UBC Theses and Dissertations
Structural and biochemical characterizations of the skeletal muscle and cardiac ryanodine receptor N-terminal disease-associated mutants Kimlicka, Lynn
Ryanodine receptors (RyRs) are calcium release channels located in the endo/sarcoplasmic reticulum that play a crucial role in the excitation-contraction coupling. Over 500 mutations have been found in the skeletal muscle (RyR1) and cardiac (RyR2) isoforms that cause severe muscle disorders or life-threatening arrhythmias. Mechanisms of these mutations have remained elusive largely due to the lack of high-resolution structures. Here, we compare pseudo-atomic models of the N-terminal region of RyR1 in the open and closed states together with crystal structures and thermal melts of multiple disease-associated mutants. We describe a model in which the intersubunit interface at the N-terminal region acts as a brake in channel opening. Next, we depict crystal structures of mutants at the intersubunit interface of RyR2 N-terminal region that perturb the structure of a loop targeted by multiple mutations. Furthermore, the crystal structure of the N-terminal domains of RyR2 reveals a unique, central anion-binding site. This anion binding is ablated in a disease-associated mutant that targets one of the anion-coordinating arginine residues, resulting in domain reorientations. Several other disease-causing mutations destabilize the protein. Taken together, the results illustrate a common theme across the RyR isoforms and their homologous IP₃ receptors that conformational changes at the N-terminal region caused by the destabilization of the interfaces are allosterically coupled to channel opening.
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