Structural basis for the phase separation of the chromosome passenger complex

Area of Science:

• Biochemistry
• Cell Biology
• Structural Biology

Background:

• Membraneless cellular compartments form through liquid-liquid phase separation (LLPS), a process crucial for cellular organization but poorly understood at a molecular level.
• The chromosome passenger complex (CPC) is a key regulator of mitosis, forming a chromatin body through phase separation.
• Understanding the physical basis of LLPS is a major challenge in modern biology.

Purpose of the Study:

• To elucidate the structural basis of phase separation within the chromosome passenger complex (CPC).
• To identify the specific molecular interactions driving the liquid-liquid demixing of the CPC.
• To validate hydrogen/deuterium exchange mass spectrometry (HXMS) as a method for studying LLPS.

Main Methods:

• Hydrogen/deuterium exchange mass spectrometry (HXMS) was employed to map contact regions within the CPC during droplet formation.
• Mutagenesis studies were used to investigate the role of electrostatic interactions in CPC phase separation.
• Analysis of crystal lattice interfaces was performed for comparison with phase-separated structures.

Main Results:

• Specific contact regions within the INCENP-Survivin-Borealin heterotrimer were identified during CPC droplet formation.
• These contact regions largely overlap with interfaces observed in the CPC crystal lattice.
• Electrostatic interactions were found to be critical for driving CPC liquid-liquid demixing, and these interactions could be modulated by mutagenesis.

Conclusions:

• The study provides detailed structural insights into the molecular interactions governing CPC phase separation.
• Electrostatic interactions play a significant role in the biogenesis of CPC-containing membraneless compartments.
• HXMS is established as a powerful technique for defining the structural underpinnings of biomolecular phase separation.