Probing surface accessibility of proteins using paramagnetic relaxation in solid-state NMR spectroscopy

Area of Science:

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

Background:

• Paramagnetic Relaxation Enhancement (PRE) is a technique to accelerate NMR data acquisition.
• It functions by reducing the longitudinal proton relaxation time T(1) in solid-state samples.
• Understanding site-specific relaxation is crucial for protein structure determination.

Purpose of the Study:

• To investigate the mechanisms of site-specific relaxation induced by paramagnetic compounds in protein samples.
• To differentiate between paramagnetic relaxation and intrinsic protein dynamics.
• To explore the role of hydroxyl groups and water molecules in mediating PRE.

Main Methods:

• Utilized microcrystalline protein samples of the alpha-spectrin SH3 domain.
• Employed perdeuterated samples in a 90% D(2)O buffer to prevent spin diffusion.
• Compared (1)H T(1) relaxation times with varying concentrations of Cu(II)(edta) chelate.

Main Results:

• Paramagnetic compounds induce site-specific relaxation dependent on amide proton surface accessibility.
• Hydroxyl groups and diffusing water molecules can mediate relaxation transfer.
• Efficient difference PRE was observed in flexible protein regions.

Conclusions:

• PRE can be modulated by surface accessibility, hydroxyl groups, and water diffusion.
• This technique allows for site-specific relaxation analysis, aiding in structural studies.
• Deuteration is essential for achieving site-specific resolution in PRE experiments.