Figure 1: Proposed mechanism of voltage-dependent fluorescence in eFRET GEVIs.
From: Bright and fast multicoloured voltage reporters via electrochromic FRET
Voltage controls the protonation, and thereby the absorption spectrum, of the Schiff base joining the retinal to the protein scaffold. (a) At a depolarizing (positive) voltage, the microbial rhodopsin has a protonated retinal Schiff base, which absorbs strongly with a peak near 600 nm. The retinal absorption quenches the fluorescence of the appended fluorescent protein (FP). (b) At hyperpolarizing (negative) voltages, the fluorescence is not quenched. Spectra shown are cartoons to illustrate mechanism.
