XPD Helicase Structures and Activities: Insights into the Cancer and Aging Phenotypes from XPD Mutations

Abstract

Mutations in XPD helicase, required for nucleotide excision repair (NER) as part of the transcription/repair complex TFIIH, cause three distinct phenotypes: cancer-prone xeroderma pigmentosum (XP), or aging disorders Cockayne syndrome (CS), and trichothiodystrophy (TTD). To clarify molecular differences underlying these diseases, we determined crystal structures of the XPD catalytic core from Sulfolobus acidocaldarius and measured mutant enzyme activities. Substrate-binding grooves separate adjacent Rad51/RecA-like helicase domains (HD1, HD2) and an arch formed by 4FeS and Arch domains. XP mutations map along the HD1 ATP-binding edge and HD2 DNA-binding channel and impair helicase activity essential for NER. XP/CS mutations both impair helicase activity and likely affect HD2 functional movement. TTD mutants lose or retain helicase activity but map to sites in all four domains expected to cause framework defects impacting TFIIH integrity. These results provide a foundation for understanding disease consequences of mutations in XPD and related 4Fe-4S helicases including FancJ.

Effect of mutations in XPD(ERCC2) on pregnancy and prenatal development in mothers of patients with trichothiodystrophy or xeroderma pigmentosum

“…15,21 Our XP and TTD patients had XPD mutations that are similar to those previously published. 1,5,[8][9][10][11] All of our XP and TTD patients were compound heterozygotes for two different XPD mutations. Many XP patients had the common p.R683W mutation combined with other mutations.…”

“…There are several reasons why we believe that the prediction by Moslehi et al 19 that mutations in the C-terminal region of XPD [8][9][10] cause pre-eclampsia may not be correct. There is a complex genotype-phenotype relationship between the location of mutations in the human XPD gene and the presence or absence of clinical features of XP or TTD.…”

“…There is a complex genotype-phenotype relationship between the location of mutations in the human XPD gene and the presence or absence of clinical features of XP or TTD. Mutations are spread out along the 761 amino-acid structure of XPD in both disorders 1,5,[8][9][10][11] The mutations may affect nucleotide-excision repair and/or transcription to different extents. 2,3 In addition, some mutations are found in both XP and TTD patients.…”

Analysis of iron–sulfur protein maturation in eukaryotes

“…The DNA helicase Rad3 (XPD in humans) is one of the ten subunits of the RNA polymerase transcription factor IIH and is vital for nucleotide excision DNA repair 33 . A prokaryotic homolog of Rad3 has been shown by biochemical and structural studies to contain an essential [4Fe-4S] cluster inserted into its helicase fold 31,34 . This protocol describes various experimental approaches to verify that these proteins in fact contain Fe/S clusters in the living cell.…”

Phenotype-specific adverse effects of XPD mutations on human prenatal development implicate impairment of TFIIH-mediated functions in placenta

“…R112H maps to a residue in contact with the 4Fe-4S cluster and disrupts the helicase activity of XPD. 42 Three of the four TTD cases in our study, which were not associated with preeclampsia were R112H homozygotes. These observations suggested that gestational complications in the R112H:T482D heterozygote TTD case were driven by the T482D allele.…”