Repair of O6-methylguanine adducts in human telomeric G-quadruplex DNA by O6-alkylguanine-DNA alkyltransferase.
Bottom Line: Its functions with short single-stranded and duplex substrates have been characterized, but its ability to act on other DNA structures remains poorly understood.Here, we examine the functions of this enzyme on O(6)-methylguanine (6mG) adducts in the four-stranded structure of the human telomeric G-quadruplex.This distinction may reflect differences in the conformational dynamics of 6mG residues in G-quadruplex DNAs.
Affiliation: Department of Molecular and Cellular Biochemistry, Center for Structural Biology, University of Kentucky, Lexington, KY 40536, USA.Show MeSH
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Mentions: We used CD spectroscopy to test whether AGT binding alters the secondary structures of our quadruplex DNAs. Difference spectra (CDDNA+AGT – CDAGT) were obtained for the 22wt quadruplex in TE buffer containing 75 mM KCl and compared to spectra obtained at the same [DNA], but in the absence of AGT. As shown in Figure 6A, inclusion of AGT in the solution does not significantly change the DNA spectrum. This contrasts with the effect of AGT addition to a solution of the single-stranded 26-nt DNA, which results in a significant CD difference throughout the near-ultraviolet range (Figure 6B). These outcomes are simply explained by models in which AGT binding causes a substantial conformational shift in single-stranded 26-mer DNA, but not in the 22wt G-quadruplex.
Affiliation: Department of Molecular and Cellular Biochemistry, Center for Structural Biology, University of Kentucky, Lexington, KY 40536, USA.