1n17

Structure and Dynamics of Thioguanine-modified Duplex DNA

spinqualitylabelsall models 1n17, 20 NMR models Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 1n17 is a 2 chain structure. Full experimental information is available from OCA. For a guided tour on the structure components use FirstGlance. NonStd Res: S6G Related: 1n14 Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Publication Abstract from PubMed Mercaptopurine and thioguanine, two of the most widely used antileukemic agents, exert their cytotoxic, therapeutic effects by being incorporated into DNA as deoxy-6-thioguanosine. However, the molecular mechanism(s) by which incorporation of these thiopurines into DNA translates into cytotoxicity is unknown. The solution structure of thioguanine-modified duplex DNA presented here shows that the effects of the modification on DNA structure were subtle and localized to the modified base pair. Specifically, thioguanine existed in the keto form, formed weakened Watson-Crick hydrogen bonds with cytosine and caused a modest approximately 10 degrees opening of the modified base pair toward the major groove. In contrast, thioguanine significantly altered base pair dynamics, causing an approximately 80-fold decrease in the base pair lifetime with cytosine compared with normal guanine. This perturbation was consistent with the approximately 6 degrees C decrease in DNA melting temperature of the modified oligonucleotide, the 1.13 ppm upfield shift of the thioguanine imino proton resonance, and the large increase in the exchange rate of the thioguanine imino proton with water. Our studies provide new mechanistic insight into the effects of thioguanine incorporation into DNA at the level of DNA structure and dynamics, provide explanations for the effects of thioguanine incorporation on the activity of DNA-processing enzymes, and provide a molecular basis for the specific recognition of thioguanine-substituted sites by proteins. These combined effects likely cooperate to produce the cellular responses that underlie the therapeutic effects of thiopurines. Structure and dynamics of thioguanine-modified duplex DNA.,Somerville L, Krynetski EY, Krynetskaia NF, Beger RD, Zhang W, Marhefka CA, Evans WE, Kriwacki RW J Biol Chem. 2003 Jan 10;278(2):1005-11. Epub 2002 Oct 24. PMID:12401802 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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