title: Flavin reduction activates Drosophila cryptochrome.
abstract: Entrainment of circadian rhythms in higher organisms relies on light-sensing proteins that communicate to cellular oscillators composed of delayed transcriptional feedback loops. The principal photoreceptor of the fly circadian clock, Drosophila cryptochrome (dCRY), contains a C-terminal tail (CTT) helix that binds beside a FAD cofactor and is essential for light signaling. Light reduces the dCRY FAD to an anionic semiquinone (ASQ) radical and increases CTT proteolytic susceptibility but does not lead to CTT chemical modification. Additional changes in proteolytic sensitivity and small-angle X-ray scattering define a conformational response of the protein to light that centers at the CTT but also involves regions remote from the flavin center. Reduction of the flavin is kinetically coupled to CTT rearrangement. Chemical reduction to either the ASQ or the fully reduced hydroquinone state produces the same conformational response as does light. The oscillator protein Timeless (TIM) contains a sequence similar to the CTT; the corresponding peptide binds dCRY in light and protects the flavin from oxidation. However, TIM mutants therein still undergo dCRY-mediated degradation. Thus, photoreduction to the ASQ releases the dCRY CTT and promotes binding to at least one region of TIM. Flavin reduction by either light or cellular reductants may be a general mechanism of CRY activation.
authors.affiliation: Department of Chemistry and Chemical Biology and Biotechnology Resource Center, Cornell University, Ithaca, NY 14853.
authors.forename: Anand T
authors.initials: AT
authors.lastname: Vaidya
authors.forename: Deniz
authors.initials: D
authors.lastname: Top
authors.forename: Craig C
authors.initials: CC
authors.lastname: Manahan
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Tokuda
authors.forename: Sheng
authors.initials: S
authors.lastname: Zhang
authors.forename: Lois
authors.initials: L
authors.lastname: Pollack
authors.forename: Michael W
authors.initials: MW
authors.lastname: Young
authors.forename: Brian R
authors.initials: BR
authors.lastname: Crane
mesh_terms: D000818:Animals; D057906:Circadian Clocks / Q000502:physiology / Q000528:radiation effects; D056931:Cryptochromes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D011485:Protein Binding / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction / Q000502:physiology* / Q000528:radiation effects
chemical_list: D056931:Cryptochromes; D029721:Drosophila Proteins; D005136:Eye Proteins; C119828:cry protein, Drosophila; C096445:tim protein, Drosophila; D005182:Flavin-Adenine Dinucleotide
keywords: photolyase; protein-protein interaction; redox