Probing the dynamic properties of two sites simultaneously in a protein-protein interaction process: a SDSL-EPR study

Area of Science:

• Biophysics
• Structural Biology
• Biochemistry

Background:

• Protein flexibility is crucial for molecular processes like protein-protein interactions.
• Understanding structural changes during these interactions is vital.
• Site-Directed Spin Labeling (SDSL) coupled with Electron Paramagnetic Resonance (EPR) spectroscopy is a key technique for monitoring protein structural modifications.

Purpose of the Study:

• To develop a method for simultaneously monitoring structural changes in two different protein regions or partners during interaction.
• To overcome the limitation of overlapping EPR signatures from conventional spin labels.

Main Methods:

• Utilized two spin labels with distinct EPR signatures: maleimido-proxyl (P) and a novel β-phosphorylated (PP) nitroxide.
• Applied these dual labels to a model system: a disordered protein undergoing induced α-helical folding upon binding to its partner.
• Analyzed the EPR spectrum of a mixture of labeled interacting proteins.

Main Results:

• Successfully demonstrated the simultaneous tracking of structural changes using two different spin labels (P and PP) in a single experiment.
• The EPR spectrum of the mixed labeled proteins provided insights into the structural modifications occurring during the protein-protein interaction.
• The β-phosphorylated (PP) nitroxide label provides a distinct 6-line spectrum, differentiating it from the standard 3-line spectrum of maleimido-proxyl (P).

Conclusions:

• This dual-labeling approach significantly advances SDSL-EPR capabilities for studying complex molecular interactions.
• It enables simultaneous monitoring of structural dynamics in multiple protein sites or partners within a single experiment.
• This method offers a powerful new tool for investigating protein flexibility and interaction-induced structural changes.