title: Detailed insight into the ultrafast photoconversion of the cyanobacteriochrome Slr1393 from Synechocystis sp.
abstract: The initial light-induced processes of the photochromic, phycocyanobilin-binding GAF domain of Slr1393 from Synechocystis sp. PCC6803 have been studied by ultrafast transient absorption spectroscopy. We use lifetime density analysis as a model-independent method for the evolution of the experimental data, which gives a comprehensive overview of the excitation wavelength dependence of the photoconversion kinetics. The method is particularly suitable for this highly complex and not purely exponential kinetics. In contrast to previously studied cyanobacteriochromes (CBCRs), here both the red- and the green-absorbing forms show significantly slower reaction dynamics, which proceed also via ground state intermediates. The photoconversion of the green-absorbing form is faster than that of the red state, which allowed a clear detection of the primary photoproduct Lumi-G. Strong coherent oscillations of the recorded transient absorption due to wavepacket motion on the excited state potential energy surface were observed and analyzed for both (red and green) forms of Slr1393g3. The vibrational modes responsible for the coherent oscillations could play a role in the dynamics of the initially heterogeneous excited state (ES) population and direct the system towards the minima on the potential energy surface that determine the ES decay pathway. Furthermore, the coherent oscillations appear to be a common feature of bilin-based photoreceptors and thus deserve further attention. The investigated CBCR exhibits an extraordinary high level of heterogeneity due to the remarkable flexibility of the phycocyanobilin and the protein binding pocket. These properties should allow spectrally tuned response to the light stimuli and thus have significant biological implications.
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University, Frankfurt am Main, Germany.
authors.forename: Chavdar
authors.initials: C
authors.lastname: Slavov
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Mülheim a.d. Ruhr, Germany; Department of Chemistry, University of Toronto, Canada.
authors.forename: Xiuling
authors.initials: X
authors.lastname: Xu
authors.affiliation: State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan, PR China.
authors.forename: Kai-Hong
authors.initials: KH
authors.lastname: Zhao
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Mülheim a.d. Ruhr, Germany. Electronic address: wolfgang.gaertner@cec.mpg.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gärtner
authors.affiliation: Institute of Physical and Theoretical Chemistry, Goethe University, Frankfurt am Main, Germany. Electronic address: wveitl@theochem.uni-frankfurt.de.
authors.forename: Josef
authors.initials: J
authors.lastname: Wachtveitl
keywords: Cyanobacteriochrome; Lifetime density analysis; Photoisomerization; Photoreceptors; Transient absorption; Ultrafast spectroscopy