The General Anaesthetic Binding Site of Calmodulin Disrupts Ryanodine Peptide Binding

Abstract

The skeletal muscle Ryanodine Receptor (RyR1) is a large calcium release channel involved in excitation-contraction coupling. It is also the target for hundreds of disease mutations that cause malignant hyperthermia (MH) or skeletal muscle disorders like central core disease (CCD). MH is typically triggered by volatile anesthetics, but their binding site on RyR1 has not been fully described. RyR1 is under the control of several auxiliary proteins. One of these is Calmodulin (CaM), a Ca2+-binding protein that can suppress RyR1 activity at elevated Ca2+ concentrations. Here we investigate how CaM can bind to RyR1, and how this may be affected by volatile anesthetics. We found that CaM can bind to at least three different RyR1 peptides, with the affinity and lobe specificity being altered substantially by the Ca2+ concentrations. In addition, we identified two binding sites for sevoflurane, a volatile anesthetic, on Ca2+/CaM. The anesthetic binds to a pocket that is involved in binding RyR1 peptides. In addition, it can alter the affinity of the N-terminal CaM lobe for Ca2+. These findings suggest that binding of anesthetics to CaM may be involved in the pathophysiology of malignant hyperthermia.