Competitive binding between dynamic p53 transactivation subdomains to human MDM2 protein: implications for regulating the p53·MDM2/MDMX interaction.

The interaction between the transactivation domain of p53 (p53TAD) and the N-terminal domain of MDM2 and MDMX plays an essential role for cell function. Mutations in these proteins have been implicated in many forms of cancer. The intrinsically disordered p53TAD contains two subdomains, TAD1 and TAD2. Using NMR spectroscopy, site-directed mutagenesis, and molecular dynamics simulations, we demonstrate that TAD2 directly interacts with MDM2, adopting transient structures that bind to the same hydrophobic pocket of MDM2 as TAD1. Our data show that binding of TAD1 and TAD2 to MDM2 is competitive, which is further supported by the observation that the interaction of TAD2 with MDM2 can be blocked by the small molecule inhibitor nutlin-3. Our data further indicate that TAD2 interacts with MDMX in a fashion very similar to MDM2. Because TAD2 is known to have transcriptional activity, the interaction of TAD2 with MDM2/MDMX may play a direct role in the inhibition of p53 transactivation.