Figure 1: The hydrogen-bonded guanine tetrad. R represents 2'-deoxyribose residue.

Mentions: DNA and RNA containing runs of consecutive guanine bases may adopt four-stranded conformations based on the hydrogen-bonded guanine tetrad, or G-quartet (Fig. 1) [1–3]. The hydrogen-bonded guanine tetrad, or G-quartet are stabilized by monovalent ions such as sodium and potassium [4–7]. Such tetraplexes have been implicated in a variety of biological roles, including the function of chromosome telomeres [8], the dimerization of the human immunodeficiency virus RNA genome [9], the site-specific recombination of immunoglobulin genes [10], L1 retropositions [11], promoter regions of DNA such as the triplet repeat sequence that causes fragile-X syndrome [12–14], the retinoblastoma susceptibility gene [15], the chicken β-globulin gene [16], and the insulin gene-linked polymorphic region (ILPR) [17–20]. Their functional importance is supported by the isolation of proteins that bind and promote the formation of tetraplex structure [21, 22].

Iwahashi H - J Clin Biochem Nutr (2008)

Bottom Line: Here effect of the hydroxylation of guanosine at the 8 position on the G-quartet formation was examined.On the other hand, the ESI-MS spectra of 8-oxodG in the presence of 0.1 mM NaCl shows prominent peaks at m/z 306 and m/z 589, corresponding to [8-oxodG + Na](+) and [8-oxodG(2) + Na](+).The results showed that 8-oxodG forms a relatively unstable tetrameric structure compared with dG.

Affiliation: Department of Chemistry, Wakayama Medical University, 811-1 Kimiidera, Wakayama 641-8509, Japan.

Abstract: The hydrogen-bonded guanine tetrad, or G-quartet has been implicated in a variety of biological roles, including the function of chromosome telomeres. Here effect of the hydroxylation of guanosine at the 8 position on the G-quartet formation was examined. Electrospray inonization mass (ESI-MS) spectra of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 2'-deoxyguanosine (dG) were measured in order to know whether or not 8-oxodG forms a tetrameric structure as 2'-deoxyguanosine forms in teromeres. The ESI-MS spectra of dG shows prominent peaks at m/z 290, m/z 557, and m/z 1092, corresponding to [dG + Na](+), [dG2 + Na](+), and [dG(4) + Na](+) in the presence of 0.1 mM NaCl. On the other hand, the ESI-MS spectra of 8-oxodG in the presence of 0.1 mM NaCl shows prominent peaks at m/z 306 and m/z 589, corresponding to [8-oxodG + Na](+) and [8-oxodG(2) + Na](+). The results showed that 8-oxodG forms a relatively unstable tetrameric structure compared with dG.