Design and characterization of a DNA‐encoded, voltage‐sensitive fluorescent protein

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Abstract
Optical imaging of electrical activity has been suggested as a promising approach to investigate the multineuronal representation of information processing in brain tissue. While considerable progress has been made in the development of instrumentation suitable for high‐speed imaging, intrinsic or extrinsic dye‐mediated optical signals are often of limited use due to their slow response dynamics, low effective sensitivity, toxicity or undefined cellular origin. Protein‐based and DNA‐encoded voltage sensors could overcome these limitations. Here we report the design and generation of a voltage‐sensitive fluorescent protein (VSFP) consisting of a voltage sensing domain of a potassium channel and a pair of cyan and yellow emitting mutants of green fluorescent protein (GFP). In response to a change in transmembrane voltage, the voltage sensor alters the amount of fluorescence resonance energy transfer (FRET) between the pair of GFP mutants. The optical signals respond in the millisecond time‐scale of fast electrical signalling and are large enough to allow monitoring of voltage changes at the single cell level.