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Oligomerization of members of the p53 family of transcription factors (p53, p63, and p73) is essential for their distinct functions in cell-cycle control and development. To elucidate the molecular basis for tetramer formation of the various family members, we solved the crystal structure of the human p73 tetramerization domain (residues 351-399). Similarly to the canonical p53 tetramer, p73 forms a tetramer with D(2) symmetry that can be described as a dimer of dimers. The most striking difference between the p53 and p73 tetramerization domain is the presence of an additional C-terminal helix in p73. This helix, which is conserved in p63, is essential for stabilizing the overall architecture of the tetramer, as evidenced by the different oligomeric structures observed for a shortened variant lacking this helix. The helices act as clamps, wrapping around the neighboring dimer and holding it in place. In addition, we show by mass spectrometry that the tetramerization domains of p63 and p73, but not p53, fully exchange, with different mixed tetramers present at equilibrium, albeit at a relatively slow rate. Taken together, these data provide intriguing insights into the divergent evolution of the oligomerization domain within the p53 family, from the ancestral p63/p73-like protein toward smaller, less promiscuous monomeric building blocks in human p53, allowing functional separation of the p53 pathway from that of its family members.

Original publication

DOI

10.1073/pnas.0905867106

Type

Journal article

Journal

Proc Natl Acad Sci U S A

Publication Date

20/10/2009

Volume

106

Pages

17705 - 17710

Keywords

Amino Acid Sequence, Animals, Crystallography, X-Ray, DNA-Binding Proteins, Evolution, Molecular, Genetic Variation, Humans, Models, Molecular, Molecular Sequence Data, Nuclear Proteins, Protein Structure, Quaternary, Recombinant Proteins, Sequence Homology, Amino Acid, Spectrometry, Mass, Electrospray Ionization, Thermodynamics, Trans-Activators, Transcription Factors, Tumor Protein p73, Tumor Suppressor Protein p53, Tumor Suppressor Proteins