Structural evolution of p53, p63, and p73: Implication for heterotetramer formation

Abstract

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.crystallography ͉ mass spectrometry ͉ tetramer ͉ transcription factor

Mechanism of TAp73 inhibition by ΔNp63 and structural basis of p63/p73 hetero-tetramerization

“…20 With respect to the three mammalian family members, along with others, we have shown that p53 does not form heterotetramers with either p63 or p73. 9,10 However, these investigations have also demonstrated that p63 and p73 form very stable hetero-tetramers. So far, all available data suggest that the question whether two different proteins can form heterotetramers or not is connected to the presence of a second helix in the TD.…”

“…8 In previous studies, along with others, we have shown that p63 and p73 can form mixed tetramers via their tetramerization domains (TDs). 9,10 Surprisingly, hetero-tetramers consisting of one homo p63 dimer and one homo p73 dimer are thermodynamically more stable than both homo-tetramers. This in vitro finding suggests that in cells that express both p73 as well as p63 mixed tetramers can exist.…”

Aggregation and Prion-Like Properties of Misfolded Tumor Suppressors: Is Cancer a Prion Disease?

“…Structurally, the DNA-binding domain is highly similar among these three proteins, maintaining the same b-sandwich fold . The oligomerization domains of p63 and p73 can form weak heterotetramers with each other, but not with the oligomerization domain of p53 because of their high sequence similarity, which is less similar to the sequence of p53 (Li and Prives 2007;Joerger et al 2009). …”

“…coaggregate with mutant p53. tetramers in p73 nor p63 homotetramers resulted in exchange after 24 h, indicating the divergent evolution of the oligomerization domain within the p53 family (Joerger et al 2009). Furthermore, a GoF phenotype associated with certain p53 mutants was shown based on their coaggregation with p63 and p73 (Xu et al 2011).…”

p73 – constitutively open for business

“…p63 and p73 (but not p53) can exchange dimers to form symmetrical p63:p73 heterotetramers with 2:2 stochiometry in vitro. 11 Helix H2 in the tetramerization domain of p63/p73 wraps around and is crucial to stabilize the active tetramer. This helix is missing in p53.…”