Fig. 1.

Homo-FRET Ca²⁺ indicator, W-Cameleon. (a) Normalized absorption and emission spectra of YFP and the overlap integral. (b) Schematic sequence of W-Cameleon. (c) Conformational change of W-Cameleon, with and without Ca²⁺. CaM-M13 is unpacked in the absence of Ca²⁺, but FRET, which would cause depolarization of Venus, occurs. In contrast, CaM-M13 is packed, but there is no FRET. (d) Titration curve of the fluorescence anisotropy change of W-Cameleon, upon Ca²⁺ binding. Plots were fitted by Hill's equation.