%0 Journal Article
%A Szalai, Veronika A.
%A Singer, Melissa J.
%A Thorp, H. Holden
%D 2002
%T Site-Specific Probing of Oxidative Reactivity and Telomerase
Function Using 7,8-Dihydro-8-oxoguanine in Telomeric DNA
%U https://acs.figshare.com/articles/journal_contribution/Site-Specific_Probing_of_Oxidative_Reactivity_and_Telomerase_Function_Using_7_8-Dihydro-8-oxoguanine_in_Telomeric_DNA/3636108
%R 10.1021/ja0119651.s001
%2 https://acs.figshare.com/ndownloader/files/5724912
%K G quadruplex form
%K sequence
%K Telomeric DNA Telomeres
%K oxidation
%K G quadruplex formation
%K 8 OG
%K GTT
%K intramolecular G quadruplexes
%K GTTAGGGTGT
%K GGG triplet
%K telomerase activity
%K AG
%X Telomeres at the ends of human chromosomes contain the repeating sequence 5‘-d[(TTAGGG)n]-3‘. Oxidative damage of guanine in DNAs that contain telomeric and nontelomeric sequence generates
7,8-dihydro-8-oxoguanine (8OG) preferentially in the telomeric segment, because GGG sequences are
more reactive in duplex DNA. We have developed a general strategy for probing site-specific oxidation
reactivity in diverse biological structures through substitution of minimally modified building blocks that are
more reactive than the parent residue, but preserve the parent structure. In this study, 8OG was substituted
for guanine at G8, G9, G14, or G15 in the human telomeric oligonucleotide 5‘-d[AGGGTTAG8G9GTT AG14G15GTTAGGGTGT]-3‘. Replacement of G by 8OG in telomeric DNA can affect the formation of intramolecular
G quadruplexes, depending on the position of substitution. When 8OG was incorporated in the 5‘-position
of a GGG triplet, G quadruplex formation was observed; however, substitution of 8OG in the middle of a
GGG triplet produced multiple structures. A clear correspondence between structure and reactivity was
observed when oligonucleotides containing 8OG in the 5‘-position of a GGG triplet were prepared in the
quadruplex or duplex forms and interrogated by mediated electrocatalytic oxidation with Os(bpy)32+ (bpy =
2,2‘-bipyridine). The rate constant for one-electron oxidation of a single 8OG in the 5‘-position of a GGG
triplet was (6.2 ± 1.7) × 104 M-1 s-1 in the G quadruplex form. The rate constant was 2-fold lower for the
same telomeric sequence in the duplex form ((3.0 ± 1.3) × 104 M-1 s-1). The position of 8OG in the GGG
triplet affects telomerase activity and synthesis of telomeric repeat products. Telomerase activity was
decreased significantly when 8OG was substituted in the 5‘-position of the GGG triplet, but not when 8OG
was substituted in the middle of the triplet. Thus, biological oxidation of G to 8OG in telomeres has the
potential to modulate telomerase activity. Further, small molecules that inhibit telomerase by stabilizing
telomeric G quadruplexes may not be as effective under oxidative stress.
%I ACS Publications