Crystallized structure of rabbit ryanodine receptor (RyR)1 for amino acid residues 1-559. This RyR1 segment folds into three distinct domains, forming a vestibule around the four-fold symmetry axis: domain A (blue; 1-205), domain B (green; 206-394) and domain C (red; 395-532). (A) Cytoplasmic view; (B) close-up lateral view from the four-fold symmetry axis, (C) Docking of domain A alone (blue) or domain BC alone (red) yields a near-perfect superposition on the docking position for ABC (grey). Adapted from Tung, et al. .