Book of Abstracts: Albany 2007
June 19-23 2007
Structural basis of restoring DNA binding activity to mutant p53 by a second-site suppressor mutation
The tumor-suppressor protein p53 is mutated in more than 50% of invasive cancers. The DNA binding core domain of p53 is the target for nearly 96% of the known tumorigenic mutations. About 30% of the mutations are found in six major ?hotspots? codons (R175, G245, R248, R249, R273, and R282).
To gain structural insights into the deleterious effects of such mutations and their rescue by suppressor mutations, we determined the high-resolution crystal structures of the p53 core domain incorporating the ?hotspot? mutation R249S, the doubly-mutated core domain incorporating R249S and a second-site suppressor mutation H168R (referred to as R249S-H168R), and the complex of R249S-H168R with its DNA binding site. The crystal structures show that the overall fold of the mutated proteins is similar to that of the wild-type (wt) protein. However, the region in the vicinity of the mutation site S249 in the single mutant displays major conformational changes owing to the loss of salt bridges and hydrogen bonds formed by R249 in the wt protein. As a consequence, the protein surface that is critical to the stability and integrity of functional p53-DNA complexes, through protein-protein and protein-DNA interactions, is largely distorted resulting in a drastic reduction of the protein's DNA binding affinity. The conformation of this region is restored in R249S-H168R by the introduction of alternative interactions via R168, and is further stabilized in its complex with DNA. These findings provide a structural framework for understanding dysfunction of p53 as a result of an oncogenic mutation, the rescue of the protein?s activity by a second-site suppressor mutation and its additional stabilization by the DNA target. The acquired structural data may help in rational drug design aimed at restoring wild-type activity to aberrant p53 proteins.
Department of Structural Biology,