Analysis of temperature factor distribution in high-resolution protein structures

Area of Science:

• Structural Biology
• Biophysics
• Computational Biology

Background:

• X-ray crystallography provides atomic-level insights into protein structures.
• Temperature factors (B-values) quantify atomic motion and disorder in protein crystals.
• Variations in B-values across different protein structures are significant.

Purpose of the Study:

• To analyze the frequency distribution of B-values at C-alpha atoms across a large protein dataset.
• To identify characteristic patterns in B-value distributions and their relationship to residue properties.
• To investigate the underlying causes of observed B-value distributions in protein structures.

Main Methods:

• Analysis of B-values from X-ray refinement data of 110 high-resolution protein structures.
• Calculation and statistical analysis of B-value frequency distributions at C-alpha atoms.
• Modeling the distribution as a superposition of Gaussian functions.

Main Results:

• A consistent bimodal distribution of B'-factors (normalized B-values) was observed in all 110 proteins.
• Peaks in the B'-factor distribution were identified at -1.1 and 0.4 (bin size 0.5).
• Lower B'-factors correlated with buried residues, higher B'-factors with exposed residues.
• Amino acid-specific distributions also showed bimodal patterns, influenced by hydrophilicity and rigidity.
• Deviations from random distribution were noted for stretches of high B'-factors, suggesting residue correlation.

Conclusions:

• The bimodal distribution of B'-factors is a characteristic feature of protein structures.
• This distribution reflects the distinct motional properties of buried versus exposed amino acid residues.
• Correlations between sequentially proximal residues likely contribute to the observed bimodal pattern and non-random distributions.