Molecular Structure Refinement Based on Residual Dipolar Couplings: A Comparison of the Molecular Rotational-Sampling...

Area of Science:

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Structural Biology
• Computational Chemistry

Background:

• Residual dipolar couplings (RDCs) provide valuable structural information in NMR experiments.
• Calculating RDCs typically assumes a rigid molecule and uses an alignment tensor (AT) to model anisotropic motion.
• This AT approach relies on assumptions of decoupled rotational and internal molecular motions.

Purpose of the Study:

• To investigate the validity of the alignment tensor (AT) approach for calculating RDCs.
• To assess the impact of molecular flexibility on the accuracy of the AT method.
• To compare the AT approach with motion sampling methods for structure refinement.

Main Methods:

• Simulated anisotropic molecular orientation distributions using orientation-biasing forces.
• Calculated RDCs from simulated distributions and used them as target values.
• Applied AT-based RDC refinement and motion sampling methods to assess accuracy.

Main Results:

• The AT approach accurately reproduced target RDCs for a rigid molecule model.
• The AT approach failed to reproduce target RDCs and orientation distributions for a flexible molecule model.
• Motion sampling methods showed better accuracy in reproducing target RDCs and distributions.

Conclusions:

• The AT approach is suitable for rigid molecules but not recommended for flexible biomolecules.
• Accurate molecular structure determination using RDCs requires accounting for both rotational and internal motions.
• Motion sampling methods are superior for structure refinement of flexible molecules based on RDCs.