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APC2 Cullin protein and APC11 RING protein comprise the minimal ubiquitin ligase module of the anaphase-promoting complex.

In mitosis, the anaphase-promoting complex (APC) regulates the onset of sister-chromatid separation and exit from mitosis by mediating the ubiquitination and degradation of the securin protein and mitotic cyclins. With the use of a baculoviral expression system, we have reconstituted the ubiquitin ligase activity of human APC. In combination with Ubc4 or UbcH10, a heterodimeric complex of APC2 and APC11 is sufficient to catalyze the ubiquitination of human securin and cyclin B1. However, the minimal APC2/11 ubiquitin ligase module does not possess substrate specificity, because it also ubiquitinates the destruction box deletion mutants of securin and cyclin B1. Both APC11 and UbcH10 bind to the C-terminal cullin homology domain of APC2, whereas Ubc4 interacts with APC11 directly. Zn(2+)-binding and mutagenesis experiments indicate that APC11 binds Zn(2+) at a 1:3 M ratio. Unlike the two Zn(2+) ions of the canonical RING-finger motif, the third Zn(2+) ion of APC11 is not essential for its ligase activity. Surprisingly, with Ubc4 as the E2 enzyme, Zn(2+) ions alone are sufficient to catalyze the ubiquitination of cyclin B1. Therefore, the Zn(2+) ions of the RING finger family of ubiquitin ligases may be directly involved in catalysis.

Pubmed ID: 11739784


  • Tang Z
  • Li B
  • Bharadwaj R
  • Zhu H
  • Ozkan E
  • Hakala K
  • Deisenhofer J
  • Yu H


Molecular biology of the cell

Publication Data

December 12, 2001

Associated Grants

  • Agency: NIGMS NIH HHS, Id: GM-61542

Mesh Terms

  • Amino Acid Sequence
  • Anaphase
  • Anaphase-Promoting Complex-Cyclosome
  • Animals
  • Apc11 Subunit, Anaphase-Promoting Complex-Cyclosome
  • Catalysis
  • Cell Cycle
  • Cyclin B
  • Cyclin B1
  • Enzyme Activation
  • Humans
  • Ligases
  • Molecular Sequence Data
  • Protein Binding
  • Protein Structure, Tertiary
  • Protein Subunits
  • Sequence Homology, Amino Acid
  • Substrate Specificity
  • Ubiquitin
  • Ubiquitin-Conjugating Enzymes
  • Ubiquitin-Protein Ligase Complexes
  • Zinc