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. 2019 Feb 26;13:53. doi: 10.3389/fncel.2019.00053

FIGURE 1.

FIGURE 1

Cartoon showing the different GEVI designs. (A) The majority of type 1 GEVIs consist of a molecular fusion of an isolated VSD, derived from a voltage-sensitive phosphatase, and a single FP, or a FRET FP pair. In FRET constructs, the FPs may be fused in tandem or to either terminus of the VSD. CFP, cyan fluorescent protein; YFP, yellow fluorescent protein. (B) Type 2 GEVIs comprise standalone microbial opsins, which possess seven transmembrane helices (TH1–TH7), or opsin-FRET constructs, where the opsin may be fused to a fluorophore. Microbial opsins exhibit broad absorption spectra (500–700 nm) and serve to “quench” the fluorescence of the appended fluorophore, during voltage fluctuations.