Structural Basis for the Interaction between p53 Transactivation Domain and the Mediator Subunit MED25

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• Eukaryotic transcription initiation relies on interactions between transcriptional activators and the mediator complex.
• The p53 transcription factor's interaction with MED25 is crucial for its gene transcription activity.

Purpose of the Study:

• To characterize the molecular interaction between the p53 transactivation domain (p53TAD) and the activator interaction domain (ACID) of MED25.
• To elucidate the structural basis of this interaction and its conservation across different transcriptional activators.

Main Methods:

• Nuclear magnetic resonance (NMR) spectroscopy for chemical shift perturbation studies.
• Isothermal titration calorimetry (ITC) to quantify binding thermodynamics.
• Mutagenesis studies to identify key interaction regions.

Main Results:

• NMR and ITC data indicated that p53TAD interacts with MED25 ACID primarily via the p53TAD2 sequence motif.
• A refined structural model revealed that an α-helix from p53TAD2 binds to a hydrophobic groove on MED25 ACID.
• The study identified a conserved interaction mechanism between MED25 and acidic transactivation domains (TADs) from various activators, including p53, ERM, and VP16.

Conclusions:

• The p53TAD2 motif is essential for binding to MED25 ACID.
• The interaction is structurally defined by an α-helix engaging a hydrophobic groove.
• MED25 employs a conserved mechanism to interact with diverse intrinsically unfolded acidic TADs, highlighting its role in transcriptional regulation.