Abstract
In the dividing eukaryotic cell, the spindle assembly checkpoint (SAC) ensures that each daughter cell inherits an identical set of chromosomes. The SAC coordinates the correct attachment of sister chromatid kinetochores to the mitotic spindle with activation of the anaphase-promoting complex (APC/C), the E3 ubiquitin ligase responsible for initiating chromosome separation. In response to unattached kinetochores, the SAC generates the mitotic checkpoint complex (MCC), which inhibits the APC/C and delays chromosome segregation. By cryo-electron microscopy, here we determine the near-atomic resolution structure of a human APC/C–MCC complex (APC/C(MCC)). Degron-like sequences of the MCC subunit BubR1 block degron recognition sites on Cdc20, the APC/C coactivator subunit responsible for substrate interactions. BubR1 also obstructs binding of the initiating E2 enzyme UbcH10 to repress APC/C ubiquitination activity. Conformational variability of the complex enables UbcH10 association, and structural analysis shows how the Cdc20 subunit intrinsic to the MCC (Cdc20(MCC)) is ubiquitinated, a process that results in APC/C reactivation when the SAC is silenced.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Anaphase-Promoting Complex-Cyclosome / antagonists & inhibitors*
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Anaphase-Promoting Complex-Cyclosome / chemistry
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Anaphase-Promoting Complex-Cyclosome / metabolism
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Anaphase-Promoting Complex-Cyclosome / ultrastructure*
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Biocatalysis
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Cdc20 Proteins / chemistry
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Cdc20 Proteins / metabolism
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Cdc20 Proteins / ultrastructure
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Cell Cycle Proteins / metabolism
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Chromosome Segregation
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Cryoelectron Microscopy*
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Humans
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Kinetochores / metabolism
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M Phase Cell Cycle Checkpoints / physiology*
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Models, Molecular
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Protein Binding
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Protein Conformation
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Protein Serine-Threonine Kinases / chemistry
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Protein Serine-Threonine Kinases / metabolism
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Protein Serine-Threonine Kinases / ultrastructure
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Protein Subunits / chemistry
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Protein Subunits / metabolism
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Spindle Apparatus / chemistry
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Spindle Apparatus / metabolism*
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Spindle Apparatus / ultrastructure*
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Structure-Activity Relationship
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Ubiquitin-Conjugating Enzymes / chemistry
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Ubiquitin-Conjugating Enzymes / metabolism
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Ubiquitin-Conjugating Enzymes / ultrastructure
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Ubiquitin-Protein Ligases / metabolism
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Ubiquitination
Substances
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ANAPC15 protein, human
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Cdc20 Proteins
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Cell Cycle Proteins
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Protein Subunits
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CDC20 protein, human
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UBE2C protein, human
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Ubiquitin-Conjugating Enzymes
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Anaphase-Promoting Complex-Cyclosome
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Ubiquitin-Protein Ligases
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BUB1 protein, human
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Protein Serine-Threonine Kinases