Protein thermal stability: insights from atomic displacement parameters (B values).

Area of Science:

• Structural biology
• Biophysics
• Protein science

Background:

• Thermophilic proteins exhibit enhanced thermal stability compared to mesophilic proteins.
• This stability is often attributed to better-packed interiors and reduced flexibility.
• Understanding these differences is crucial for protein engineering and biotechnology.

Purpose of the Study:

• To analyze B values (related to atomic flexibility) from X-ray crystal structures of mesophilic and thermophilic proteins.
• To investigate the relationship between B values, amino acid composition, and protein dynamics.
• To identify factors contributing to the thermal stability of thermophilic proteins.

Main Methods:

• Analysis of normalized B values (B' factors) from high-resolution X-ray crystal structures.
• Examination of B value distributions, amino acid composition in flexible regions, and B value variation with radius of gyration.
• Assessment of B value dispersion around Calpha atoms.

Main Results:

• Serine (Ser) and Threonine (Thr) exhibit reduced flexibility in thermophiles compared to mesophiles.
• Thermophilic proteins show a higher proportion of Glutamic acid (Glu) and Lysine (Lys) in flexible regions, with lower proportions of Ser and Thr.
• The dispersion of B values around Calpha atoms is comparable between mesophilic and thermophilic proteins.

Conclusions:

• Differences in B value distributions and amino acid composition suggest distinct dynamics between thermophilic and mesophilic proteins.
• These findings provide a basis for predicting amino acid substitutions that can modulate protein thermal stability.
• The study highlights the role of specific amino acids in the adaptation of proteins to extreme environments.