title: Structural basis for a reciprocal regulation between SCF and CSN.
abstract: Skp1-Cul1-Fbox (SCF) E3 ligases are activated by ligation to the ubiquitin-like protein Nedd8, which is reversed by the deneddylating Cop9 signalosome (CSN). However, CSN also promotes SCF substrate turnover through unknown mechanisms. Through biochemical and electron microscopy analyses, we determined molecular models of CSN complexes with SCF(Skp2/Cks1) and SCF(Fbw7) and found that CSN occludes both SCF functional sites-the catalytic Rbx1-Cul1 C-terminal domain and the substrate receptor. Indeed, CSN binding prevents SCF interactions with E2 enzymes and a ubiquitination substrate, and it inhibits SCF-catalyzed ubiquitin chain formation independent of deneddylation. Importantly, CSN prevents neddylation of the bound cullin, unless binding of a ubiquitination substrate triggers SCF dissociation and neddylation. Taken together, the results provide a model for how reciprocal regulation sensitizes CSN to the SCF assembly state and inhibits a catalytically competent SCF until a ubiquitination substrate drives its own degradation by displacing CSN, thereby promoting cullin neddylation and substrate ubiquitination.
authors.affiliation: ETH-Zurich, Institute of Biochemistry, Department of Biology, Zurich, Switzerland.
authors.forename: Radoslav I
authors.initials: RI
authors.lastname: Enchev
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Scott
authors.forename: Paula C A
authors.initials: PC
authors.lastname: da Fonseca
authors.forename: Anne
authors.initials: A
authors.lastname: Schreiber
authors.forename: Julie K
authors.initials: JK
authors.lastname: Monda
authors.forename: Brenda A
authors.initials: BA
authors.lastname: Schulman
authors.forename: Matthias
authors.initials: M
authors.lastname: Peter
authors.forename: Edward P
authors.initials: EP
authors.lastname: Morris
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D044842:Cullin Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; C100318:Cullin 1; D044842:Cullin Proteins; D009097:Multienzyme Complexes; C479529:RBX1 protein, human; D025801:Ubiquitin; D044843:SKP Cullin F-Box Protein Ligases