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Intramolecular dielectric screening in proteins.
T Simonson1, D Perahia, G Bricogne
1Laboratoire pour l'Utilisation du Rayonnement Electromagnétique CNRS, CEA, MEN, Université de Paris-Sud, Orsay, France.
Journal of Molecular Biology
|April 20, 1991
Summary
This study reveals how proteins shield charges at a microscopic level. Variations in dynamic dipolar relaxation, not uniform electronic polarizability, are key to protein function and binding interactions.
Area of Science:
- Biophysics
- Computational Chemistry
- Protein Dynamics
Background:
- Proteins interact with charged species, necessitating efficient charge screening mechanisms.
- Understanding these mechanisms is crucial for deciphering protein function and biological processes.
Purpose of the Study:
- To investigate the microscopic origins of charge screening in proteins.
- To introduce and analyze the generalized susceptibility of proteins.
- To test the hypothesis that spatial variations in susceptibility correlate with functional activity.
Main Methods:
- Developed a model representing protein dielectric properties using atomic polarizabilities and normal mode dynamics.
- Calculated the generalized susceptibility in closed form.
- Applied the model to alpha-helices and cytochrome c, comparing results with continuum models.
Main Results:
- Electronic contributions to susceptibility are uniform, while dynamic dipolar relaxation contributions vary spatially within proteins.
- Spatial variation in intramolecular screening was shown to influence the binding of charged ligands to alpha-helices.
- Analyzed the dielectric susceptibility of cytochrome c, estimating the contribution of atomic position relaxation to activation free energy for electron transfer.
Conclusions:
- The spatial variation of dynamic dipolar relaxation is a significant factor in protein function, particularly in interactions with charged species.
- The developed model provides a quantitative link between protein dielectric properties and functional activity.
- This approach offers insights into charge screening mechanisms and their role in biological processes like electron transfer.