Rigid protein motion as a model for crystallographic temperature factors

Area of Science:

• Structural Biology
• Biophysics
• Crystallography

Background:

• Crystallographic temperature factors (B-factors) describe atomic motion in proteins.
• Modeling these factors is crucial for understanding protein dynamics and refining structural models.

Purpose of the Study:

• To assess the efficacy of rigid molecule librations in modeling protein crystallographic temperature factor profiles.
• To explore the utility of a simplified rigid body model for X-ray structure refinement.

Main Methods:

• Applied a 10-parameter rigid body model to diverse protein structures (hemagglutinin, glutathione reductase, myohemerythrin, myoglobin, streptavidin).
• Analyzed the correlation between deviations in rigid molecule vs. atomic temperature factors and structural model quality.
• Investigated domain-based rigid body refinement for high-resolution structures.

Main Results:

• The rigid body model qualitatively reproduced patterns in isotropic backbone mean-square displacements for all tested proteins.
• Significant deviations correlated with regions of unsatisfactory or incorrect structural models.
• Treating domains as independent rigid bodies improved results for high-resolution glutathione reductase.

Conclusions:

• Rigid body refinement offers a parameter-efficient method for refining temperature factors and evaluating protein models.
• The success of the rigid protein model suggests its results should inform interpretations of crystallographic thermal parameters.