Catalytic assembly of the mitotic checkpoint inhibitor BubR1-Cdc20 by a Mad2-induced functional switch in Cdc20

Mol Cell. 2013 Jul 11;51(1):92-104. doi: 10.1016/j.molcel.2013.05.019. Epub 2013 Jun 20.


The mitotic checkpoint acts to maintain chromosome content by generation of a diffusible anaphase inhibitor. Unattached kinetochores catalyze a conformational shift in Mad2, converting an inactive open form into a closed form that can capture Cdc20, the mitotic activator of the APC/C ubiquitin ligase. Mad2 binding is now shown to promote a functional switch in Cdc20, exposing a previously inaccessible site for binding to BubR1's conserved Mad3 homology domain. BubR1, but not Mad2, binding to APC/C(Cdc20) is demonstrated to inhibit ubiquitination of cyclin B. Closed Mad2 is further shown to catalytically amplify production of BubR1-Cdc20 without necessarily being part of the complex. Thus, the mitotic checkpoint is produced by a cascade of two catalytic steps: an initial step acting at unattached kinetochores to produce a diffusible Mad2-Cdc20 intermediate and a diffusible step in which that intermediate amplifies production of BubR1-Cdc20, the inhibitor of cyclin B ubiquitination, by APC/C(Cdc20).

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Calcium-Binding Proteins / metabolism
  • Calcium-Binding Proteins / physiology*
  • Cdc20 Proteins
  • Cell Cycle Proteins / metabolism*
  • Cell Cycle Proteins / physiology*
  • HeLa Cells
  • Humans
  • Kinetochores / metabolism
  • M Phase Cell Cycle Checkpoints / physiology*
  • Mad2 Proteins
  • Models, Genetic
  • Protein-Serine-Threonine Kinases / metabolism*
  • Repressor Proteins / metabolism
  • Repressor Proteins / physiology*


  • Calcium-Binding Proteins
  • Cdc20 Proteins
  • Cell Cycle Proteins
  • MAD2L1 protein, human
  • Mad2 Proteins
  • Repressor Proteins
  • CDC20 protein, human
  • BUB1 protein, human
  • Bub1 spindle checkpoint protein
  • Protein-Serine-Threonine Kinases