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A self-consistent, microenvironment modulated screened coulomb potential approximation to calculate pH-dependent
1Department of Physiology and Biophysics, Mount Sinai School of Medicine, CUNY, New York, New York 10029, USA. mehler@inka.mssm.edu
Biophysical Journal
|July 2, 1999
Summary
This study introduces a new method to calculate protein pKa shifts by analyzing residue microenvironments. This approach accurately predicts shifts based on local hydrophobicity, improving electrostatic calculations in proteins.
Area of Science:
- Biophysics
- Computational Biology
- Protein Chemistry
Background:
- Calculating pH-dependent electrostatic effects in proteins, particularly pKa shifts, is complex.
- Aberrant pKa shifts are often attributed to unique residue microenvironments.
- Existing models may not fully capture the dielectric properties of these microenvironments.
Purpose of the Study:
- To develop and validate an improved computational approach for calculating pH-dependent electrostatic effects in proteins.
- To characterize protein microenvironments based on local hydrophobicity/hydrophilicity.
- To demonstrate that microenvironmental properties are key determinants of pKa shifts.
Main Methods:
- Utilized sigmoidally screened Coulomb potentials (SCP) for electrostatic calculations.
- Developed a method to quantitatively characterize local hydrophobicity/hydrophilicity around protein residues.
- Integrated microenvironmental characterization into the SCP algorithm.
Main Results:
- The new approach accurately predicted over 100 measured pKa values across seven proteins with a root mean square deviation of 0.5.
- Successfully resolved previously intractable problems in pKa calculation, such as divergent shifts in hen egg white lysozyme.
- Demonstrated that local hydrophobicity/hydrophilicity dictates dielectric screening, explaining divergent pKa shifts for buried residues (Glu-35 vs. Asp-66).
- The computational speed of the SCP formulation was conserved.
Conclusions:
- Local microenvironmental properties, specifically hydrophobicity/hydrophilicity, are critical for accurate pKa shift calculations.
- The improved SCP approach provides a physical basis for understanding and predicting pKa variations.
- The method's efficiency and accuracy allow for the analysis of different protein conformations and their relevance to solution structures.