Resolving distance variations by single-molecule FRET and EPR spectroscopy using rotamer libraries

Area of Science:

• Biophysics
• Structural Biology
• Biochemistry

Background:

• Förster resonance energy transfer (FRET) and electron paramagnetic resonance (EPR) are complementary spectroscopic techniques used for nanometer-scale distance measurements.
• These methods are crucial for studying the conformations and dynamics of biological macromolecules through site-directed labeling.
• Current limitations include the lack of a common modeling framework for combined FRET and EPR data analysis.

Purpose of the Study:

• To develop a systematic analysis approach for integrating FRET and EPR data.
• To establish a common modeling framework for predicting distance distributions between labels.
• To enable more accurate integrative structural modeling of biological macromolecules.

Main Methods:

• Utilized rotamer libraries for both FRET and EPR labels to predict distance distributions from structural models.
• Incorporated diffusional averaging to account for fluorophore dynamics within distance distributions.
• Benchmarked the methodology using surface-exposed sites in a structured protein domain.

Main Results:

• Demonstrated a systematic analysis approach for combined FRET and EPR data.
• Achieved quantitative agreement between experimental and simulated transfer efficiencies (within ±0.045).
• Resolved distance differences as small as approximately 0.25 nm for both techniques.

Conclusions:

• Rotamer library analysis provides a coherent framework for treating FRET and EPR experimental data.
• This approach facilitates integrative structural modeling of macromolecular conformations and dynamics.
• Enables enhanced understanding of biological macromolecules by combining complementary spectroscopic techniques.