Diffusion and electrophoretic mobility of single-stranded RNA from molecular dynamics simulations.

Area of Science:

• Biophysics
• Computational Chemistry
• Molecular Biology

Background:

• Understanding the hydrodynamic properties of small nucleic acids is crucial for molecular biology and biophysical applications.
• Previous studies have explored RNA behavior, but detailed simulation-based analysis of short RNA homopolymers in explicit solvent remains an area for deeper investigation.

Purpose of the Study:

• To determine the hydrodynamic properties, specifically electrophoretic mobility and diffusion coefficients, of small single-stranded RNA homopolymers (3 and 6 nucleotides) using molecular dynamics simulations.
• To investigate the influence of counterion interactions on these properties and their relationship with the Nernst-Einstein equation.
• To analyze the impact of counterion atmosphere fluctuations on measured diffusion coefficients, particularly in the context of capillary zone electrophoresis.

Main Methods:

• Performing molecular dynamics (MD) simulations of three- and six-nucleotide single-stranded RNA homopolymers in explicit water solvent.
• Calculating diffusion coefficients and electrophoretic mobilities from simulation trajectories.
• Analyzing the role of counterions and their fluctuations in the electrostatic environment surrounding the RNA molecules.
• Comparing simulation results with experimental data and established hydrodynamic theories.

Main Results:

• Electrophoretic mobility of RNA increases with nucleotide chain length, consistent with experimental observations.
• Diffusion coefficients, after corrections for finite-size and solvent viscosity, show good agreement with experimental estimates and hydrodynamic calculations.
• A Nernst-Einstein relationship is observed, indicating that the effective charge of RNA is modulated by bound counterions.
• Counterion atmosphere fluctuations were found to enhance the apparent diffusion of RNA molecules along the electric field direction.

Conclusions:

• The study provides a detailed molecular-level understanding of the hydrodynamic behavior of short RNA molecules in solution.
• Counterion dynamics significantly influence the measured transport properties of RNA, leading to potential discrepancies between simulation and experimental values under specific conditions.
• Findings are relevant for interpreting experimental data from techniques like capillary zone electrophoresis and for designing nucleic acid-based technologies.