p53, the Cellular Gatekeeper for Growth and Division

MDM2 binds the p53 tumor suppressor protein with high affinity and negatively modulates its transcriptional activity and stability. Overexpression of MDM2, found in many human tumors, effectively impairs p53 function. Inhibition of MDM2-p53 interaction can stabilize p53 and may offer a novel strategy for cancer therapy. Here, we identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes. These compounds bind MDM2 in the p53-binding pocket and activate the p53 pathway in cancer cells, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts in nude mice.

https://science.sciencemag.org/content/sci/303/5659/844.full.pdf

In vivo activation of the p53 pathway by small-molecule antagonists of MDM2.

Intrinsically unstructured proteins: re-assessing the protein structure-function paradigm.

As the tale of p53 unfolds, it becomes ever more intriguing. Although our understanding of the critical and complex roles played by p53 is progressing rapidly, new findings continue to pose new paradoxes. Here we present some of these recent advances in p53 research and discuss how they either shed light on or add to the complexities of p53. Therefore, we only briefly summarize some of the key developments leading to our current state of knowledge. For further information, the reader is referred to several excellent reviews that have focused on p53 research (see Donehower and Bradley 1993; Levine 1993; Greenblatt et al. 1994; Oren 1994; Prives 1994; Kinzler and Vogelstein 1996).

/pdf/p53-puzzle-and-paradigm-fhbzz71yci.pdf

p53: puzzle and paradigm.

DNA Damage-Induced Phosphorylation of p53 Alleviates Inhibition by MDM2

Mutations in the p53 tumor suppressor are the most frequently observed genetic alterations in human cancer. The majority of the mutations occur in the core domain which contains the sequence-specific DNA binding activity of the p53 protein (residues 102-292), and they result in loss of DNA binding. The crystal structure of a complex containing the core domain of human p53 and a DNA binding site has been determined at 2.2 angstroms resolution and refined to a crystallographic R factor of 20.5 percent. The core domain structure consists of a beta sandwich that serves as a scaffold for two large loops and a loop-sheet-helix motif. The two loops, which are held together in part by a tetrahedrally coordinated zinc atom, and the loop-sheet-helix motif form the DNA binding surface of p53. Residues from the loop-sheet-helix motif interact in the major groove of the DNA, while an arginine from one of the two large loops interacts in the minor groove. The loops and the loop-sheet-helix motif consist of the conserved regions of the core domain and contain the majority of the p53 mutations identified in tumors. The structure supports the hypothesis that DNA binding is critical for the biological activity of p53, and provides a framework for understanding how mutations inactivate it.

https://science.sciencemag.org/content/sci/265/5170/346.full.pdf

Crystal structure of a p53 tumor suppressor-DNA complex: Understanding tumorigenic mutations

The MDM2 oncoprotein is a cellular inhibitor of the p53 tumor suppressor in that it can bind the transactivation domain of p53 and downregulate its ability to activate transcription. In certain cancers, MDM2 amplification is a common event and contributes to the inactivation of p53. The crystal structure of the 109-residue amino-terminal domain of MDM2 bound to a 15-residue transactivation domain peptide of p53 revealed that MDM2 has a deep hydrophobic cleft on which the p53 peptide binds as an amphipathic alpha helix. The interface relies on the steric complementarity between the MDM2 cleft and the hydrophobic face of the p53 alpha helix and, in particular, on a triad of p53 amino acids-Phe19, Trp23, and Leu26-which insert deep into the MDM2 cleft. These same p53 residues are also involved in transactivation, supporting the hypothesis that MDM2 inactivates p53 by concealing its transactivation domain. The structure also suggests that the amphipathic alpha helix may be a common structural motif in the binding of a diverse family of transactivation factors to the TATA-binding protein-associated factors.

https://science.sciencemag.org/content/sci/274/5289/948.full.pdf

Structure of the MDM2 oncoprotein bound to the p53 tumor suppressor transactivation domain.

Mutations in the p53 tumor suppressor are among the most frequently observed genetic alterations in human cancer and map to the 200-amino acid core domain of the protein. The core domain contains the sequence-specific DNA binding activity and the in vitro 53BP2 protein binding activity of p53. The crystal structure of the p53 core domain bound to the 53BP2 protein, which contains an SH3 (Src homology 3) domain and four ankyrin repeats, revealed that (i) the SH3 domain binds the L3 loop of p53 in a manner distinct from that of previously characterized SH3-polyproline peptide complexes, and (ii) an ankyrin repeat, which forms an L-shaped structure consisting of a β hairpin and two α helices, binds the L2 loop of p53. The structure of the complex shows that the 53BP2 binding site on the p53 core domain consists of evolutionarily conserved regions that are frequently mutated in cancer and that it overlaps the site of DNA binding. The six most frequently observed p53 mutations disrupt 53BP2 binding in vitro. The structure provides evidence that the 53BP2-p53 complex forms in vivo and may have a critical role in the p53 pathway of tumor suppression.

https://science.sciencemag.org/content/sci/274/5289/1001.full.pdf

Structure of the p53 tumor suppressor bound to the ankyrin and SH3 domains of 53BP2.

The p53 protein is a tetrameric transcription factor that plays a central role in the prevention of neoplastic transformation. Oligomerization appears to be essential for the tumor suppressing activity of p53 because oligomerization-deficient p53 mutants cannot suppress the growth of carcinoma cell lines. The crystal structure of the tetramerization domain of p53 (residues 325 to 356) was determined at 1.7 angstrom resolution and refined to a crystallographic R factor of 19.2 percent. The monomer, which consists of a beta strand and an alpha helix, associates with a second monomer across an antiparallel beta sheet and an antiparallel helix-helix interface to form a dimer. Two of these dimers associate across a second and distinct parallel helix-helix interface to form the tetramer.

https://science.sciencemag.org/content/sci/267/5203/1498.full.pdf

Svetlana Gorina

Papers

Crystal structure of a p53 tumor suppressor-DNA complex: Understanding tumorigenic mutations

Structure of the MDM2 oncoprotein bound to the p53 tumor suppressor transactivation domain.

Structure of the p53 tumor suppressor bound to the ankyrin and SH3 domains of 53BP2.

Crystal Structure of the Tetramerization Domain of the p53 Tumor Suppressor at 1.7 Angstroms