Structural Basis of BRCC36 Function in DNA Repair and Immune Regulation

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Deubiquitinases (DUBs) are crucial for cellular processes but often considered constitutively active.
• The BRCA1-A and BRISC complexes, containing the BRCC36 DUB subunit, are involved in DNA double-strand break repair and immune signaling.
• The regulatory mechanisms and targeting specificities of these complexes were previously unknown.

Purpose of the Study:

• To elucidate the molecular basis of BRCA1-A and BRISC complex function.
• To understand how scaffold subunits ABRAXAS and ABRO1 modulate the activity of the BRCC36 deubiquitinase.
• To explain the diversified targeting and regulatory functions within the BRCC36 DUB family.

Main Methods:

• X-ray crystallography to determine the structures of the BRCA1-A and BRISC complexes.
• Biochemical assays to assess deubiquitinase activity and binding interactions.
• Analysis of protein-protein interactions between scaffold subunits and their targets.

Main Results:

• The BRCA1-A complex structure reveals ABRAXAS sequesters BRCA1 away from DNA break sites.
• The BRISC complex structure shows ABRO1 binding to SHMT2α, inhibiting BRCC36 activity.
• Different adaptor subunits confer specific targeting and regulatory functions to the BRCC36 DUB.

Conclusions:

• Scaffold subunits ABRAXAS and ABRO1 provide modularity and regulatory control to the BRCC36 deubiquitinase.
• This modularity allows for diverse roles in DNA repair, immune signaling, and metabolic regulation.
• The findings offer insights into the intricate regulation of deubiquitinase activity in mammals.