Mg2+ plays important roles in many physiological processes. However, the underlying molecular mechanisms, especially in the apoptotic pathway, remain unclear due to the diffusion of Mg2+ probes, which hinders long-term imaging in specific organelles. We developed an immobilized Mg2+ probe, MGH, which is covalently conjugated with the HaloTag protein in various organelles. HaloTag-coupled MGH enabled long-term imaging of intracellular local Mg2+ dynamics for 24 h. To exploit this remarkable property, MGH was applied to the investigation of intracellular Mg2+ dynamics during apoptosis. Time-lapse imaging revealed an increase in the Mg2+ concentration after apoptotic cell shrinkage. Combined imaging analyses of intracellular Mg2+ and ATP concentrations strongly suggested that this Mg2+ concentration increase was caused by the dissociation of Mg2+ from ATP, along with a decrease in the intracellular ATP concentration. Thus, this protein-coupled Mg2+ probe could be a new chemical tool to elucidate intracellular Mg2+ dynamics with high spatiotemporal resolution.
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