title: Emi1 preferentially inhibits ubiquitin chain elongation by the anaphase-promoting complex.
abstract: The anaphase-promoting complex (APC) is the crucial ubiquitin ligase targeting the regulatory machinery of the cell cycle. Emi1, a major modulator of APC activity, is thought to act competitively as a pseudosubstrate. We show that the modulation of APC activity is more subtle: Emi1 inhibits ubiquitylation at both substrate binding and separately at the step of ubiquitin transfer to APC-bound substrates. The zinc-binding region of Emi1 allows multiple monoubiquitylation of substrates, but preferentially suppresses the ubiquitin chain elongation by UBCH10. Furthermore, the carboxy-terminal tail of Emi1 antagonizes chain elongation by Ube2S, by competitively preventing its binding to the APC cullin subunit through electrostatic interaction. Combinatorially, Emi1 effectively stabilizes APC substrates by suppressing ubiquitin chain extension. Deubiquitylating enzymes can then convert inhibited substrates to their basal state. Chain elongation may be a particularly sensitive step for controlling degradation, and this study provides the first kinetic evidence for how it is inhibited.
authors.affiliation: Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, Massachusetts 02115, USA.
authors.forename: Weiping
authors.initials: W
authors.lastname: Wang
authors.forename: Marc W
authors.initials: MW
authors.lastname: Kirschner
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000378:metabolism; D064173:Anaphase-Promoting Complex-Cyclosome; D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D044783:F-Box Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008938:Mitosis / Q000502:physiology; D010441:Peptide Chain Elongation, Translational / Q000502:physiology*; D011485:Protein Binding; D055672:Static Electricity; D025801:Ubiquitin / Q000378:metabolism*; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C555337:APC protein, human; D025601:Adenomatous Polyposis Coli Protein; D018797:Cell Cycle Proteins; D044783:F-Box Proteins; C498960:FBXO5 protein, human; D025801:Ubiquitin; C105156:UBE2C protein, human; C544962:Ube2S protein, human; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome