title: The signaling state of Arabidopsis cryptochrome 2 contains flavin semiquinone.
abstract: Cryptochrome (Cry) photoreceptors share high sequence and structural similarity with DNA repair enzyme DNA-photolyase and carry the same flavin cofactor. Accordingly, DNA-photolyase was considered a model system for the light activation process of cryptochromes. In line with this view were recent spectroscopic studies on cryptochromes of the CryDASH subfamily that showed photoreduction of the flavin adenine dinucleotide (FAD) cofactor to its fully reduced form. However, CryDASH members were recently shown to have photolyase activity for cyclobutane pyrimidine dimers in single-stranded DNA, which is absent for other members of the cryptochrome/photolyase family. Thus, CryDASH may have functions different from cryptochromes. The photocycle of other members of the cryptochrome family, such as Arabidopsis Cry1 and Cry2, which lack DNA repair activity but control photomorphogenesis and flowering time, remained elusive. Here we have shown that Arabidopsis Cry2 undergoes a photocycle in which semireduced flavin (FADH(.)) accumulates upon blue light irradiation. Green light irradiation of Cry2 causes a change in the equilibrium of flavin oxidation states and attenuates Cry2-controlled responses such as flowering. These results demonstrate that the active form of Cry2 contains FADH(.) (whereas catalytically active photolyase requires fully reduced flavin (FADH(-))) and suggest that cryptochromes could represent photoreceptors using flavin redox states for signaling differently from DNA-photolyase for photorepair.
authors.affiliation: Fachbereich Biologie-Pflanzenphysiologie, Philipps-Universität, Karl-von-Frisch-Strasse 8, 35032 Marburg, Germany.
authors.forename: Roopa
authors.initials: R
authors.lastname: Banerjee
authors.forename: Erik
authors.initials: E
authors.lastname: Schleicher
authors.forename: Stefan
authors.initials: S
authors.lastname: Meier
authors.forename: Rafael Muñoz
authors.initials: RM
authors.lastname: Viana
authors.forename: Richard
authors.initials: R
authors.lastname: Pokorny
authors.forename: Margaret
authors.initials: M
authors.lastname: Ahmad
authors.forename: Robert
authors.initials: R
authors.lastname: Bittl
authors.forename: Alfred
authors.initials: A
authors.lastname: Batschauer
mesh_terms: D017360:Arabidopsis / Q000737:chemistry* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D003067:Coenzymes / Q000737:chemistry* / Q000378:metabolism; D056931:Cryptochromes; D004260:DNA Repair / Q000502:physiology / Q000528:radiation effects; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005182:Flavin-Adenine Dinucleotide / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D005420:Flavoproteins / Q000737:chemistry* / Q000378:metabolism; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D011740:Pyrimidine Dimers / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology / Q000528:radiation effects; D013056:Spectrophotometry, Ultraviolet
chemical_list: D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D003067:Coenzymes; D056931:Cryptochromes; D004277:DNA, Single-Stranded; D005420:Flavoproteins; D011740:Pyrimidine Dimers; D005182:Flavin-Adenine Dinucleotide; C029276:flavin semiquinone