Crystal Structure of Cardiac Ryanodine Receptor N-Terminal Region Contains Unique Anion Binding Site Targeted by Disease-Associated Mutations

Abstract

Ryanodine receptors (RyRs) are intracellular calcium-release channels of the endo/sarcoplasmic reticulum that are critical to the muscle excitation-contraction coupling. Mutations in the cardiac isoform (RyR2) are linked to life-threatening arrhythmias, such as catecholaminergic polymorphic ventricular tachycardia (CPVT), known for a sudden cardiac arrest. RyR2 is the target for over 150 disease-associated mutations. Here, we present the 2.0A crystal structure of the N-terminal region of RyR2 (residues 1-547), an area containing 29 distinct disease-associated mutations. The protein folds up in three individual domains similarly to its counterpart in the skeletal muscle, RyR1, but contains a unique central chloride anion that holds together the three domains. The CPVT-associated mutant R420Q targets one of the Arginines coordinating the anion and ablates chloride binding. The crystal structure of the mutant shows reorientations in the first two domains relative to the third, likely destabilizing intersubunit interactions in the context of an intact channel. Chloride anion binding may represent one of the ways RyR2 uses to regulate channel opening.