Promiscuous Histone Mis-Assembly Is Actively Prevented by Chaperones.

Area of Science:

• Molecular Biology
• Structural Biology
• Epigenetics

Background:

• Histone proteins organize eukaryotic genetic material.
• Centromere protein A (CENP-A) is a histone H3 variant essential for centromere function and chromosome segregation.
• CENP-A/H4 and H3/H4 dimers share structural similarity despite distinct roles.

Purpose of the Study:

• To characterize the structural dynamics of CENP-A/H4 and H3/H4 dimers.
• To elucidate the role of the chaperone HJURP in CENP-A/H4 stability.
• To investigate the functional impact of specific CENP-A modifications.

Main Methods:

• Dual-resolution molecular dynamics (MD) simulations (explicit-solvent all-atom and coarse-grained).
• Analysis of histone dimer dynamics and flexibility.
• In vivo experiments to assess CENP-A localization.

Main Results:

• H4 histone is more rigid than H3 and CENP-A, acting as a structural element.
• The CENP-A/H4 dimer exhibits greater dynamics than the H3/H4 dimer.
• Holliday Junction Recognition Protein (HJURP) stabilizes CENP-A/H4 via electrostatic interactions.
• A specific CENP-A mutation (S68E) disrupts HJURP binding and centromere localization.

Conclusions:

• The CENP-A/H4 dimer's increased flexibility, compared to H3/H4, is physically explained.
• HJURP acts as both a folding and binding chaperone, stabilizing CENP-A/H4 during deposition.
• HJURP-mediated stabilization and protection of CENP-A/H4 substructures are critical for centromere targeting.