DNA-protamine condensates under low salt conditions: molecular dynamics simulation with a simple coarse-grained model...

Area of Science:

• Biophysics
• Molecular Biology
• Nanotechnology

Background:

• Protamine protein is essential for DNA condensation in sperm and in nanoparticle formulations for gene therapy and mRNA vaccines.
• The precise mechanisms of protamine-mediated DNA condensation, particularly under low salt conditions, remain poorly understood.
• Electrostatic interactions are known to be dominant under low salt conditions, influencing protamine-DNA complex formation.

Purpose of the Study:

• To investigate the role of electrostatic interactions in protamine-controlled reversible DNA condensation.
• To develop a simplified coarse-grained model for large-scale simulations of DNA-protamine systems.
• To elucidate the nanoscale mechanisms of DNA bundle formation and the influence of protamine length on condensate properties.

Main Methods:

• Devised a coarse-grained bead-spring model focusing on linear charge density of protamine and DNA.
• Employed effective pair potential calculations and large-scale molecular dynamics simulations.
• Simulated DNA phase behavior across a range of protamine concentrations under low salt conditions.

Main Results:

• Reproduced DNA phase behavior, confirming the critical role of electrostatic interactions in condensation.
• Provided a nanoscale picture of DNA bundle formation mediated by a charge disproportionation mechanism.
• Demonstrated that protamine length influences DNA overcharging and condensate redissolution thresholds.

Conclusions:

• Electrostatic interactions are the primary drivers of protamine-mediated DNA condensation.
• Protamine length offers a tunable parameter for designing gene therapy nanoparticles.
• Understanding DNA-protamine condensates provides insights into biomolecular condensates and chromatin organization during spermatogenesis.