期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：37
页码：11536-11540
DOI：10.1073/pnas.1515358112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe mitotic checkpoint system is important to ensure accurate segregation of chromosomes in mitosis. It acts by the formation of a mitotic checkpoint complex (MCC), which inhibits the ubiquitin ligase anaphase-promoting complex/cyclosome (APC/C). When the checkpoint is turned off, MCC is disassembled by the joint action of an ATP-utilizing enzyme, thyroid receptor interacting protein 13 (TRIP13), and a Mad2-binding protein, p31comet. It is not well understood how p31comet targets TRIP13 to disassemble MCC. We show here that p31comet and MCC mutually promote the binding of each other to oligomeric TRIP13 and propose a model for the mode of the action of TRIP13 in MCC disassembly. Thus, the results reveal an important molecular mechanism in the inactivation of the mitotic checkpoint. The AAA-ATPase thyroid hormone receptor interacting protein 13 (TRIP13), jointly with the Mad2-binding protein p31comet, promotes the inactivation of the mitotic (spindle assembly) checkpoint by disassembling the mitotic checkpoint complex (MCC). This checkpoint system ensures the accuracy of chromosome segregation by delaying anaphase until correct bipolar attachment of chromatids to the mitotic spindle is achieved. MCC inhibits the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase that targets for degradation securin, an inhibitor of anaphase initiation. MCC is composed of the checkpoint proteins Mad2, BubR1, and Bub3, in association with the APC/C activator Cdc20. The assembly of MCC in active checkpoint is initiated by the conversion of Mad2 from an open (O-Mad2) to a closed (C-Mad2) conformation, which then binds tightly to Cdc20. Conversely, the disassembly of MCC that takes place when the checkpoint is turned off involves the conversion of C-Mad2 back to O-Mad2. Previously, we found that the latter process is mediated by TRIP13 together with p31comet, but the mode of their interaction remained unknown. Here, we report that the oligomeric form of TRIP13 binds both p31comet and MCC. Furthermore, p31comet and checkpoint complexes mutually promote the binding of each other to oligomeric TRIP13. We propose that p31comet bound to C-Mad2-containing checkpoint complex is the substrate for the ATPase and that the substrate-binding site of TRIP13 is composed of subsites specific for p31comet and C-Mad2-containing complex. The simultaneous occupancy of both subsites is required for high-affinity binding to TRIP13.
