New Sensors for Quantitative Measurement of Mitochondrial Zn2+

Zinc (Zn2+) homeostasis plays a vital role in cell function, and the dysregulation of intracellular Zn2+ is associated with mitochondria] dysfunction. Few tools exist to quantitatively monitor the buffered, free Zn2+ concentration in mitochondria of living cells ([Zn2+](mito)). We have validated three high dynamic range, ratiometric, genetically encoded, fluorescent Zn2+ sensors that we have successfully used to precisely measure and monitor [Zn2+](mito) in several cell types. Using one of these sensors, called mito-ZapCY1, we report observations that free Zn2+ is buffered at concentrations about 3 orders of magnitude lower in mitochondria than in the cytosol and that HeLa cells expressing mito-ZapCY1 have an average [Zn2+](mito) of 0.14 pM, which differs significantly from other cell types. These optimized mitochondrial Zn2+ sensors could improve our understanding of the relationship between Zn2+ homeostasis and mitochondrial function.