Related Experiment Videos
Reintroducing electrostatics into protein X-ray structure refinement: bulk solvent treated as a dielectric continuum
Luc Moulinier1, David A Case, Thomas Simonson
1Département de Biologie et Génomique Structurales, Institut de Génétique et Biologie Moléculaire et Cellulaire (CNRS), 1 Rue Laurent Fries, 67404 Illkirch-Strasbourg, France.
Acta Crystallographica. Section D, Biological Crystallography
|December 4, 2003
Summary
Incorporating electrostatic and solvation terms into protein X-ray crystallography refinements using the Generalized Born (GB) model yields structures of similar accuracy. Differences in side-chain conformations were observed, particularly for surface residues, suggesting improved precision with the GB model.
Area of Science:
- Structural Biology
- Computational Biology
- Biophysics
Background:
- Protein structure refinement traditionally uses X-ray data and stereochemical restraints.
- Electrostatic and solvation effects are often excluded due to challenges in modeling solvent dielectric screening.
- Implicit solvent models, like the Generalized Born (GB) model, now enable more comprehensive calculations.
Purpose of the Study:
- To investigate if including electrostatic and solvation terms in protein structure refinement improves accuracy or yields different structures of equivalent quality.
- To evaluate the Generalized Born (GB) model for X-ray refinement of protein structures.
Main Methods:
- Applied the Generalized Born (GB) implicit solvent model to X-ray refinements of three protein structures (2.4-3.2 Å resolution).
- Utilized a target function incorporating stereochemistry, van der Waals, Coulomb, solvation interactions, and X-ray pseudo-energy.
- Performed simulated-annealing refinements in torsion-angle space using both conventional and GB target functions.
Main Results:
- Refined structures using the GB model showed comparable accuracy to conventional methods, assessed by free R factor and map/model correlations.
- Approximately 10% of side-chain conformations differed between GB and conventional refinements, with most differences on protein surfaces.
- One case indicated the GB model provided a more realistic estimate of structural precision compared to the conventional method.
Conclusions:
- The Generalized Born (GB) model can be integrated into protein X-ray refinement with comparable accuracy to traditional methods.
- The GB approach reveals subtle differences in side-chain conformations, potentially offering a more nuanced understanding of protein structure precision.
- Further improvements in GB parameterization are expected to enhance the utility of this method in structural biology.