title: Signaling-State Formation Mechanism of a BLUF Protein PapB from the Purple Bacterium Rhodopseudomonas palustris Studied by Femtosecond Time-Resolved Absorption Spectroscopy.
abstract: We studied the signaling-state formation of a BLUF (blue light using FAD) protein, PapB, from the purple bacterium Rhodopseudomonas palustris, using femtosecond time-resolved absorption spectroscopy. Upon photoexcitation of the dark state, FADH(•) (neutral flavin semiquinone FADH radical) was observed as the intermediate before the formation of the signaling state. The kinetic analysis based on singular value decomposition showed that FADH(•) mediates the signaling-state formation, showing that PapB is the second example of FADH(•)-mediated formation of the signaling state after Slr1694 (M. Gauden et al. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 10895-10900). The mechanism of the signaling-state formation is discussed on the basis of the comparison between femtosecond time-resolved absorption spectra of the dark state and those obtained by exciting the signaling state. FADH(•) was observed also with excitation of the signaling state, and surprisingly, the kinetics of FADH(•) was indistinguishable from the case of exciting the dark state. This result suggests that the hydrogen bond environment in the signaling state is realized before the formation of FADH(•) in the photocycle of PapB.
authors.affiliation: Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Tomotsumi
authors.initials: T
authors.lastname: Fujisawa
authors.affiliation: Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.|Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takeuchi
authors.affiliation: Center for Biological Resources and Informatics, and Earth-Life Science Institute, Tokyo Institute of Technology , Yokohama 226-8501, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Masuda
authors.affiliation: Molecular Spectroscopy Laboratory, RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.|Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), RIKEN , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Tahei
authors.initials: T
authors.lastname: Tahara
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D006860:Hydrogen Bonding; D012241:Rhodopseudomonas / Q000378:metabolism*; D015398:Signal Transduction; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D001426:Bacterial Proteins