Cyclobutane pyrimidine dimers (CPDs) are the most abundant DNA lesions produced in mammalian cells upon exposure to UV-B radiation (280-315 nm) in sunlight. These photolesions are highly mutagenic and can lead to cancer. CPDs are thought to be chemically stable and to be able to withstand high concentrations of acids and bases. Indeed, while early investigations of the alkaline reactivity of sunlight-induced DNA lesions containing a saturated dihydouracil have shown that the ring C4 carbonyl group is a potential target of nucleophilic attack, similar reactions with model CPDs (formed from the dimerization of thymine nucleobases alone or thymidine nucleosides) clearly showed that the cis-syn CPD (major isomer formed upon UV-irradiation of mammalian cells) is stable in the presence of a high concentration of alkali at room temperature. Here we present results describing the reactivity of these lesions when contained within a true dinucleotide CPD model system. Our results using cis-syn CPD formed from dinucleotide 5'-TpT-3' combined with 18O labelling studies demonstrated that CPD undergoes a water addition at the C4=O groups of these now saturated rings leading to the formation of a hemiaminal intermediate. This intermediate, once formed, however, completely reverts to the starting lesion. Along with confirming the target of water addition within CPD lesions, we also determined that the two C4 carbonyls present on adjacent saturated pyrimidine rings of the photolesion (3' vs. 5') react asymmetrically and undergo water exchange at different rates. Moreover, this difference in reactivity is not limited to a dinucleotide and was observed in oligonucleotides (and various structural variants of CPD) as well. Overall, these results, and an understanding of the chemistry of CPD lesions in general, are crucial to our knowledge of DNA modifications and may lead to further insight into their chemical detection, modification, and biochemical recognition & repair.

Mechanistic studies of model cyclobutane pyrimidine dimer (CPD) DNA lesions under alkaline conditions

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.