A molecular basis for the differential roles of Bub1 and BubR1 in the spindle assembly checkpoint
Katharina Overlack,
Ivana Primorac,
Mathijs Vleugel,
Veronica Krenn,
Stefano Maffini,
Ingrid Hoffmann,
Geert J P L Kops,
Andrea Musacchio
Affiliations
Katharina Overlack
Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
Ivana Primorac
Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
Mathijs Vleugel
Molecular Cancer Research, University Medical Center Utrecht, Utrecht, Netherlands
Veronica Krenn
Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
Stefano Maffini
Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
Ingrid Hoffmann
Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
Geert J P L Kops
Department of Molecular Cancer Research, University Medical Center Utrecht, Utrecht, Netherlands; Department of Medical Oncology, University Medical Center Utrecht, Utrecht, Netherlands; Cancer Genomics Netherlands, University Medical Center, Utrecht, Netherlands; Department of Biology, Utrecht University, Utrecht, Netherlands; Netherlands Proteomics Center, Utrecht, Netherlands
Andrea Musacchio
Department of Mechanistic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany; Centre for Medical Biotechnology, University Duisburg-Essen, Essen, Germany
The spindle assembly checkpoint (SAC) monitors and promotes kinetochore–microtubule attachment during mitosis. Bub1 and BubR1, SAC components, originated from duplication of an ancestor gene. Subsequent sub-functionalization established subordination: Bub1, recruited first to kinetochores, promotes successive BubR1 recruitment. Because both Bub1 and BubR1 hetero-dimerize with Bub3, a targeting adaptor for phosphorylated kinetochores, the molecular basis for such sub-functionalization is unclear. We demonstrate that Bub1, but not BubR1, enhances binding of Bub3 to phosphorylated kinetochores. Grafting a short motif of Bub1 onto BubR1 promotes Bub1-independent kinetochore recruitment of BubR1. This gain-of-function BubR1 mutant cannot sustain a functional checkpoint. We demonstrate that kinetochore localization of BubR1 relies on direct hetero-dimerization with Bub1 at a pseudo-symmetric interface. This pseudo-symmetric interaction underpins a template–copy relationship crucial for kinetochore–microtubule attachment and SAC signaling. Our results illustrate how gene duplication and sub-functionalization shape the workings of an essential molecular network.
