Crystal structure of human Mediator subunit MED23.

Area of Science:

• Molecular biology
• Structural biology
• Biochemistry

Background:

• The Mediator complex is crucial for eukaryotic transcription initiation, bridging enhancers and promoters.
• Human Mediator consists of 26 subunits organized into Head, Middle, and Tail modules.
• MED23 is the largest subunit of the Tail module and interacts with transcription activators.

Purpose of the Study:

• To determine the high-resolution crystal structure of the human MED23 subunit.
• To elucidate the structural organization of MED23 and its functional implications.
• To provide a structural basis for understanding Mediator's interaction with transcription factors.

Main Methods:

• X-ray crystallography at 2.8 Å resolution.
• Analysis of protein structure and domain organization.
• Biochemical characterization of MED23 interactions.

Main Results:

• The crystal structure of MED23 reveals 25 HEAT repeats-like motifs forming 5 α-solenoids.
• MED23 adopts an arch-shaped conformation with a protruding N-terminal domain.
• The structure displays triangular motifs and extended grooves, suggesting functional sites.

Conclusions:

• The MED23 structure provides atomic-level insights into the human Mediator Tail module.
• This structure rationalizes known biochemical data and explains MED23's role in transcription.
• It lays the groundwork for understanding Mediator's cross-talk with transcriptional activators.