Fig. 1. Mutations to the V220 position in the S4 transmembrane helix affects the voltage range of the GEVI. A. Comparison of the V220R and V220T mutants. The protein sequence of the S4 transmembrane helix of CC1 shows the classic RXXR motif. The schematic of the GEVI, CC1 with the voltage-sensing domain in the plasma membrane and the fluorescent protein, super ecliptic pHlorin with the A227D mutation depicted in green in the cytoplasm. Positively charged residues are red. Optical traces are from whole-cell clamped HEK 293 cells expressing CC1 (black), V220R (blue), or V220T (red) subjected to a series of voltage steps. The dark lines are the average of at least 4 cells. Shaded area is the standard error of the mean. Right graph is a Boltzman plot of the normalized fluorescence change. The V220R mutant does not have enough data points for a reliable fit. B. Representative examples of mutations to the V220 position. See table one for complete list. Command voltage pulses are depicted in black.
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