KNL1 Binding to PP1 and Microtubules Is Mutually Exclusive

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The kinetochore scaffold 1 (KNL1) protein is crucial for the spindle assembly checkpoint (SAC), which ensures accurate chromosome segregation.
• Microtubules and protein phosphatase 1 (PP1) are known regulators of KNL1 and the SAC, but their interaction mechanism was unclear.

Purpose of the Study:

• To elucidate the molecular mechanism by which KNL1 interacts with both PP1 and microtubules.
• To understand how these interactions contribute to the regulation of the spindle assembly checkpoint (SAC).

Main Methods:

• X-ray crystallography
• Nuclear magnetic resonance (NMR) spectroscopy
• Biochemical assays
• Co-sedimentation assays

Main Results:

• PP1 and microtubules bind to overlapping sites on the N-terminal domain of KNL1.
• Aurora B kinase phosphorylation disrupts KNL1 complexes in distinct patterns.
• Microtubule and PP1 binding to KNL1 are mutually exclusive events.

Conclusions:

• The study reveals a competitive binding mechanism between PP1 and microtubules at KNL1.
• This mutual exclusivity, particularly the preferential formation of the KNL1:PP1 holoenzyme, is critical for SAC regulation.
• Findings provide new insights into the intricate molecular orchestration of chromosome segregation.