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Tyrosine 263 in Cyanobacterial Phytochrome C ph1 Optimizes Photochemistry at the prelumi‐ R →lumi‐R Step
Author(s) -
Sineshchekov Vitaly,
Mailliet Joel,
Psakis Georgios,
Feilke Kathleen,
Kopycki Jakub,
Zeidler Mathias,
Essen LarsOliver,
Hughes Jon
Publication year - 2014
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12263
Subject(s) - chemistry , intramolecular force , photochemistry , quantum yield , phytochrome , conical intersection , fluorescence , stereochemistry , molecule , physics , biology , quantum mechanics , red light , botany , organic chemistry
We report a low‐temperature fluorescence spectroscopy study of the PAS ‐ GAF ‐ PHY sensory module of C ph1 phytochrome, its Y 263 F mutant (both with known 3D structures) as well as Y 263 H and Y 263 S to connect their photochemical parameters with intramolecular interactions. None of the holoproteins showed photochemical activity at low temperature, and the activation barriers for the Pr→lumi‐R photoreaction (2.5–3.1 kJ mol −1 ) and fluorescence quantum yields (0.29–0.42) were similar. The effect of the mutations on Pr→Pfr photoconversion efficiency (Φ Pr→Pfr ) was observed primarily at the prelumi‐R S 0 bifurcation point corresponding to the conical intersection of the energy surfaces at which the molecule relaxes to form lumi‐R or Pr, lowering Φ Pr→Pfr from 0.13 in the wild type to 0.05–0.07 in the mutants. We suggest that the E a activation barrier in the Pr* S 1 excited state might correspond to the D‐ring ( C 19) carbonyl – H 290 hydrogen bond or possibly to the hindrance caused by the C13 1 /C17 1 methyl groups of the C and D rings. The critical role of the tyrosine hydroxyl group can be at the prelumi‐R bifurcation point to optimize the yield of the photoprocess and energy storage in the form of lumi‐R for subsequent rearrangement processes culminating in Pfr formation.