Ultracompact states of native proteins

Area of Science:

• Structural Biology
• Biophysics
• Crystallography

Background:

• Protein structure and dynamics are influenced by experimental conditions, including temperature.
• The radius of gyration (Rg) is a measure of protein size and compaction.

Purpose of the Study:

• To investigate the effect of data collection temperature on protein intramolecular distances and compaction.
• To identify and characterize instances of extreme protein compaction (ultracompaction).

Main Methods:

• Statistical analysis of approximately 20,000 X-ray crystal structures.
• Comparison of protein radius of gyration (Rg) at cryogenic (≤160K) versus moderate (≥240K) temperatures.
• Detailed structural analysis of ultracompact protein states.

Main Results:

• Cryogenic temperatures significantly reduce protein Rg compared to moderate temperatures.
• Identified 'ultracompact' structures with Rg smaller than expected even at cryogenic temperatures.
• Ultracompaction involves inward atomic displacement, shorter van der Waals and hydrogen bonds, and increased van der Waals contacts.

Conclusions:

• Temperature during data collection critically affects observed protein dimensions.
• Ultracompaction represents a distinct structural state with altered atomic interactions.
• The causes and implications of ultracompaction warrant further investigation.