Crystal structures of wild type and disease mutant forms of the ryanodine receptor SPRY2 domain

Ryanodine receptors (RyRs) form channels responsible for the release of Ca2+ from the endoplasmic and sarcoplasmic reticulum. The SPRY2 domain in the skeletal muscle isoform (RyR1) has been proposed as a direct link with L-type calcium channels (Ca(V)1.1), allowing for direct mechanical coupling between plasma membrane depolarization and Ca2+ release. Here we present the crystal structures of the SPRY2 domain from RyR1 and RyR2 at 1.34-1.84 angstrom resolution. They form two antiparallel beta sheets establishing a core, and four additional modules of which several are required for proper folding. A buried disease mutation, linked to hypertrophic cardiomyopathy and loss-of-function, induces local misfolding and strong destabilization. Isothermal titration calorimetry experiments negate the RyR1 SPRY2 domain as the major link with Ca(V)1.1. Instead, docking into full-length RyR1 cryo-electron microscopy maps suggests that the SPRY2 domain forms a link between the N-terminal gating ring and the clamp region.