Beyond structure: Deciphering site-specific dynamics in proteins from double histidine-based EPR measurements

Area of Science:

• Biophysics
• Structural Biology
• Protein Dynamics

Background:

• Protein dynamics are crucial for function, but measuring site-specific dynamics in large complexes, especially beta-sheets, is challenging.
• Traditional electron paramagnetic resonance (EPR) methods often rely on flexible nitroxide labels, limiting their application for certain protein structures.

Purpose of the Study:

• To develop and apply a novel EPR-based method for measuring site-specific protein dynamics.
• To investigate the dynamics of both alpha-helical and beta-sheet regions within the GB1 protein.
• To expand the capabilities of copper(II)-nitrilotriacetic acid (Cu(II)NTA) EPR for probing protein dynamics beyond distance measurements.

Main Methods:

• Utilized electron paramagnetic resonance (EPR) spectroscopy on the GB1 protein.
• Employed a double Histidine (dHis) motif for site-specific labeling with a Cu(II)-nitrilotriacetic acid (NTA) complex.
• Performed spectral simulations of continuous-wave EPR (CW-EPR) data.
• Complemented experimental EPR data with molecular dynamics (MD) simulations.

Main Results:

• Successfully measured site-specific dynamics across the GB1 protein surface, including alpha-helical and beta-sheet sites.
• CW-EPR spectral simulations revealed unique site-specific fluctuations.
• MD simulations corroborated the dynamics observed via EPR.
• Observed minor variations in gǁ values, potentially indicating differences in coordination geometry or local electrostatics.

Conclusions:

• The Cu(II)NTA-based EPR approach effectively probes site-specific protein dynamics, extending beyond traditional distance measurements.
• This method provides valuable insights into the fluctuations of both helical and sheet secondary structures.
• The findings enhance the utility of EPR spectroscopy for studying complex protein systems.