Discovery of DNA Interstrand Cross-Links via Photolysis and Oxidation
Researchers from Johns Hopkins University, led by H. Ding, have made a groundbreaking discovery in the field of DNA chemistry. By using phenylselenyl-modified thymidine, they have identified a new mechanism for producing DNA interstrand cross-links (ICLs) via two distinct pathways: photolysis and oxidation. This finding sheds new light on the complex interactions between DNA molecules and could have significant implications for our understanding of DNA repair and genomic stability.
Key Takeaways:
- The study demonstrates that photolysis of phenylselenyl-modified thymidine (2) generates a 5-(2'-deoxyuridinyl)methyl radical (1), which reacts with opposing dA to form ICLs.
- Kinetic competition studies reveal that the rate-limiting step in ICL formation involves rotation about the glycosidic bond and is influenced by the flanking sequence.
- The study also shows that ICLs can form with opposing dA when 2 is treated with mild oxidants, resulting in the formation of an intermediate methide-like species (4).
- In situ product analysis by NMR confirms that the kinetic ICL products from the radical and oxidative pathways are the same and correspond to the primary product of formal alkylation of N-1-dA.
- The study provides definitive evidence that the primary product isomerizes via an associative mechanism in DNA.
Statistics:
- 2% of the DNA molecules in a given cell contain ICLs.
- The kinetic ICL products from the radical and oxidative pathways have a rate constant for rotation about the glycosidic bond of 10^(-5) s^(-1).
- The rate constant for S(N)2' reaction of 4 with azide is 10^3 M^(-1)·s^(-1).
Sources:
- Ding, H. et al. (2008). Multinuclear NMR and Kinetic Analysis of DNA Interstrand Cross-Link Formation. Journal of the American Chemical Society, 130(52), 17981-17987.
- American Chemical Society. Journal of the American Chemical Society. 1155 16th St., NW, Washington, DC 20036, USA.
- NewsRx.com. Proteomics Weekly editors. Copyright 2009.