Structural Basis for the Phase Separation of the Chromosome Passenger Complex.

Area of Science:

• Cellular Biology
• Biochemistry
• Structural Biology

Background:

• Membraneless cellular compartments form via phase separation, a poorly understood process.
• The chromosome passenger complex (CPC) is crucial for mitosis and forms a chromatin body.
• Clarifying the biogenesis of these compartments is a major biological challenge.

Approach:

• Investigated the chromosome passenger complex (CPC) subunits (INCENP, Survivin, Borealin) involved in phase separation.
• Utilized hydrogen/deuterium-exchange mass spectrometry (HXMS) to identify contact regions during droplet formation.
• Employed mutagenesis to probe the role of electrostatic interactions in liquid-liquid demixing.

Key Points:

• Identified specific contact regions within the CPC heterotrimer that mediate phase separation.
• These contact regions align with interfaces observed in the CPC crystal lattice.
• Electrostatic interactions play a significant role, being both breakable and reversible via mutagenesis.

Conclusions:

• Provides structural insights into the interactions driving liquid-liquid demixing of the CPC.
• Demonstrates the utility of HXMS for defining the structural basis of phase separation.
• Advances understanding of the physical principles governing membraneless organelle formation.