1CPN: A coarse-grained multi-scale model of chromatin

Area of Science:

• Epigenetics and Computational Biology
• Molecular Biophysics
• Genomics and Structural Biology

Background:

• Understanding how histone modifications impact eukaryotic genome 3D structure and gene expression is a key challenge in epigenetics.
• Existing computational tools lack the ability to mechanistically link molecular histone information to large-scale genome structure.
• The vast length scales involved, from angstroms for histone modifications to micrometers for genome structure, pose significant computational hurdles.

Purpose of the Study:

• To present a novel molecular model of chromatin, termed 1CPN, that bridges molecular details of histones to large-scale genome structure.
• To provide a computational tool capable of simulating kilobase-scale genomic DNA with detailed physical insights.
• To investigate the influence of linker DNA characteristics on chromatin assembly free energies.

Main Methods:

• Developed the 1CPN model using a multiscale approach, mapping free energies from a validated nucleosome model onto a coarse-grained topology.
• Incorporated detailed nucleosome physics, including histone modifications and DNA sequence, into the coarse-grained model.
• Implemented the 1CPN model within the LAMMPS simulation package for efficient, kilobase-scale simulations.

Main Results:

• The 1CPN model accurately reproduces the free energies and dynamics of single nucleosomes and short chromatin fibers.
• Demonstrated compatibility of the 1CPN model with existing linker histone models.
• Showed that chromatin assembly free energies are significantly dependent on linker DNA length, pitch, and sequence.

Conclusions:

• The 1CPN model offers a powerful new tool for studying the physical underpinnings of genome structure and epigenetic regulation.
• This model facilitates mechanistic investigations into how molecular-level chromatin features dictate large-scale genome organization.
• The 1CPN model is freely available, promoting further research in epigenetics and computational structural biology.