title: Electronic transitions and heterogeneity of the bacteriophytochrome Pr absorption band: An angle balanced polarization resolved femtosecond VIS pump-IR probe study.
abstract: Photoisomerization of biliverdin (BV) chromophore triggers the photoresponse in native Agp1 bacteriophytochrome. We discuss heterogeneity in phytochrome Pr form to account for the shape of the absorption profile. We investigated different regions of the absorption profile by angle balanced polarization resolved femtosecond VIS pump-IR probe spectroscopy. We studied the Pr form of Agp1 with its natural chromophore and with a sterically locked 18Et-BV (locked Agp1). We followed the dynamics and orientations of the carbonyl stretching vibrations of ring D and ring A in their ground and electronically excited states. Photoisomerization of ring D is reflected by strong signals of the ring D carbonyl vibration. In contrast, orientational data on ring A show no rotation of ring A upon photoexcitation. Orientational data allow excluding a ZZZasa geometry and corroborates a nontwisted ZZZssa geometry of the chromophore. We found no proof for heterogeneity but identified a new, to our knowledge, electronic transition in the absorption profile at 644 nm (S0→S2). Excitation of the S0→S2 transition will introduce a more complex photodynamics compared with S0→S1 transition. Our approach provides fundamental information on disentanglement of absorption profiles, identification of chromophore structures, and determination of molecular groups involved in the photoisomerization process of photoreceptors.
authors.affiliation: Freie Universität Berlin, Department of Physics, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Linke
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Benjamin
authors.initials: B
authors.lastname: Zienicke
authors.forename: Mostafa A S
authors.initials: MA
authors.lastname: Hammam
authors.forename: Theodore
authors.initials: T
authors.lastname: von Haimberger
authors.forename: Angelica
authors.initials: A
authors.lastname: Zacarias
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Inomata
authors.forename: Tilman
authors.initials: T
authors.lastname: Lamparter
authors.forename: Karsten
authors.initials: K
authors.lastname: Heyne
mesh_terms: D000042:Absorption; D016960:Agrobacterium tumefaciens / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D004583:Electrons; D015335:Molecular Probes / Q000378:metabolism*; D010834:Phytochrome / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D013997:Time Factors; D014732:Vibration
chemical_list: D001426:Bacterial Proteins; D015335:Molecular Probes; D010834:Phytochrome