title: Catalytic assembly of the mitotic checkpoint inhibitor BubR1-Cdc20 by a Mad2-induced functional switch in Cdc20.
abstract: 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).
authors.affiliation: Ludwig Institute for Cancer Research, University of California at San Diego, La Jolla, CA 92093, USA.
authors.forename: Joo Seok
authors.initials: JS
authors.lastname: Han
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Holland
authors.forename: Daniele
authors.initials: D
authors.lastname: Fachinetti
authors.forename: Anita
authors.initials: A
authors.lastname: Kulukian
authors.forename: Bulent
authors.initials: B
authors.lastname: Cetin
authors.forename: Don W
authors.initials: DW
authors.lastname: Cleveland
mesh_terms: D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism* / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D018386:Kinetochores / Q000378:metabolism; D059566:M Phase Cell Cycle Checkpoints / Q000502:physiology*; D064246:Mad2 Proteins; D008957:Models, Genetic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology*
chemical_list: D002135:Calcium-Binding Proteins; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D012097:Repressor Proteins; C577488:CDC20 protein, human; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases