Long-Range Modulations of Electric Fields in Proteins.

Area of Science:

• Biophysics
• Protein Electrostatics
• Surface Science

Background:

• Protein structure and function are critically influenced by electrostatic interactions.
• Previous research primarily focused on local electrostatic effects within proteins.
• The impact of long-range electric fields on proteins, particularly upon surface binding, remains less understood.

Purpose of the Study:

• To investigate the long-range modulation of electric fields in proteins when they bind to charged surfaces.
• To quantify the contributions of different electrostatic effects (surface binding and interface potential drops) to the internal electric field of proteins.
• To establish a method for separating hydrogen-bonding and non-hydrogen-bonding electric field contributions.

Main Methods:

• Utilized cytochrome c (Cytc) variants with nitrile reporters for vibrational Stark effect measurements.
• Employed genetic engineering and chemical modification to incorporate nitrile reporters.
• Performed molecular dynamics (MD) simulations to calculate electric fields and hydrogen bond occupancy.
• Developed a model correlating experimental nitrile stretching frequencies with calculated electric fields.

Main Results:

• Established a reliable method to separate hydrogen-bonding and non-hydrogen-bonding electric field effects in Cytc variants in solution.
• Quantified electric field changes (Δ E_ads and Δ E_int) upon Cytc binding to charged surfaces (gold electrodes with SAMs).
• Found that long-range electrostatic contributions (Δ E_ads and Δ E_int) are comparable in magnitude to the internal non-hydrogen-bonding electric field of unbound Cytc.

Conclusions:

• Long-range electrostatic modulation of protein electric fields by charged surfaces is significant.
• This modulation, encompassing both direct binding and interface potential effects, can influence protein function.
• Findings are relevant for understanding protein interactions with membranes and other proteins.