title: Pore dynamics and conductance of RyR1 transmembrane domain.
abstract: Ryanodine receptors (RyR) are calcium release channels, playing a major role in the regulation of muscular contraction. Mutations in skeletal muscle RyR (RyR1) are associated with congenital diseases such as malignant hyperthermia and central core disease (CCD). The absence of high-resolution structures of RyR1 has limited our understanding of channel function and disease mechanisms at the molecular level. Previously, we have reported a hypothetical structure of the RyR1 pore-forming region, obtained by homology modeling and supported by mutational scans, electrophysiological measurements, and cryo-electron microscopy. Here, we utilize the expanded model encompassing six transmembrane helices to calculate the RyR1 pore region conductance, to analyze its structural stability, and to hypothesize the mechanism of the Ile4897 CCD-associated mutation. The calculated conductance of the wild-type RyR1 suggests that the proposed pore structure can sustain ion currents measured in single-channel experiments. We observe a stable pore structure on timescales of 0.2 μs, with multiple cations occupying the selectivity filter and cytosolic vestibule, but not the inner chamber. We further suggest that stability of the selectivity filter critically depends on the interactions between the I4897 residue and several hydrophobic residues of the neighboring subunit. Loss of these interactions in the case of polar substitution I4897T results in destabilization of the selectivity filter, a possible cause of the CCD-specific reduced Ca(2+) conductance.
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: David
authors.initials: D
authors.lastname: Shirvanyants
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Ramachandran
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: Yingwu
authors.initials: Y
authors.lastname: Mei
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: Le
authors.initials: L
authors.lastname: Xu
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina. Electronic address: meissner@med.unc.edu.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Meissner
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina, Chapel Hill, North Carolina. Electronic address: dokh@unc.edu.
authors.forename: Nikolay V
authors.initials: NV
authors.lastname: Dokholyan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015640:Ion Channel Gating; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium