title: Photoinduced formation of flavin radicals in BLUF domains lacking the central glutamine.
abstract: Blue light receptors using FAD (BLUFs) facilitate blue light-induced signal transduction via light-induced rearrangement of hydrogen bonds between the flavin chromophore and a conserved glutamine side chain. Here, we investigated the photochemistry of the BLUF domain Slr1694 from Synechocystis sp. in which the glutamine side chain was removed. Without the glutamine, no red-shifted signaling state is formed, but light-induced proton-coupled electron transfer between protein and flavin takes place similarly as for the wild-type protein. However, the lifetime of the neutral flavin semiquinone-tyrosyl radical pair is greatly prolonged from < 100 ps to several nanoseconds, which indicates that the formation of radical intermediates drives the hydrogen bond rearrangement in BLUF photoactivation. Moreover, glutamine plays a central role in the molecular organization of the hydrogen bond network in the flavin-binding pocket, as its removal enhances electron transfer from tyrosine to the excited flavin, and enables competing electron transfer from a nearby tryptophan.
authors.affiliation: Institut für Biologie/Experimentelle Biophysik, Humboldt Universität zu Berlin, Berlin, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Fudim
authors.affiliation: Institut für Biologie/Experimentelle Biophysik, Humboldt Universität zu Berlin, Berlin, Germany.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Mehlhorn
authors.affiliation: Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Berthold
authors.affiliation: Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.|Freiburg Institute for Advanced Studies (FRIAS), Albert-Ludwigs-Universität Freiburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weber
authors.affiliation: Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany.|Inorganic Chemistry Laboratory, University of Oxford, UK.
authors.forename: Erik
authors.initials: E
authors.lastname: Schleicher
authors.affiliation: Biophysics Section, Department of Physics and Astronomy, Faculty of Sciences, VU University, Amsterdam, The Netherlands.
authors.forename: John T M
authors.initials: JT
authors.lastname: Kennis
authors.affiliation: Institut für Biologie/Experimentelle Biophysik, Humboldt Universität zu Berlin, Berlin, Germany.|Biophysics Section, Department of Physics and Astronomy, Faculty of Sciences, VU University, Amsterdam, The Netherlands.
authors.forename: Tilo
authors.initials: T
authors.lastname: Mathes
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005415:Flavins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D005973:Glutamine / Q000737:chemistry; D006860:Hydrogen Bonding; D008027:Light; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D055668:Photochemical Processes; D020283:Photoreceptors, Microbial / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000528:radiation effects; D015398:Signal Transduction; D013053:Spectrophotometry; D046939:Synechocystis / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*
chemical_list: D001426:Bacterial Proteins; D005415:Flavins; D005609:Free Radicals; D020283:Photoreceptors, Microbial; D011994:Recombinant Proteins; D005973:Glutamine
keywords: flavin; photoreceptor; proton-coupled electron transfer; spin-correlated radical pair; ultrafast spectroscopy