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Active and silent chromophore isoforms for phytochrome Pr photoisomerization: An alternative evolutionary strategy to
Yang Yang, Martin Linke1, Theodore von Haimberger1
1Department of Physics, Freie Universität Berlin , Arnimallee 14, 14195 Berlin, Germany.
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.
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