A pH-sensitive, colorful, lanthanide-chelating paramagnetic NMR probe.

Area of Science:

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

Background:

• Paramagnetic lanthanide ions are crucial tools in NMR spectroscopy for characterizing macromolecular structure and dynamics.
• Existing lanthanide-chelating NMR probes have limitations in charge and magnetic properties.

Purpose of the Study:

• To introduce a novel lanthanide-chelating NMR probe, Caged Lanthanide NMR Probe-7 (CLaNP-7).
• To evaluate CLaNP-7's utility in protein structure determination and explore its unique properties compared to previous probes.

Main Methods:

• Development and characterization of the CLaNP-7 probe.
• Attachment of CLaNP-7 to protein surfaces via disulfide bridges.
• NMR spectroscopy to analyze probe effects on spectral parameters and structural restraints.
• Investigation of pH-dependent magnetic susceptibility tensor orientation.

Main Results:

• CLaNP-7 is a rigid, yellow-colored probe with a lower positive charge (+1) than CLaNP-5 (+3), minimizing surface potential changes.
• The probe provides a distinct magnetic susceptibility tensor, enabling dual structural restraints per engineered cysteine pair.
• A pH-dependent orientation of the magnetic susceptibility tensor (pK(a) ≈ 7) was observed, linked to histidine interaction.

Conclusions:

• CLaNP-7 expands the applicability of lanthanide-based NMR probes for macromolecular studies.
• The pH-dependent interaction with histidine residues offers new avenues for probing local protein environments.
• This probe facilitates advanced structural and dynamic characterization of proteins.