title: SCF(FBXL3) ubiquitin ligase targets cryptochromes at their cofactor pocket.
abstract: The cryptochrome (CRY) flavoproteins act as blue-light receptors in plants and insects, but perform light-independent functions at the core of the mammalian circadian clock. To drive clock oscillations, mammalian CRYs associate with the Period proteins (PERs) and together inhibit the transcription of their own genes. The SCF(FBXL3) ubiquitin ligase complex controls this negative feedback loop by promoting CRY ubiquitination and degradation. However, the molecular mechanisms of their interactions and the functional role of flavin adenine dinucleotide (FAD) binding in CRYs remain poorly understood. Here we report crystal structures of mammalian CRY2 in its apo, FAD-bound and FBXL3-SKP1-complexed forms. Distinct from other cryptochromes of known structures, mammalian CRY2 binds FAD dynamically with an open cofactor pocket. Notably, the F-box protein FBXL3 captures CRY2 by simultaneously occupying its FAD-binding pocket with a conserved carboxy-terminal tail and burying its PER-binding interface. This novel F-box-protein-substrate bipartite interaction is susceptible to disruption by both FAD and PERs, suggesting a new avenue for pharmacological targeting of the complex and a multifaceted regulatory mechanism of CRY ubiquitination.
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Weiman
authors.initials: W
authors.lastname: Xing
authors.forename: Luca
authors.initials: L
authors.lastname: Busino
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Hinds
authors.forename: Samuel T
authors.initials: ST
authors.lastname: Marionni
authors.forename: Nabiha H
authors.initials: NH
authors.lastname: Saifee
authors.forename: Matthew F
authors.initials: MF
authors.lastname: Bush
authors.forename: Michele
authors.initials: M
authors.lastname: Pagano
authors.forename: Ning
authors.initials: N
authors.lastname: Zheng
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D056931:Cryptochromes / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004255:Deoxyribodipyrimidine Photo-Lyase / Q000737:chemistry; D004331:Drosophila melanogaster / Q000737:chemistry; D044783:F-Box Proteins / Q000737:chemistry / Q000378:metabolism*; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D044786:S-Phase Kinase-Associated Proteins / Q000737:chemistry / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000737:chemistry / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001059:Apoproteins; C538967:Cry2 protein, mouse; D056931:Cryptochromes; D044783:F-Box Proteins; C519795:FBXL3 protein, human; C519794:Fbxl3 protein, mouse; D044786:S-Phase Kinase-Associated Proteins; C097351:SKP1 protein, human; D005182:Flavin-Adenine Dinucleotide; D044843:SKP Cullin F-Box Protein Ligases; D004255:Deoxyribodipyrimidine Photo-Lyase