A chemigenetic indicator based on a synthetic chelator and a green fluorescent protein for imaging of intracellular sodium ions†

Abstract

A chemigenetic indicator with an affinity suitable for imaging of intracellular sodium ions (Na⁺) in mammalian cells was developed. The indicator, based on a chimera of green fluorescent protein (GFP) and HaloTag labeled with a synthetic crown ether chelator, was produced by a combination of rational design and directed evolution. In mammalian cells the indicator exhibited an approximately 100% increase in excitation ratio when the cells were treated with 20 mM Na⁺ and an ionophore.