Structure Of P53 Core Domain Research Articles

Structure of the human p53 core domain in the absence of DNA

The tumor suppressor protein p53 plays a key role in cell-cycle regulation by triggering DNA repair, cell-cycle arrest and apoptosis when the appropriate signal is received. p53 has the classic architecture of a transcription factor, with an amino-terminal transactivation domain, a core DNA-binding domain and carboxy-terminal tetramerization and regulatory domains. The crystal structure of the p53 core domain, which includes the amino acids from residue 96 to residue 289, has been determined in the absence of DNA to a resolution of 2.05 A. Crystals grew in a new monoclinic space group (P2(1)), with unit-cell parameters a = 68.91, b = 69.36, c = 84.18 A, beta = 90.11 degrees . The structure was solved by molecular replacement and has been refined to a final R factor of 20.9% (R(free) = 24.6%). The final model contains four molecules in the asymmetric unit with four zinc ions and 389 water molecules. The non-crystallographic tetramers display different protein contacts from those in other p53 crystals, giving rise to the question of how p53 arranges as a tetramer when it binds its target DNA.

High-resolution structure of the p53 core domain: implications for binding small-molecule stabilizing compounds

The p53 transcriptional regulator is the most frequently mutated protein in human cancers and the majority of tumor-derived p53 mutations map to the central DNA-binding core domain, with a subset of these mutations resulting in reduced p53 stability. Here, the 1.55 A crystal structure of the mouse p53 core domain with a molecule of tris(hydroxymethyl)aminomethane (Tris) bound through multiple hydrogen bonds to a region of p53 shown to be important for repair of a subset of tumor-derived p53-stability mutations is reported. Consistent with the hypothesis that Tris binding stabilizes the p53 core domain, equilibrium denaturation experiments are presented that demonstrate that Tris binding increases the thermodynamic stability of the mouse p53 core domain by 3.1 kJ mol(-1) and molecular-dynamic simulations are presented revealing an overall reduction in root-mean-square deviations of the core domain of 0.7 A when Tris is bound. It is also shown that these crystals of the p53 core domain are suitable for the multiple-solvent crystal structure approach to identify other potential binding sites for possible core-domain stabilization compounds. Analysis of the residue-specific temperature factors of the high-resolution core-domain structure, coupled with a comparison with other core-domain structures, also reveals that the L1, H1-S5 and S7-S8 core-domain loops, also shown to mediate various p53 activities, harbor inherent flexibility, suggesting that these regions might be targets for other p53-stabilizing compounds. Together, these studies provide a molecular scaffold for the structure-based design of p53-stabilization compounds for development as possible therapeutic agents.

Solution structure of p53 core domain: Structural basis for its instability

The 25-kDa core domain of the tumor suppressor p53 is inherently unstable and melts at just above body temperature, which makes it susceptible to oncogenic mutations that inactivate it by lowering its stability. We determined its structure in solution using state-of-the-art isotopic labeling techniques and NMR spectroscopy to complement its crystal structure. The structure was very similar to that in the crystal but far more mobile than expected. Importantly, we were able to analyze by NMR the structural environment of several buried polar groups, which indicated structural reasons for the instability. NMR spectroscopy, with its ability to detect protons, located buried hydroxyl and sulfhydryl groups that form suboptimal hydrogen-bond networks. We mutated one such buried pair, Tyr-236 and Thr-253 to Phe-236 and Ile-253 (as found in the paralogs p63 and p73), and stabilized p53 by 1.6 kcal/mol. We also detected differences in the conformation of a mobile loop that might reflect the existence of physiologically relevant alternative conformations. The effects of temperature on the dynamics of aromatic residues indicated that the protein also experiences several dynamic processes that might be related to the presence of alternative hydrogen-bond patterns in the protein interior. p53 appears to have evolved to be dynamic and unstable.