title: Rapid E2-E3 assembly and disassembly enable processive ubiquitylation of cullin-RING ubiquitin ligase substrates.
abstract: Degradation by the ubiquitin-proteasome system requires assembly of a polyubiquitin chain upon substrate. However, the structural and mechanistic features that enable template-independent processive chain synthesis are unknown. We show that chain assembly by ubiquitin ligase SCF and ubiquitin-conjugating enzyme Cdc34 is facilitated by the unusual nature of Cdc34-SCF transactions: Cdc34 binds SCF with nanomolar affinity, nevertheless the complex is extremely dynamic. These properties are enabled by rapid association driven by electrostatic interactions between the acidic tail of Cdc34 and a basic 'canyon' in the Cul1 subunit of SCF. Ab initio docking between Cdc34 and Cul1 predicts intimate contact between the tail and the basic canyon, an arrangement confirmed by crosslinking and kinetic analysis of mutants. Basic canyon residues are conserved in both Cul1 paralogs and orthologs, suggesting that the same mechanism underlies processivity for all cullin-RING ubiquitin ligases. We discuss different strategies by which processive ubiquitin chain synthesis may be achieved.
authors: Howard Hughes Medical Institute and the Division of Biology, 156-29, California Institute of Technology, Pasadena, CA 91125, USA.
authors: Gary
authors: G
authors: Kleiger
authors: Anjanabha
authors: A
authors: Saha
authors: Steven
authors: S
authors: Lewis
authors: Brian
authors: B
authors: Kuhlman
authors: Raymond J
authors: RJ
authors: Deshaies
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome; D044842:Cullin Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000737:chemistry / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000737:chemistry / Q000378:metabolism*; D054875:Ubiquitination; D015003:Yeasts / Q000378:metabolism
chemical_list: C100318:Cullin 1; D044842:Cullin Proteins; D025801:Ubiquitin; C577447:CDC34 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044843:SKP Cullin F-Box Protein Ligases