Fig. 7: Model for the rsEGFP2 off-to-on photoswitching process.
The bold purple bar represents the laser_on_∆10 ns intermediate structure determined by TR-SFX. Time constants correspond to those determined by femtosecond (87 ps) and nanosecond-resolved pump–probe UV–visible absorption spectroscopy (5.57, 36.1 and 825 µs) in H2O solution (50 mM HEPES pH 8, 50 mM NaCl). All three cis protonated states (purple bars) are ground-state intermediates, interconversion of which involves rearrangements of the protein matrix (orange arrows). Corresponding structural models for the chromophore and His149 as determined by X-ray crystallography are shown in panels a, b (this work) and d27. Trans1 and His149-off (light gray) and trans2 and His149-supp (dark gray) of the trans-protonated off-state (a, Fig. 3c) transited to cis and His149-off-like at 10 ns (b, Fig. 4b, Fig. 6b, e). His149-off-like has moved to His149-on in the cis anionic on state (d, Fig. 6c, f). The structure whose intermediate forms in 5.57 µs remains elusive (c).
