Human XPG nuclease structure, assembly, and activities with insights for neurodegeneration and cancer from pathogenic...

Area of Science:

• Molecular Biology
• Genetics
• Structural Biology

Background:

• Xeroderma pigmentosum group G (XPG) protein is crucial for DNA repair, specifically nucleotide excision repair (NER).
• Mutations in the XPG gene (ERCC5) cause distinct diseases: cancer-prone xeroderma pigmentosum (XP-G) and neurodevelopmental Cockayne syndrome (XP-G/CS).
• The structural basis for XPG's diverse roles in DNA damage responses (DDR) and disease phenotypes remains unclear.

Purpose of the Study:

• To elucidate the structural mechanism underlying XPG's distinct disease phenotypes (XP-G vs. XP-G/CS).
• To understand the structural basis for XPG's function in multiple DNA damage responses (DDR).
• To reveal XPG-specific features for its activities and regulation.

Main Methods:

• Crystal structure determination of the human XPG catalytic domain (XPGcat).
• Biochemical assays, small-angle X-ray scattering (SAXS), and electron microscopy (EM).
• Analysis of pathogenic point mutations in relation to XPG structure and function.

Main Results:

• The crystal structure of XPGcat reveals unique features for DNA binding and regulation.
• Pathogenic mutations in XPGcat destabilize the protein, reduce cellular levels, and correlate with specific disease phenotypes.
• XPG forms a homodimer that binds, unstacks, and bends duplex DNA at internal unpaired regions, suggesting roles in NER and replication fork processing.
• XPG acts as a scaffold and DNA sculptor in multiple DDR pathways.

Conclusions:

• Structural insights into XPGcat explain disease divergence based on mutation location and impact on protein stability and function.
• XPG's DNA sculpting ability is key to its scaffolding role in maintaining genome stability across various DDR pathways.
• Understanding XPG structure-function relationships is critical for deciphering its role in DNA repair and associated human diseases.