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Strand- and site-specific DNA lesion demarcation by the xeroderma pigmentosum group D helicase

Nadine Mathieu1, Nina Kaczmarek, Hanspeter Naegeli

  • 1Institute of Pharmacology and Toxicology, University of Zürich-Vetsuisse, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.

Proceedings of the National Academy of Sciences of the United States of America
|September 30, 2010
PubMed

Insights

Xeroderma pigmentosum group D (XPD) protein anchors to UV-damaged DNA by selectively binding to cyclobutane pyrimidine dimers (CPDs) in one strand. This DNA repair mechanism ensures accurate excision of DNA damage.

Area of Science:

  • Molecular Biology
  • DNA Repair Mechanisms
  • Biochemistry

Background:

  • UV radiation exposure induces DNA damage, primarily cyclobutane pyrimidine dimers (CPDs), which trigger detrimental skin responses.
  • Placental mammals utilize nucleotide excision repair (NER) to eliminate CPDs, but the mechanism by which NER factors precisely locate and demarcate these lesions remains unclear.
  • The transcription factor TFIIH, containing the xeroderma pigmentosum group D (XPD) protein, is crucial for NER, involving DNA unwinding and lesion recognition.

Purpose of the Study:

  • To investigate the mechanism by which the XPD protein interacts with and recognizes CPDs in UV-exposed DNA.
  • To elucidate how XPD's ATPase/helicase activity contributes to the anchoring and demarcation of DNA lesions during the NER process.
  • To understand the strand selectivity of XPD binding to CPDs and its implications for DNA repair accuracy.

Main Methods:

  • Utilized a monomeric archaeal homolog of XPD to probe its interaction with CPDs in vitro.
  • Employed biochemical assays, including restriction and glycosylase protection assays, to analyze XPD binding to damaged DNA.
  • Conducted competition assays to determine the stability of XPD-DNA complexes based on CPD location and strand orientation.

Main Results:

  • XPD's collision with a CPD inhibits its helicase activity but stimulates its ATPase activity.
  • XPD helicase exhibits stable binding to CPDs located on the translocated strand (5'-3' polarity).
  • XPD dissociates from the DNA substrate when encountering a CPD on the complementary 3'-5' strand, indicating strand-selective recognition.

Conclusions:

  • XPD protein plays a critical role in verifying and demarcating DNA lesions through strand-selective immobilization.
  • The conversion of XPD's helicase activity to site-specific ATPase activity at CPDs ensures precise excision boundaries.
  • This mechanism highlights a crucial damage verification step in nucleotide excision repair, ensuring genomic integrity.

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