29.06.2021 | Webinar: Channelopathies resolved via cryo-EM and X-ray crystallography: an investigation of muscle excitation-contraction coupling
Orbit mini Webinar
Date: June 29. 2021, 5:00 PM CEST (8:00 AM PDT)
Dr. Conrad Weichbrodt (Senior Scientist / Product Manager Orbit family; Nanion Technologies)
Dr. Filip Van Petegem (Professor, Biochemistry and Molecular Biology - University of British Columbia)
Muscle contraction requires a tight communication between Ca2+-permeable ion channels located in the plasma membrane (L-type calcium channels, CaVs ) and in the Sarcoplasmic Reticulum (Ryanodine Receptors, RyRs). In cardiac muscle, Ca2+ entering through CaV1.2 can stimulate the nearby RyR2 isoform, through a process of Ca2+-induced Ca2+ release. In skeletal muscle, however, the coupling is thought to occur mechanically, with voltage-dependent conformational changes in CaV1.1 being transmitted to RyR1, either through direct or indirect interactions. Mutations in RyR1 (as well as CaV1.1) can give rise to malignant hyperthermia (MH), a potentially lethal condition typically triggered by volatile anaesthetics. Other mutations cause central core disease (CCD), whereas some are linked to both MH and CCD. Similarly, mutations in RyR2 are linked to a form of stress-induced cardiac arrhythmia, known as CPVT (catecholaminergic polymorphic ventricular tachycardia). Our lab has been solving crystal structures of isolated RyR domains in WT and disease mutant forms, which show that many mutations cause conformational changes. More recently, we solved cryo-EM structures of RyR1 carrying the founding mutation (R615C) that links RyR1 to malignant hyperthermia. The structures show how many mutations can destabilize the closed state, leading to facilitated channel opening.
In addition, RyRs are heavily regulated by kinases (PKA, CaMKII) that can also facilitate channel opening. Excessive phosphorylation of RyRs has been linked to a range of acquired disorders, including atrial fibrillation and arrhythmias during heart failure. We elucidated how PKA recognizes the cardiac RyR2 via an unusual interface and show that phosphorylation may induce the formation of extra secondary structure elements.
Finally, I will discuss our efforts to understand the mechanical coupling between CaV1.1 and RyR1 in skeletal muscle. STAC3 is a small protein recently shown to be essential for the coupling. We found this protein to interact with a cytosolic loop of CaV1.1 and found that several mutations in STAC3, linked to myopathy, directly affect this interaction and the mechanical coupling.