Investigating dual Ca 2+ modulation of the ryanodine receptor 1 by molecular dynamics simulation

The ryanodine receptors (RyR) are essential to calcium signaling in striated muscles. A deep understanding of the complex Ca 2+ ‐activation/inhibition mechanism of RyRs requires detailed structural and dynamic information for RyRs in different functional states (eg, with Ca 2+ bound to activating or inhibitory sites). Recently, high‐resolution structures of the RyR isoform 1 (RyR1) were solved by cryo‐electron microscopy, revealing the location of a Ca 2+ binding site for activation. Toward elucidating the Ca 2+ ‐modulation mechanism of RyR1, we performed extensive molecular dynamics simulation of the core RyR1 structure in the presence and absence of activating and solvent Ca 2+ (total simulation time is >5 μs). In the presence of solvent Ca 2+ , Ca 2+ binding to the activating site enhanced dynamics of RyR1 with higher inter‐subunit flexibility, asymmetric inter‐subunit motions, outward domain motions and partial pore dilation, which may prime RyR1 for subsequent channel opening. In contrast, the solvent Ca 2+ alone reduced dynamics of RyR1 and led to inward domain motions and pore contraction, which may cause inhibition. Combining our simulation with the map of disease mutation sites in RyR1, we constructed a wiring diagram of key domains coupled via specific hydrogen bonds involving the mutation sites, some of which were modulated by Ca 2+ binding. The structural and dynamic information gained from this study will inform future mutational and functional studies of RyR1 activation and inhibition by Ca 2+ .