Stability of p53 oligomers: Tetramerization of p53 impinges on its stability.

The p53 protein has been known to exist structurally in three different forms inside the cells. Earlier studies have reported the predominance of the lower oligomeric forms of p53 over its tetrameric form inside the cells, although only the tetrameric p53 contributes to its transcriptional activity. However, it remains unclear the functional relevance of the existence of other p53 oligomers inside the cells. In this study, we characterize the stability and conformational state of tetrameric, dimeric and monomeric p53 that spans both DNA Binding Domain (DBD) and Tetramerization Domain (TD) of human p53 (94-360 amino acid residues). Intriguingly, our studies reveal an unexpected drastic reduction in tetrameric p53 thermal stability in comparison to its dimeric and monomeric form with a higher propensity to aggregate at physiological temperature. Our EMSA study suggests that tetrameric p53, not their lower oligomeric counterpart, exhibit rapid loss of binding to their consensus DNA elements at the physiological temperature. This detrimental effect of destabilization is imparted due to the tetramerization of p53 that drives the DBDs to misfold at a faster pace when compared to its lower oligomeric form. This crosstalk between DBDs is achieved when it exists as a tetramer but not as dimer or monomer. Our findings throw light on the plausible reason for the predominant existence of p53 in dimer and monomer forms inside the cells with a lesser population of tetramer form. Therefore, the transient disruption of tetramerization between TDs could be a potential cue for the stabilization of p53 inside the cells.

Phosphomimetic Mutation Destabilizes the Central Core Domain of Human p53.

Transcriptional activity of p53 is modulated by various posttranslational modifications. Earlier studies have reported that Aurora B phosphorylation of p53 leads to loss of its transcriptional activity, subsequently leading to its ubiquitin-mediated proteasomal degradation. To decipher the fate of structural and functional stature of p53 upon phosphorylation by Aurora B, we have generated five phosphomimetic mutants of p53 core domain and characterized their biophysicochemical properties. Our biophysical studies show that the T211E, S215E, and S269E mutants are thermally unstable and show a higher propensity toward aggregation than WT with the loss of DNA binding except for S183E. These results indicate structural and functional destabilization of p53 upon phosphomimetic substitution, which provides a molecular basis toward understanding the process that drives the fate of p53 upon phosphorylation by Aurora B kinase. © 2018 IUBMB Life, 70(10):1023-1031, 2018.