title: Cryptochrome blue light photoreceptors are activated through interconversion of flavin redox states.
abstract: Cryptochromes are blue light-sensing photoreceptors found in plants, animals, and humans. They are known to play key roles in the regulation of the circadian clock and in development. However, despite striking structural similarities to photolyase DNA repair enzymes, cryptochromes do not repair double-stranded DNA, and their mechanism of action is unknown. Recently, a blue light-dependent intramolecular electron transfer to the excited state flavin was characterized and proposed as the primary mechanism of light activation. The resulting formation of a stable neutral flavin semiquinone intermediate enables the photoreceptor to absorb green/yellow light (500-630 nm) in addition to blue light in vitro. Here, we demonstrate that Arabidopsis cryptochrome activation by blue light can be inhibited by green light in vivo consistent with a change of the cofactor redox state. We further characterize light-dependent changes in the cryptochrome1 (cry1) protein in living cells, which match photoreduction of the purified cry1 in vitro. These experiments were performed using fluorescence absorption/emission and EPR on whole cells and thereby represent one of the few examples of the active state of a known photoreceptor being monitored in vivo. These results indicate that cry1 activation via blue light initiates formation of a flavosemiquinone signaling state that can be converted by green light to an inactive form. In summary, cryptochrome activation via flavin photoreduction is a reversible mechanism novel to blue light photoreceptors. This photocycle may have adaptive significance for sensing the quality of the light environment in multiple organisms.
authors.affiliation: Université Paris VI, FRE-CNRS 2846, Casier 156, 4 Place Jussieu, 75005 Paris, France.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bouly
authors.affiliation: Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Erik
authors.initials: E
authors.lastname: Schleicher
authors.affiliation: FB Biologie-Pflanzenphysiologie, Philipps-Universität, Karl-von-Frisch-Strasse 8, 35032 Marburg, Germany.
authors.forename: Maribel
authors.initials: M
authors.lastname: Dionisio-Sese
authors.affiliation: Université Paris VI, FRE-CNRS 2846, Casier 156, 4 Place Jussieu, 75005 Paris, France; Unit Plant Hormone Signaling and Bio-imaging, Department of Molecular Genetics, Ghent University, Ledeganckstraat 35, B-9000 Ghent, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: Vandenbussche
authors.affiliation: Pennsylvania State University, Media, Pennsylvania 19063.
authors.forename: Dominique
authors.initials: D
authors.lastname: Van Der Straeten
authors.affiliation: Université Paris VI, FRE-CNRS 2846, Casier 156, 4 Place Jussieu, 75005 Paris, France.
authors.forename: Nadia
authors.initials: N
authors.lastname: Bakrim
authors.affiliation: FB Biologie-Pflanzenphysiologie, Philipps-Universität, Karl-von-Frisch-Strasse 8, 35032 Marburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Meier
authors.affiliation: FB Biologie-Pflanzenphysiologie, Philipps-Universität, Karl-von-Frisch-Strasse 8, 35032 Marburg, Germany.
authors.forename: Alfred
authors.initials: A
authors.lastname: Batschauer
authors.affiliation: FB Biologie-Pflanzenphysiologie, Philipps-Universität, Karl-von-Frisch-Strasse 8, 35032 Marburg, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Galland
authors.affiliation: Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Bittl
authors.affiliation: Université Paris VI, FRE-CNRS 2846, Casier 156, 4 Place Jussieu, 75005 Paris, France; Pennsylvania State University, Media, Pennsylvania 19063. Electronic address: ahmad@ccr.jussieu.fr.
authors.forename: Margaret
authors.initials: M
authors.lastname: Ahmad
mesh_terms: D017360:Arabidopsis / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D001683:Biological Clocks / Q000502:physiology / Q000528:radiation effects; D056931:Cryptochromes; D005415:Flavins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D005420:Flavoproteins / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D010084:Oxidation-Reduction / Q000528:radiation effects; D010786:Photoreceptor Cells / Q000737:chemistry / Q000378:metabolism* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; C538963:CRY1 protein, human; D056931:Cryptochromes; D005415:Flavins; D005420:Flavoproteins