Imaging of intracellular free Zn ²⁺ in real time using genetically-encoded FRET sensors

Abstract

Whilst Zn ²⁺ ions are critical regulators of many fundamental cellular processes, methods to monitor the free concentrations of these ions dynamically within living cells are presently limited. We have developed a series of genetically-encoded Förster Resonance Energy Transfer (FRET)-based sensors that display a large ratiometric change upon Zn ²⁺ binding, have affinities that span the pico- to nanomolar range, and can readily be targeted to subcellular organelles. These sensors reveal that the free cytosolic Zn ²⁺ concentration of fibroblasts and pancreatic islet β-cells is tightly buffered at ~400 pM, a level at least 10 ³-fold lower than that in secretory granules.