title: An α-helical C-terminal tail segment of the skeletal L-type Ca2+ channel β1a subunit activates ryanodine receptor type 1 via a hydrophobic surface.
abstract: Excitation-contraction (EC) coupling in skeletal muscle depends on protein interactions between the transverse tubule dihydropyridine receptor (DHPR) voltage sensor and intracellular ryanodine receptor (RyR1) calcium release channel. We present novel data showing that the C-terminal 35 residues of the β(1a) subunit adopt a nascent α-helix in which 3 hydrophobic residues align to form a hydrophobic surface that binds to RyR1 isolated from rabbit skeletal muscle. Mutation of the hydrophobic residues (L496, L500, W503) in peptide β(1a)V490-M524, corresponding to the C-terminal 35 residues of β(1a), reduced peptide binding to RyR1 to 15.2 ± 7.1% and prevented the 2.9 ± 0.2-fold activation of RyR1 by 10 nM wild-type peptide. An upstream hydrophobic heptad repeat implicated in β(1a) binding to RyR1 does not contribute to RyR1 activation. Wild-type β(1a)A474-A508 peptide (10 nM), containing heptad repeat and hydrophobic surface residues, increased RyR1 activity by 2.3 ± 0.2- and 2.2 ± 0.3-fold after mutation of the heptad repeat residues. We conclude that specific hydrophobic surface residues in the 35 residue β(1a) C-terminus bind to RyR1 and increase channel activity in lipid bilayers and thus may support skeletal EC coupling.
authors.affiliation: Department of Translational Bioscience, John Curtin School of Medical Research, Australian National University, P.O. Box 334, Canberra, ACT 2601, Australia.
authors.forename: Yamuna
authors.initials: Y
authors.lastname: Karunasekara
authors.forename: Robyn T
authors.initials: RT
authors.lastname: Rebbeck
authors.forename: Llara M
authors.initials: LM
authors.lastname: Weaver
authors.forename: Philip G
authors.initials: PG
authors.lastname: Board
authors.forename: Angela F
authors.initials: AF
authors.lastname: Dulhunty
authors.forename: Marco G
authors.initials: MG
authors.lastname: Casarotto
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D020746:Calcium Channels, L-Type / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D056966:Excitation Contraction Coupling; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013499:Surface Properties
chemical_list: D000596:Amino Acids; C492923:Cacnb1 protein, mouse; D020746:Calcium Channels, L-Type; D019837:Ryanodine Receptor Calcium Release Channel