Ultracompact states of native proteins.

A statistical analysis of circa 20,000 X-ray structures evidenced the effects of temperature of data collection on protein intramolecular distances and degree of compaction. Identical chains with data collected at cryogenic ultralow temperatures (≤160K) showed a radius of gyration (R) significantly smaller than at moderate temperatures (≥240K). Furthermore, the analysis revealed the existence of structures with a R significantly smaller than expected for cryogenic temperatures.