[Frontiers in Bioscience 7, d1464-1474, June 1, 2002]


Terence Wagenknecht1,2 and Montserrat Samsó 1

1Biggs Laboratory, Wadsworth Center, New York State Department of Health, Albany, NY 12201, 2Department of Biomedical Sciences School of Public Health, State University of New York at Albany, Albany, NY 12201


1. Abstract
2. Introduction
3. Basic Features of RyR Architecture
3.1. Cytoplasmic Assembly/Region
3.2. Transmembrane assembly/region
4. Comparison of RyR Isoforms
5. Conformational States or RyR1 and RyR3
6. Interaction Sites of RyR Modulators
6.1. FKBP12
6.2. Calmodulin
6.3. Dihydropyridine Receptor
7. Correlation of RyR1's amino acid sequence with its 3D architecture
8. Perspective
8.1. High resolution
8.2. 3D localization of functional/structural sites
9. Acknowledgment
10. References


Nearly all available information on the three-dimensional structure of the ryanodine receptor (RyR) class of intracellular calcium release channels has come from electron microscopy. This review focuses on results that have been obtained by cryo-electron microscopy of purified, detergent-solubilized receptors in combination with single-particle image processing. This approach has led to the most detailed 3D models of RyRs, which are currently at resolutions of 20-30 Å. All three of the known genetic isoforms show essentially identical architectures at this resolution: a large, 4-fold symmetric, cytoplasmic assembly that accounts for greater than 80% of the receptor's mass and is composed of at least 10 discrete, loosely packed domains, and a transmembrane region whose dimensions lead us to conclude that very little of RyR's protein mass is present on the lumenal side of the sarco/endoplasmic reticulum. Three-dimensional reconstructions determined for RyRs that have been exposed to conditions that promote either open or closed states show subtle differences, some of which are located in the cytoplasmic assembly, at sites more distant than 100 Å from the ion channel in the transmembrane region. Several of the ligands (FK506-binding protein, calmodulin, dihydropyridine receptor) that interact in vivo with the skeletal RyR have been, or are in the process of being, mapped to various locations on the cytoplasmic assembly.