ca2+-induced Ca2+ release from cardiac sarcoplasmic reticulum was enhanced by CDCL, SDCL and the C peptides. The results indicate that the interaction between the II-III loop and RyR2 depends critically on the 'A' region (skeletal DHPR residues 671-690 or cardiac 793-812) and also involves the C region. Structure analysis indicated that (i) both C(s) and C(c) are random coil at room temperature, but, at 5 degrees C, have partial helical regions in their N-terminal and central parts, and (ii) secondary-structure profiles for CDCL and SDCL are similar. The data provide novel evidence that the DHPR II-III loop and its C region interact with cardiac RyR2, and that the ability to interact is not isoform-specific.
authors.affiliation: Division of Molecular Bioscience, John Curtin School of Medical Research, Australian National University, PO Box 334, Canberra, ACT 2601, Australia. angela.dulhunty@anu.edu.au
authors.forename: Angela F
authors.initials: AF
authors.lastname: Dulhunty
authors.forename: Yamuna
authors.initials: Y
authors.lastname: Karunasekara
authors.forename: Suzanne M
authors.initials: SM
authors.lastname: Curtis
authors.forename: Peta J
authors.initials: PJ
authors.lastname: Harvey
authors.forename: Philip G
authors.initials: PG
authors.lastname: Board
authors.forename: Marco G
authors.initials: MG
authors.lastname: Casarotto
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D003593:Cytoplasm / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects*; D009682:Magnetic Resonance Spectroscopy; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012996:Solutions; D013696:Temperature
chemical_list: D020746:Calcium Channels, L-Type; D010446:Peptide Fragments; D020033:Protein Isoforms; D011994:Recombinant Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D012996:Solutions; D000255:Adenosine Triphosphate; D002118:Calcium