title: Cryo-electron microscopy and three-dimensional reconstruction of the calcium release channel/ryanodine receptor from skeletal muscle.
abstract: The calcium release channel (CRC) from skeletal muscle is an unusually large tetrameric ion channel of the sarcoplasmic reticulum, and it is a major component of the triad junction, the site of excitation contraction coupling. The three-dimensional architecture of the CRC was determined from a random conical tilt series of images extracted from electron micrographs of isolated detergent-solubilized channels prepared in a frozen-hydrated state. Three major classes of fourfold symmetric images were identified, and three-dimensional reconstructions were determined for two of these. The two independent reconstructions were almost identical, being related to each other by a 180 degrees rotation about an axis in the plane of the specimen grid. The CRC consists of a large cytoplasmic assembly (29 x 29 x 12 nm) and a smaller transmembrane assembly that protrudes 7 nm from one of its faces. A cylindrical low-density region, 2-3 nm in apparent diameter, extends down the center of the transmembrane assembly, and possibly corresponds to the transmembrane Ca(2+)-conducting pathway. At its cytoplasmic end this channel-like feature appears to be plugged by a globular mass of density. The cytoplasmic assembly is apparently constructed from 10 or more domains that are loosely packed together such that greater than 50% of the volume enveloped by the assembly is occupied by solvent. The cytoplasmic assembly is suggestive of a scaffolding and seems well adapted to maintain the structural integrity of the triad junction while allowing ions to freely diffuse to and away from the transmembrane assembly.
authors.affiliation: Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany 12201-0509.
authors.forename: M
authors.initials: M
authors.lastname: Radermacher
authors.forename: V
authors.initials: V
authors.lastname: Rao
authors.forename: R
authors.initials: R
authors.lastname: Grassucci
authors.forename: J
authors.initials: J
authors.lastname: Frank
authors.forename: A P
authors.initials: AP
authors.lastname: Timerman
authors.forename: S
authors.initials: S
authors.lastname: Fleischer
authors.forename: T
authors.initials: T
authors.lastname: Wagenknecht
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000648:ultrastructure*; D003593:Cytoplasm; D005615:Freezing; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D008958:Models, Molecular; D009124:Muscle Proteins / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000648:ultrastructure; D011487:Protein Conformation; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum
chemical_list: D015220:Calcium Channels; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel