Probing electric fields in proteins in solution by NMR spectroscopy

Area of Science:

• Biophysics
• Structural Biology
• Protein NMR Spectroscopy

Background:

• Electric fields are crucial for protein function, influencing processes like catalysis and binding.
• Understanding the precise electric field distribution within proteins is essential for deciphering their mechanisms.
• Nuclear magnetic resonance (NMR) chemical shifts are sensitive to the local electronic environment.

Purpose of the Study:

• To develop and validate a method for probing electric field changes at specific sites within proteins.
• To investigate the impact of introduced charges on protein electric fields.
• To explore the utility of NMR chemical shifts in characterizing protein electrostatics.

Main Methods:

• Utilized amide (1)H and (15)N NMR chemical shifts to detect electric field variations.
• Introduced controlled charge perturbations in the blue copper protein plastocyanin.
• Employed side-chain protonation and metal ion substitution to alter protein charges.

Main Results:

• Observed significant chemical shift perturbations (CSPs) correlated with introduced charges.
• Demonstrated that CSPs primarily arise from long-range electric field effects.
• Quantified the influence of electric charge on NMR chemical shifts within the protein.

Conclusions:

• The developed NMR method effectively probes localized electric fields in proteins.
• CSPs provide a sensitive measure of electrostatic interactions and charge distribution.
• This approach can be used to estimate dielectric properties and nuclear shielding polarizability within proteins.