Accurate Electron-Nucleus Distances from Paramagnetic Relaxation Enhancements

Area of Science:

• Structural Biology
• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Biophysics

Background:

• Paramagnetic Relaxation Enhancements (PREs) in 1H NMR spectra are crucial for determining long-range distances in proteins.
• Quantitative interpretation of PREs is often hindered by non-specific intermolecular effects.
• Accurate, calibration-free distance measurements remain a challenge in protein structural studies.

Purpose of the Study:

• To develop a method for accurate, calibration-free distance measurements using PREs.
• To overcome limitations imposed by non-specific intermolecular PREs.
• To leverage lanthanides with anisotropic magnetic susceptibilities for improved quantitative analysis.

Main Methods:

• Utilized lanthanides with anisotropic magnetic susceptibilities to generate PREs.
• Measured relaxation rates in both paramagnetic and diamagnetic states within a single protein sample.
• Employed pseudocontact shifts to simultaneously label the protein with paramagnetic and diamagnetic lanthanide ions.

Main Results:

• Demonstrated that PREs from anisotropic lanthanides enable accurate, calibration-free distance measurements.
• Successfully subtracted non-specific intermolecular PREs by calculating the difference in nuclear relaxation rates.
• Achieved unprecedented accuracy in intramolecular PRE measurements for calbindin D9k using erbium, yielding distance predictions with <0.9 Å RMSD.

Conclusions:

• Lanthanides with anisotropic magnetic susceptibilities provide a robust route to accurate, calibration-free distance measurements in proteins.
• The developed method effectively mitigates non-specific intermolecular PREs, enhancing quantitative interpretation.
• This technique offers a powerful tool for precise long-range distance determination in structural biology.