Structure of human Mad1 C-terminal domain reveals its involvement in kinetochore targeting

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• The spindle checkpoint is crucial for preventing aneuploidy by ensuring proper chromosome segregation.
• The Mad1-Mad2 complex is central to spindle checkpoint signaling, regulating anaphase onset.
• Mechanisms of Mad1 kinetochore targeting remain largely unknown.

Purpose of the Study:

• To elucidate the structural basis and molecular mechanisms of Mad1 kinetochore targeting.
• To identify the specific domains and interactions involved in Mad1 localization.

Main Methods:

• X-ray crystallography to determine the structure of human Mad1 C-terminal domain (CTD).
• Biochemical assays using Mad1 fragments to assess kinetochore binding.
• Mutagenesis studies to map functional interfaces and identify interacting partners.

Main Results:

• The crystal structure of Mad1 CTD revealed a homodimeric structure with a fold similar to known kinetochore-binding domains.
• Mad1 CTD contributes to, but is not solely responsible for, kinetochore localization.
• Bub1 was identified as a key receptor for Mad1 CTD-mediated kinetochore targeting.

Conclusions:

• Mad1 CTD is a critical component of an extensive kinetochore-binding interface.
• The findings rationalize the dynamic and graded localization of Mad1 at kinetochores during checkpoint signaling.
• This work provides insights into the regulation of chromosome segregation and aneuploidy prevention.