p53 Contains Large Unstructured Regions in its Native State

The human tumor suppressor protein p53 is understood only to some extent on a structural level. We performed a comprehensive biochemical and biophysical structure–function analysis of p53 full-length protein and p53 fragments. The analysis showed that p53 and the fragments investigated form stable functional units. Full-length p53 and the tetrameric fragment N93p53 (residues 93–393) are, however, destabilized significantly compared to the monomeric core domain (residues 94–312) and the monomeric fragment p53C312 (residues 1–312). At the physiological temperature of 37 °C and in the absence of modifications or stabilizing partners, wild-type p53 is more than 50% unfolded correlating with a 75% loss in DNA-binding activity. Furthermore the analysis of CD spectra revealed that full-length p53 contains large unstructured regions in its N and C-terminal parts. Our results indicate that full-length p53 is a modular protein consisting of defined structured and unstructured regions. We propose that p53 belongs to the growing family of loosely folded or partially unstructured native proteins. The lack of a rigid structure combined with the low overall stability may allow the physiological interaction of p53 with a multitude of partner proteins and the regulation of its turnover.