Abstract
S100A1, a calcium-binding protein, plays a crucial role in regulating Ca(2+) signaling pathways in skeletal and cardiac myocytes via interactions with the ryanodine receptor (RyR) to affect Ca(2+) release and contractile performance. Biophysical studies strongly suggest that S100A1 interacts with RyRs but have been inconclusive about both the nature of this interaction and its competition with another important calcium-binding protein, calmodulin (CaM). Thus, high-resolution cryo-EM studies of RyRs in the presence of S100A1, with or without additional CaM, were needed. The elegant work by Weninger et al. demonstrates the interaction between S100A1 and RyR1 through various experiments and confirms that S100A1 activates RyR1 at sub-micromolar Ca(2+) concentrations, increasing the open probability of RyR1 channels.