title: Active and silent chromophore isoforms for phytochrome Pr photoisomerization: An alternative evolutionary strategy to optimize photoreaction quantum yields.
abstract: Photoisomerization of a protein bound chromophore is the basis of light sensing of many photoreceptors. We tracked Z-to-E photoisomerization of Cph1 phytochrome chromophore PCB in the Pr form in real-time. Two different phycocyanobilin (PCB) ground state geometries with different ring D orientations have been identified. The pre-twisted and hydrogen bonded PCB(a) geometry exhibits a time constant of 30 ps and a quantum yield of photoproduct formation of 29%, about six times slower and ten times higher than that for the non-hydrogen bonded PCB(b) geometry. This new mechanism of pre-twisting the chromophore by protein-cofactor interaction optimizes yields of slow photoreactions and provides a scaffold for photoreceptor engineering.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Physics, Freie Universität Berlin , Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Linke
authors.affiliation: Department of Physics, Freie Universität Berlin , Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Theodore
authors.initials: T
authors.lastname: von Haimberger
authors.affiliation: Department of Chemistry and Biochemistry, UCLA , 607 Charles E. Young Drive East, Los Angeles, California 90095-1569, USA.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Matute
authors.affiliation: Universität Wien, Institut für Theoretische Chemie , Währinger Str. 17, A-1090 Wien.
authors.forename: Leticia
authors.initials: L
authors.lastname: González
authors.affiliation: Leibniz-Institut für Molekulare Pharmakologie , Robert-Rössle Str. 10, 13125 Berlin, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Schmieder
authors.forename: Karsten
authors.initials: K
authors.lastname: Heyne