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Structure and dynamics of thioguanine-modified duplex DNA
Lilla Somerville1, Eugene Y Krynetski, Natalia F Krynetskaia
1Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
The Journal of Biological Chemistry
|October 29, 2002
Summary
Incorporating thioguanine into DNA subtly alters its structure but drastically reduces base pair stability, explaining its cytotoxic effects in leukemia treatment. This research clarifies the molecular mechanisms of antileukemic agents.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Mercaptopurine and thioguanine are key antileukemic drugs.
- Their therapeutic effect relies on incorporation into DNA as deoxy-6-thioguanosine.
- The precise molecular mechanism linking DNA incorporation to cytotoxicity remains unclear.
Purpose of the Study:
- To elucidate the molecular mechanisms by which thioguanine incorporation into DNA leads to cytotoxicity.
- To investigate the structural and dynamic effects of thioguanine modification on DNA.
Main Methods:
- Determined the solution structure of thioguanine-modified duplex DNA.
- Analyzed base pairing interactions, hydrogen bonding, and base pair opening.
- Measured DNA melting temperature and imino proton resonance.
- Assessed base pair lifetime and exchange rates.
Main Results:
- Thioguanine incorporation caused subtle, localized structural changes, with thioguanine in the keto form.
- Weakened Watson-Crick hydrogen bonds and a modest base pair opening were observed.
- Significantly decreased base pair lifetime (approx. 80-fold) and increased imino proton exchange rate.
- Reduced DNA melting temperature (approx. 6°C).
Conclusions:
- Thioguanine incorporation into DNA profoundly impacts DNA dynamics, not just structure.
- These dynamic changes provide mechanistic insight into cytotoxicity and enzyme interactions.
- Offers a molecular basis for protein recognition of thioguanine-substituted DNA sites.
- Explains the therapeutic efficacy of thiopurine antileukemic agents.