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Updated: Jun 22, 2025

15N CPMG Relaxation Dispersion for the Investigation of Protein Conformational Dynamics on the µs-ms Timescale
Published on: April 19, 2021
Parsing Dynamics of Protein Backbone NH and Side-Chain Methyl Groups using Molecular Dynamics Simulations
Nooriel E Banayan1, Andrew Hsu2, John F Hunt1
1Department of Biological Sciences, Columbia University, 3000 Broadway, New York, New York 10027, United States.
Molecular dynamics simulations and NMR experiments reveal protein dynamics. Optimized simulations accurately predict generalized order parameters for Escherichia coli ribonuclease HI, enhancing our understanding of enzyme flexibility.
Area of Science:
- Biophysics
- Computational Biology
- Structural Biology
Background:
- Protein conformational dynamics are crucial for biological function.
- Nuclear Magnetic Resonance (NMR) spectroscopy and molecular dynamics (MD) simulations offer complementary views of these dynamics.
- Generalized order parameters quantify molecular motion and flexibility.
Purpose of the Study:
- To compare generalized order parameters for Escherichia coli ribonuclease HI (RNH) derived from extensive microsecond MD simulations with experimental NMR data.
- To evaluate the accuracy of OPLS4 and AMBER-FF19SB force fields in reproducing experimental RNH dynamics.
- To analyze the contributions of backbone and side-chain motions to overall protein flexibility.
Main Methods:
- Performed 2-microsecond MD simulations of RNH using OPLS4 and AMBER-FF19SB force fields.
- Calculated backbone NH and side-chain methyl group generalized order parameters (S^2 and S_axis^2) from simulation trajectories.
- Compared simulated order parameters with experimental values obtained from 15N and 13CH2D spin relaxation measurements.
- Averaged simulated order parameters over 50 ns blocks to optimize agreement with experimental data.
Main Results:
- Optimal agreement between simulated and experimental generalized order parameters was achieved by averaging over 50 ns blocks.
- Median absolute deviations (MAD) between simulated and experimental S^2 (NH) were 0.030 (OPLS4) and 0.041 (AMBER-FF19SB).
- MAD for S_axis^2 (CH3) were 0.061 (OPLS4) and 0.078 (AMBER-FF19SB), indicating good agreement.
- Backbone and side-chain fluctuations showed little correlation; within-rotamer fluctuations were limited and uniform.
Conclusions:
- MD simulations, particularly when averaged over appropriate timescales, can accurately reproduce experimental NMR-derived generalized order parameters for protein dynamics.
- The OPLS4 and AMBER-FF19SB force fields provide reliable descriptions of RNH conformational dynamics.
- Side-chain flexibility, indicated by low S_axis^2 values, is primarily driven by transitions between rotamers, often enhanced by local backbone flexibility.
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