SCF Ubiquitin Ligase Targets Cryptochromes at Their Cofactor Pocket

1] Department of Pharmacology, Box 357280, University of Washington, Seattle, Washington 98195, USA [2] Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195, USA.
Nature (Impact Factor: 42.35). 03/2013; 496(7443). DOI: 10.1038/nature11964
Source: PubMed

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.

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Available from: Nabiha Huq Saifee, Jun 22, 2014
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    • "Our structure also shows that binding of FBXL3 or PER2 to CRY is mutually exclusive and suggests that PER2 stabilizes CRY1 by shielding it from FBXL3 . Strikingly , neither mPER2 ( this study ) nor FBXL3 ( Xing et al . , 2013 ) binds in close proximity of the AMPK phosphorylation site Ser71 , suggesting that AMPK regulates PER2 and FBXL3 binding in a more indirect manner . Notably , Cys412 appears highly reactive in switching functions because it not only forms the intramolecular disulfide bond to Cys363 in apo - mCRY1 but also an intermolecular disul - fide"
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