RyR1 is an intracellular Ca²⁺ channel important in excitable cells such as neurons and muscle fibers. Ca²⁺ activates it at low concentrations and inhibits it at high concentrations. Mg²⁺ is the main physiological RyR1 inhibitor, an effect that is overridden upon activation. Despite the significance of Mg²⁺-mediated inhibition, the molecular-level mechanisms remain unclear. In this work we determined two cryo-EM structures of RyR1 with Mg²⁺ up to 2.8 Å resolution, identifying multiple Mg²⁺ binding sites. Mg²⁺ inhibits at the known Ca²⁺ activating site and we propose that the EF hand domain is an inhibitory divalent cation sensor. Both divalent cations bind to ATP within a crevice, contributing to the precise transmission of allosteric changes within the enormous channel protein. Notably, Mg²⁺ inhibits RyR1 by interacting with the gating helices as validated by molecular dynamics. This structural insight enhances our understanding of how Mg²⁺ inhibition is overcome during excitation.

Dicoumarols and coumarin derivatives have shown a variety of pharmaceutical activities and have been found to be potent inhibitor for the NAD(P)H‐dependent flavoproteins. In this report, dicoumarol and its derivatives containing the substituted benzene ring at the methylenebis position were synthesized and evaluated for their antibacterial activity against gram‐positive bacteria: Staphylococcus aureus and Bacillus subtilis, and gram‐negative bacteria: Escherichia coli and Klebsiella sp. The results showed that the synthesized dicoumarols affect cell growth but are selective against gram‐positive over gram‐negative bacterial cells. However, for most derivatives, the substitution of steric bulky benzene group on the methylenebis position appears to decrease in the efficacy of antibacterial effect. This finding is roughly described by the predicted poorer docked structure of the derivatives to a homology model of S. aureus flavoprotein. 3D‐QSAR study highlighted structural features around the substituted benzene ring of dicoumarols as the antibacterial activity. CoMFA and CoMSIA contour maps support the idea that steric repulsion at the para position could diminish the antibacterial activity. The results of this study provide a better understanding of the molecular basis for the antibacterial activity of dicoumarols.