BUBR1 and closed MAD2 (C-MAD2) interact directly to assemble a functional mitotic checkpoint complex

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• The mitotic checkpoint is crucial for maintaining genomic stability by preventing chromosome missegregation during mitosis.
• The mitotic checkpoint complex (MCC), comprising BUBR1, BUB3, CDC20, and MAD2, inhibits the anaphase-promoting complex/cyclosome (APC/C) to ensure proper chromosome attachment and alignment.

Purpose of the Study:

• To elucidate the mechanisms underlying MCC assembly and its interaction with APC/C.
• To identify the specific interactions critical for MCC function in mitotic checkpoint control.

Main Methods:

• Investigated the interaction between BUBR1 and closed MAD2 (C-MAD2).
• Utilized site-directed mutagenesis to identify key residues in C-MAD2 for BUBR1 interaction.
• Examined the role of these residues in MAD2 dimerization and binding to p31(comet).

Main Results:

• Identified a novel and essential interaction between BUBR1 and C-MAD2 for MCC-mediated APC/C inhibition.
• Demonstrated that Arg(133) and Gln(134) in C-MAD2 are critical for BUBR1 binding.
• Found that these residues are also vital for MAD2 dimerization and interaction with the silencing protein p31(comet).

Conclusions:

• The integrity of the MCC is fundamental for its inhibitory activity on APC/C.
• The identified BUBR1-C-MAD2 interaction is essential for mitotic checkpoint function.
• The MAD2 αC helix plays a pivotal role in modulating both mitotic checkpoint activation and silencing.