Structure of a 13-fold superhelix (almost) determined from first principles

Area of Science:

• Structural biology
• Molecular biology
• Biochemistry

Background:

• Nuclear hormone receptors are key transcription factors.
• Co-activators like TIF2 are essential for their function.
• Structural studies often use peptide mimics of co-activators.

Purpose of the Study:

• To co-crystallize the glucocorticoid receptor with a ligand and TIF2 peptide.
• To determine the structure of the TIF2 co-activator peptide complex.
• To explore fragment-based molecular replacement for phasing.

Main Methods:

• Co-crystallization of glucocorticoid receptor, ligand, and TIF2 peptide.
• X-ray crystallography and diffraction data collection (1.82 Å resolution).
• Fragment-based molecular replacement using ARCIMBOLDO, PHASER, and SHELXE.

Main Results:

• HPLC confirmed only TIF2 peptide was present in crystals.
• Unanticipated superhelical structure with left-handed twist was observed.
• Ligand interactions stabilized the observed superhelical structure.

Conclusions:

• Fragment-based molecular replacement can accelerate phasing for native diffraction data.
• The study reveals novel structural insights into TIF2 peptide behavior.
• Confirms the utility of fragment-based approaches in structural biology.