title: Characterization of the Cullin7 E3 ubiquitin ligase--heterodimerization of cullin substrate receptors as a novel mechanism to regulate cullin E3 ligase activity.
abstract: Cul1 and Cul7 are cullin E3 ubiquitin ligase scaffold proteins. Cul1 is known to form a complex with the RING domain protein Rbx1 and one of approximately 70 different F-box proteins. F-box proteins function as substrate receptor subunits and recruit numerous substrates for poly-ubiquitination. Similarly to Cul1, Cul7 interacts with Rbx1, however, only one F-box protein, Fbxw8, has been shown to bind to Cul7. To date only few Cul7 E3 ubiquitin ligase substrates, including cyclin D1, IRS-1 and GRASP65, have been reported, and using Fbxw8 affinity purification, we were unable to identify additional substrate proteins. Here we provide evidence for a model in which Cul7-Rbx1 can promote the ubiquitination of Cul1 substrates by forming high order complexes with Cul1-Rbx1. Binding of Cul1-Rbx1 to Cul7-Rbx1 is mediated via heterodimerization of Fbxw8 with other F-box proteins which function to recruit substrates into the E3 ligase complex. The formation of this high order complex is likely to increase polyubiquitination efficiency.
authors.affiliation: Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Wanpen
authors.initials: W
authors.lastname: Ponyeam
authors.forename: Thilo
authors.initials: T
authors.lastname: Hagen
mesh_terms: D044842:Cullin Proteins / Q000378:metabolism*; D044783:F-Box Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D046912:Multiprotein Complexes / Q000378:metabolism; D000075687:NEDD8 Protein; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011485:Protein Binding; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D054875:Ubiquitination; D014452:Ubiquitins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
chemical_list: C506299:CUL7 protein, human; C100318:Cullin 1; D044842:Cullin Proteins; D044783:F-Box Proteins; C526069:FBXW8 protein, human; D007976:Leupeptins; D046912:Multiprotein Complexes; D000075687:NEDD8 Protein; C082860:NEDD8 protein, human; D061988:Proteasome Inhibitors; D011993:Recombinant Fusion Proteins; D014452:Ubiquitins; D051176:beta Catenin; D044843:SKP Cullin F-Box Protein Ligases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde