Structural details on mdm2-p53 interaction

Area of Science:

• Molecular Biology
• Protein Interactions
• Biochemistry

Background:

• Mdm2 is a key antagonist of p53, regulating its cellular levels through a negative feedback loop.
• p53 and Mdm2 physically interact, with initial studies identifying a helical region in p53 transactivation domain (TAD) mediating this binding.
• Previous work showed p53 TAD is largely unstructured but contains nascent turns and a preformed helix involved in Mdm2 binding.

Purpose of the Study:

• To investigate the binding capabilities of nascent turn motifs within p53 TAD to Mdm2.
• To elucidate the structural changes and binding affinities of these motifs upon interaction with Mdm2.
• To challenge the existing model of p53-Mdm2 interaction, suggesting a more complex binding mechanism.

Main Methods:

• Heteronuclear multidimensional Nuclear Magnetic Resonance (NMR) spectroscopy was employed.
• Analysis of protein-protein interactions between p53 TAD and Mdm2.
• Determination of binding affinities and structural characterization of interacting motifs.

Main Results:

• Two nascent turn motifs in p53 TAD, specifically turn I (residues 40-45) and turn II (residues 49-54), were found to bind Mdm2.
• The turn II motif exhibits a higher binding affinity (approximately 20 µM) compared to turn I and binds to the same site on Mdm2 as the helical motif.
• Upon Mdm2 binding, the turn II motif adopts a well-defined helical structure, with its hydrophobic face inserting into the Mdm2 binding pocket.

Conclusions:

• The interaction between p53 and Mdm2 is more intricate than previously understood, involving multiple, non-contiguous, and minimally structured motifs in p53 TAD.
• p53-Mdm2 binding involves global contacts rather than being localized to a single small helical domain.
• These findings suggest a dynamic and adaptable binding interface contributing to the regulation of p53 stability.