Title
Allosteric interactions by p53 mRNA governs HDM2 E3 ubiquitin ligase specificity under different conditions
Author
Ixaura Medina-Medina, Paola García-Beltran, Ignacio de la Mora-de la Mora, Jesús Oria-Hernández, Guy Millot, Robin Fahraeus, Horacio Reyes-Vivas, José G. Sampedro, Vanesa Olivares-Illana
Year
2016
Journal
Molecular and Cellular Biology
Abstract
HDM2 and HDMX are key negative regulatory factors of the p53 tumour suppressor under normal conditions by promoting its degradation or preventing its trans-activity, respectively. It has more recently been shown that both proteins can also act as positive regulators of p53 after DNA damage. This involves phosphorylation by ATM on serine residues HDM2(S395) and HDMX(S403), promoting their respective interaction with the p53 mRNA. But the underlying molecular mechanisms of how these phosphorylation events switch HDM2 and HDMX from negative to positive regulator of p53 is not known. Our results show that these phosphorylation events reside within intrinsically disordered domains and change the conformation of the proteins. The modifications promote the exposition of N-terminal interfaces that support the formation of a new HDMX:HDM2 heterodimer independent of the C-terminal RING-RING interaction. The E3 ubiquitin ligase activity of this complex towards p53 is prevented by thep53 mRNA ligand but, interestingly, does not affect the capacity to ubiquitinate HDMX and HDM2. These results show how ATM-mediated modifications of HDMX and HDM2 switch HDM2 E3 ubiquitin ligase activity away from p53 but towards HDMX and itself and illustrate how the substrate specificity of HDM2 E3 ligase activity is regulated.
Instrument
J-810
Keywords
Circular dichroism, Secondary structure, Tertiary structure, Biochemistry