Direct Determination of Protein Rotational Diffusion Tensors and Generalized Order Parameters from Multifield ¹⁵N NMR...

Area of Science:

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

Background:

• NMR relaxation of backbone amide 15N spins is crucial for characterizing protein dynamics.
• Model selection in dynamic process analysis, like the model-free formalism, complicates NMR applications.
• Chemical exchange significantly impacts transverse relaxation rate (R2), confounding interpretations of 15N spin relaxation data.

Purpose of the Study:

• To develop robust approaches for detecting and removing chemical exchange contributions to R2 using multi-field NMR relaxation data.
• To determine local isotropic rotational correlation times and generalized order parameters without model selection.
• To recursively determine the overall rotational diffusion tensor by maximizing local correlation times.

Main Methods:

• Acquisition of 15N spin relaxation data at three or more static magnetic fields.
• Application of novel methods to separate chemical exchange from R2.
• Recursive maximization of local isotropic rotational correlation times for diffusion tensor determination.

Main Results:

• Successful detection and removal of chemical exchange contributions to R2.
• Determination of local isotropic rotational correlation times and generalized order parameters for individual 15N sites.
• Accurate determination of the overall rotational diffusion tensor for Escherichia coli ribonuclease HI.

Conclusions:

• The developed methods provide a robust way to analyze protein dynamics using NMR spin relaxation.
• These approaches facilitate the determination of key dynamic parameters: rotational diffusion tensor, generalized order parameters, and chemical exchange constants.
• The study broadens the applicability and scope of NMR spin relaxation methods for characterizing protein dynamics.