Optically Guided Photoactivity: Coordinating Tautomerization, Photoisomerization, Inhomogeneity, and Reactive Intermediates within the RcaE Cyanobacteriochrome.
The RcaE cyanobacteriochrome uses a linear tetrapyrrole chromophore to sense the ratio of green and red light to enable the Fremyella diplosiphon cyanobacterium to control the expression of the photosynthetic infrastructure for efficient utilization of incident light. The femtosecond photodynamics of the embedded phycocyanobilin chromophore within RcaE were characterized with dispersed femtosecond pump-dump-probe spectroscopy, which resolved a complex interplay of excited-state proton transfer, photoisomerization, multilayered inhomogeneity, and reactive intermediates. These reactions were integrated within a central model that incorporated a rapid (200 fs) excited-state Le Châtelier redistribution between parallel evolving populations ascribed to different tautomers. Three photoproducts were resolved and originates from four independent subpopulations, each with different dump-induced behavior: Lumi-Go was depleted, Lumi-Gr was unaffected, and Lumi-Gf was enhanced. This suggests that RcaE may be engineered to act either as an in vivo fluorescent probe (after single-pump excitation) or as an in vivo optogenetic sample (after pump and dump excitation).
†Department of Chemistry and ‡Department of Molecular and Cell Biology, University of California, Davis One Shields Avenue, Davis, California 95616, United States.
Sean M
SM
Gottlieb
†Department of Chemistry and ‡Department of Molecular and Cell Biology, University of California, Davis One Shields Avenue, Davis, California 95616, United States.
Che-Wei
CW
Chang
†Department of Chemistry and ‡Department of Molecular and Cell Biology, University of California, Davis One Shields Avenue, Davis, California 95616, United States.
Shelley S
SS
Martin
†Department of Chemistry and ‡Department of Molecular and Cell Biology, University of California, Davis One Shields Avenue, Davis, California 95616, United States.
Nathan C
NC
Rockwell
†Department of Chemistry and ‡Department of Molecular and Cell Biology, University of California, Davis One Shields Avenue, Davis, California 95616, United States.
J Clark
JC
Lagarias
†Department of Chemistry and ‡Department of Molecular and Cell Biology, University of California, Davis One Shields Avenue, Davis, California 95616, United States.
Delmar S
DS
Larsen
cyanobacteriochromes; phytochromes; pump−dump−probe; ultrafast dynamics