title: The photoinitiated reaction pathway of full-length cyanobacteriochrome Tlr0924 monitored over 12 orders of magnitude.
abstract: The coupling of photochemistry to protein chemical and structural change is crucial to biological light-activated signaling mechanisms. This is typified by cyanobacteriochromes (CBCRs), members of the phytochrome superfamily of photoreceptors that exhibit a high degree of spectral diversity, collectively spanning the entire visible spectrum. CBCRs utilize a basic E/Z isomerization of the bilin chromophore as the primary step in their photocycle, which consists of reversible photoconversion between two photostates. Despite intense interest in these photoreceptors as signal transduction modules a complete description of light-activated chemical and structural changes has not been reported. The CBCR Tlr0924 contains both phycocyanobilin and phycoviolobilin chromophores, and these two species photoisomerize in parallel via spectrally and kinetically equivalent intermediates before the second step of the photoreaction where the reaction pathways diverge, the loss of a thioether linkage to a conserved cysteine residue occurs, and the phycocyanobilin reaction terminates in a red-absorbing state, whereas the phycoviolobilin reaction proceeds more rapidly to a final green-absorbing state. Here time-resolved visible transient absorption spectroscopy (femtosecond to second) has been used, in conjunction with time-resolved IR spectroscopy (femtosecond to nanosecond) and cryotrapping techniques, to follow the entire photoconversion of the blue-absorbing states to the green- and red-absorbing states of the full-length form of Tlr0924 CBCR. Our analysis shows that Tlr0924 undergoes an unprecedented long photoreaction that spans from picoseconds to seconds. We show that the thermally driven, long timescale changes are less complex than those reported for the red/far-red photocycles of the related phytochrome photoreceptors.
authors.affiliation: From the Manchester Institute of Biotechnology and Photon Science Institute, Faculty of Life Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom and.
authors.forename: Anna F E
authors.initials: AF
authors.lastname: Hauck
authors.affiliation: From the Manchester Institute of Biotechnology and Photon Science Institute, Faculty of Life Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom and.
authors.forename: Samantha J O
authors.initials: SJ
authors.lastname: Hardman
authors.affiliation: From the Manchester Institute of Biotechnology and Photon Science Institute, Faculty of Life Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom and.
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Kutta
authors.affiliation: the Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Harwell Oxford, Didcot OX11 0QX, United Kingdom.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Greetham
authors.affiliation: From the Manchester Institute of Biotechnology and Photon Science Institute, Faculty of Life Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom and.
authors.forename: Derren J
authors.initials: DJ
authors.lastname: Heyes
authors.affiliation: From the Manchester Institute of Biotechnology and Photon Science Institute, Faculty of Life Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom and nigel.scrutton@manchester.ac.uk.
authors.forename: Nigel S
authors.initials: NS
authors.lastname: Scrutton
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D000458:Cyanobacteria / Q000737:chemistry*; D008027:Light; D055668:Photochemical Processes; D010860:Pigments, Biological / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D010860:Pigments, Biological
keywords: Biophysics; Cyanobacteria; Photobiology; Spectroscopy; Ultraviolet-visible Spectroscopy (UV-visible Spectroscopy)