A role for intersubunit interactions in maintaining SAGA deubiquitinating module structure and activity

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The deubiquitinating module (DUBm) of the SAGA coactivator is essential for gene regulation.
• Ubp8, a deubiquitinating enzyme, requires interaction with other subunits like Sgf11 for its catalytic activity.

Purpose of the Study:

• To investigate the structural and functional role of the Sgf11 zinc finger (Sgf11-ZnF) in Ubp8 activity.
• To elucidate the mechanism by which Sgf11 stabilizes the active conformation of Ubp8 within the DUBm.

Main Methods:

• Structural studies (e.g., X-ray crystallography, NMR)
• Solution-based biophysical techniques
• Site-directed mutagenesis to analyze Ubp8 and Sgf11 variants

Main Results:

• Deletion of Sgf11-ZnF destabilizes Ubp8 incorporation into the DUBm, leading to domain swapping.
• Loss of Sgf11-ZnF misaligns active site residues of Ubp8, reducing its catalytic efficiency.
• Activating mutations in Ubp8 promote a monomeric DUBm form in the absence of Sgf11-ZnF.

Conclusions:

• Sgf11 plays a critical role in maintaining the active conformation of Ubp8 within the DUBm.
• Sgf11 compensates for the lack of intrinsic structural features that stabilize Ubp8's active site.
• Understanding Sgf11's function provides insights into the regulation of deubiquitinating enzymes.