In vitro structure-function analysis of the beta-strand 326-333 of human p53.

The beta-strand 326-333 is a key structural element in the formation of p53 tetramers. To investigate the contribution of its amino acid residues, an alanine scan was performed. The oligomerisation and DNA-binding properties of the mutant proteins were compared with those of wild-type proteins in vitro and analysed on the basis of the crystal structure of the p53 tetramerisation domain at 1.5 A resolution. Two categories of mutant proteins were identified. Phe328Ala, Leu330Ala and Ile332Ala mutant proteins are inactive for DNA binding and oligomerisation, while the Glu326Ala, Tyr327Ala, Thr329Ala, Gln331Ala and Arg333Ala mutant proteins have properties similar to those of wild-type proteins. These results suggest that single mutations within the p53 tetramerisation domain destabilise the structure of the whole protein, inhibiting its DNA-binding activity. Furthermore, the mutation of leucine 330 to alanine within the tetramerisation domain of the Arg175His protein abolishes the dominant negative effect of this mutant. This shows that the beta-strand 326-333 is a key structural element that mediates the dominant negative effect of p53 mutants.