Model-free extraction of spin label position distributions from pseudocontact shift data

Area of Science:

• Biomolecular NMR Spectroscopy
• Structural Biology
• Paramagnetic Resonance Spectroscopy

Background:

• Paramagnetic tags are crucial for protein and nucleic acid structure determination using NMR and EPR.
• Conformational mobility of these tags introduces uncertainty in structural analyses.
• Current methods, particularly pseudocontact shift (PCS) NMR, often rely on simplified point-center approximations for tag positioning.

Purpose of the Study:

• To develop a novel method for accurately determining the probability distribution of lanthanide tag conformations from PCS NMR data.
• To overcome the limitations of the point paramagnetic center approximation in PCS NMR spectroscopy.
• To enable detailed analysis of biomolecular structure and dynamics at room temperature in solution.

Main Methods:

• Utilized Tikhonov-regularized 3D reconstruction to process PCS NMR data.
• Applied the method to lanthanide-tagged mutants (Tm3+ DOTA-M8) of human carbonic anhydrase II.
• Validated results against established rotamer library and Double Electron-Electron Resonance (DEER) data.

Main Results:

• Successfully extracted detailed probability densities of lanthanide tag conformations.
• Demonstrated good agreement between the new method's results and existing experimental data (rotamer library, DEER).
• Showcased the potential to re-analyze historical PCS NMR data for conformational insights.

Conclusions:

• The developed method provides a robust approach to characterizing paramagnetic tag conformational dynamics in solution.
• This technique significantly enhances the utility of PCS NMR spectroscopy for structural biology.
• It opens new avenues for understanding biomolecular structure and dynamics by leveraging previously underutilized PCS data.