In vivo destabilization and functional defects of the xeroderma pigmentosum C protein caused by a pathogenic missense...

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Xeroderma pigmentosum group C (XPC) protein is vital for recognizing DNA damage in global genome nucleotide excision repair (NER).
• A specific mutation (Trp690Ser) in XPC was identified in patient XP13PV, leading to NER deficiency.

Purpose of the Study:

• To investigate the functional consequences of the Trp690Ser substitution in the XPC protein.
• To elucidate the molecular mechanisms underlying NER inactivation in XP13PV.

Main Methods:

• Analysis of XPC protein stability and steady-state levels in XP13PV fibroblasts.
• Assessment of heterotrimeric complex formation and interactions with NER factors.
• Evaluation of DNA binding affinity of the mutant XPC protein.
• Investigation of XPC localization to UV-damaged DNA sites and colocalization with other NER factors (UV-DDB, TFIIH, XPA).

Main Results:

• The Trp690Ser substitution significantly reduces XPC protein stability and its steady-state level.
• Mutant XPC forms normal complexes but lacks DNA binding affinity.
• XPC mutant accumulates at UV-damaged sites via UV-DDB, but fails to stably recruit TFIIH and XPA.
• The mutation causes both quantitative (stability) and qualitative (DNA binding) defects in XPC function.

Conclusions:

• The Trp690Ser substitution in XPC is sufficient to abolish NER function through reduced protein stability and impaired DNA binding.
• UV-DDB is important for recruiting XPC to damaged DNA sites.
• XPC's DNA binding is critical for the assembly of downstream NER intermediate complexes.