title: Heterogeneous photodynamics of the pfr state in the cyanobacterial phytochrome Cph1.
abstract: Femtosecond photodynamics of the Pfr form of the red/far-red phytochrome N-terminal PAS-GAF-PHY photosensory core module of the cyanobacterial phytochrome Cph1 (termed Cph1Δ) from Synechocystis were resolved with visible broadband transient absorption spectroscopy. Multiphasic generation dynamics via global target analysis revealed parallel evolution of two pathways with distinct excited- and ground-state kinetics. These measurements resolved two subpopulations: a majority subpopulation with fast excited-state decay and slower ground-state dynamics, corresponding to previous descriptions of Pfr dynamics, and a minority subpopulation with slower excited-state decay and faster ground-state primary dynamics. Both excited-state subpopulations generated the isomerized, red-shifted Lumi-Ff photoproduct (715 nm); subsequent ground-state evolution to a blue-shifted Meta-Fr population (635 nm) proceeded on 3 ps and 1.5 ns time scales for the two subpopulations. Meta-Fr was spectrally similar to a recently described photoinactive fluorescent subpopulation of Pr ((Fluor)Pr). Thus, the reverse Pfr to Pr photoconversion of Cph1Δ involves minor structural deformation of Meta-Fr to generate the fluorescent, photochemically refractory form of Pr, with slower subsequent equilibration with the photoactive Pr subpopulation ((Photo)Pr).
authors.affiliation: Department of Chemistry and ‡Department of Molecular and Cell Biology, University of California , One Shields Avenue, Davis, California 95616, United States.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Kim
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Rockwell
authors.forename: Shelley S
authors.initials: SS
authors.lastname: Martin
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
authors.forename: Delmar S
authors.initials: DS
authors.lastname: Larsen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D055668:Photochemical Processes; D020283:Photoreceptors, Microbial; D010834:Phytochrome / Q000737:chemistry*; D011494:Protein Kinases / Q000737:chemistry*; D046939:Synechocystis / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; D010834:Phytochrome; D011494:Protein Kinases; C413623:Cph1 phytochrome protein, bacteria