Stereoselectivity of human nucleotide excision repair promoted by defective hybridization.
To assess helical parameters that dictate fast or slow removal of carcinogen-DNA adducts, we probed human nucleotide excision repair (NER) activity with DNA containing L-deoxyriboses. Unlike natural lesions such as pyrimidine dimers or base adducts, L-deoxyribonucleosides (the mirror images of normal D-deoxyribonucleosides) involve neither the addition nor the loss of covalent bonds or functional groups and hence exclude modulation of repair efficiency by adduct chemistry and size. Previous studies showed that single L-deoxyribonucleosides distort DNA backbones but are accommodated in the double helix with intact hydrogen bonding between complementary strands. Here, we found that such single L-enantiomers are rejected as excision repair substrates in a NER-proficient cell extract. However, the same L-deoxyribose moiety stimulates NER activity upon incorporation into a nonhybridizing site of one or, more effectively, two base mismatches. In contrast to single L-deoxyriboses, multiple consecutive L-deoxyriboses interfere with normal hybridization; in this case, the intrinsic derangement of base pairing was sufficient to promote the excision of a cluster of three adjacent L-deoxyribonucleosides without any requirement for mismatches. Thus, using stereoselective substrates, we demonstrate the participation of a recognition subunit that guides human NER activity to sites of defective Watson-Crick strand pairing. This conformational sensor detects labile hydrogen bonds irrespective of the type of deoxyribonucleotide modification.
Institute of Pharmacology and Toxicology, University of Zürich-Tierspital, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.
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Hess
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Naegeli
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Capobianco
D020137:Base Pair Mismatch; D004249:DNA Damage / Q000235:genetics*; D004260:DNA Repair / Q000235:genetics*; D006801:Humans; D006860:Hydrogen Bonding; D009693:Nucleic Acid Hybridization; D013237:Stereoisomerism; D013379:Substrate Specificity