NMR studies of lysozyme surface accessibility by using different paramagnetic relaxation probes

Area of Science:

• Biochemistry
• Structural Biology
• Biophysical Chemistry

Background:

• Paramagnetic probes are crucial for investigating protein surface accessibility via nuclear magnetic resonance (NMR).
• Existing probes may exhibit charge-dependent interactions, potentially influencing accessibility studies.
• High relaxivity and neutral charge are desirable properties for paramagnetic probes.

Purpose of the Study:

• To introduce and evaluate a novel neutral, bimetallic gadolinium complex, [Gd2(L7)(H2O)2], as a paramagnetic probe for NMR-based protein surface accessibility studies.
• To assess the probe's suitability for systematic investigations by verifying the absence of specific interactions with a model protein.

Main Methods:

• Utilized hen egg white lysozyme as a model system.
• Compared paramagnetic perturbation profiles of 1H-13C HSQC signals using the novel Gd(III) complex and TEMPOL.
• Analyzed differences in probe interactions to infer surface accessibility and dynamics.

Main Results:

• The neutral Gd(III) complex, [Gd2(L7)(H2O)2], showed similar perturbation profiles to TEMPOL, indicating no specific interactions with the lysozyme.
• Strong paramagnetic perturbations were observed for CalphaH groups on convex, surface-exposed regions, attributed to the probe's large size.
• Combined use of probes revealed detailed dynamics of protein surface interactions.

Conclusions:

• The neutral Gd(III) complex is a suitable probe for NMR studies of protein surface accessibility, free from charge-driven artifacts.
• The probe's size influences its interaction with protein surface topography, providing insights into dynamics.
• This approach enhances the understanding of protein surface accessibility and dynamics.