Quantifying Protein Electrostatic Interactions in Cells by Nuclear Magnetic Resonance Spectroscopy

Area of Science:

• Biochemistry
• Biophysics
• Molecular Biology

Background:

• Proteins function within complex cellular environments.
• Understanding how the cellular milieu affects protein interactions is crucial for elucidating protein function.
• Electrostatic interactions are fundamental to protein structure and function.

Purpose of the Study:

• To investigate the impact of the cellular environment on protein electrostatic interactions.
• To quantify changes in electrostatic interactions using in-cell spectroscopy.
• To identify the factors responsible for modulating these interactions within cells.

Main Methods:

• Utilized in-cell nuclear magnetic resonance (NMR) spectroscopy.
• Introduced eight specific charge pairs into the protein GB3.
• Compared electrostatic interactions of these charge pairs in a cellular environment versus a buffer solution.

Main Results:

• Five out of eight introduced charge pairs showed no significant change in electrostatic interaction strength within cells.
• Three charge pairs exhibited weakened electrostatic interactions, with reductions exceeding 70% compared to buffer conditions.
• Transfer free energy was identified as the primary contributor to the observed modulation of electrostatic interactions.

Conclusions:

• The cellular environment significantly modulates protein electrostatic interactions.
• Transfer free energy, especially from the unfolded state, plays a key role in this modulation.
• Direct in-cell studies are essential for understanding protein interactions and functions accurately within their native environment.