Molecular basis for gating and regulation of cardiac ryanodine receptor: underlying mechanisms for gain- and loss-of function mutations

Summary Cardiac ryanodine receptor (RyR2) is a large Ca2+ release channel in the sarcoplasmic reticulum and indispensable for excitation-contraction coupling in the heart. RyR2 is activated by Ca2+ and RyR2 mutations have been implicated in severe arrhythmogenic heart diseases. Yet, the structural basis underlying channel opening and how mutations affect the channel remain unknown. Here, we combined high-resolution structures determined by cryo-electron microscopy with quantitative functional analysis of channels carrying various mutations in specific residues. We demonstrated two fundamental mechanisms for channel regulation: interactions close to the channel pore stabilize the channel to prevent hyperactivity and a series of interactions in the surrounding regions is necessary for channel opening upon Ca2+ binding. Mutations at the residues involved in the former and the latter mechanisms cause gain-of-function and loss-of-function, respectively. Our results reveal gating mechanisms of the RyR2 channel and alterations by pathogenic mutations at the atomic level.