Repair of O6-methylguanine adducts in human telomeric G-quadruplex DNA by O6-alkylguanine-DNA alkyltransferase

Lance M. Hellman, Tyler J. Spear, Colton J. Koontz, Manana Melikishvili, Michael G. Fried

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


O6-alkylguanine-DNA alkyltransferase (AGT) is a single-cycle DNA repair enzyme that removes promutagenic O6-alkylguanine adducts from DNA. 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 O6methylguanine (6mG) adducts in the four-stranded structure of the human telomeric G-quadruplex. On a folded 22-nt G-quadruplex substrate, binding saturated at 2 AGT: DNA, significantly less than the ∼5 AGT: DNA found with linear single-stranded DNAs of similar length, and less than the value found with the telomere sequence under conditions that inhibit quadruplex formation (4 AGT:DNA). Despite these differences, AGT repaired 6mG adducts located within folded G-quadruplexes, at rates that were comparable to those found for a duplex DNA substrate under analogous conditions. Repair was kinetically biphasic with the amplitudes of rapid and slow phases dependent on the position of the adduct within the G-quadruplex: in general, adducts located in the top or bottom tetrads of a quadruplex stack exhibited more rapid-phase repair than did adducts located in the inner tetrad. This distinction may reflect differences in the conformational dynamics of 6mG residues in G-quadruplex DNAs.

Original languageEnglish
Pages (from-to)9781-9791
Number of pages11
JournalNucleic Acids Research
Issue number15
StatePublished - Sep 2 2014

Bibliographical note

Funding Information:
National Institutes of Health (NIH) [GM-070662 to M.G.F.]. Funding for open access charge: NIH [GM-070662 to M.G.F.]. Conflict of interest statement. None declared.

Publisher Copyright:
© The Author(s) 2014.

ASJC Scopus subject areas

  • Genetics


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