Oxidation of single-stranded oligonucleotides by carbonate radical anions: generating intrastrand cross-links between guanine and thymine bases separated by cytosines.
The carbonate radical anion is a biologically important one-electron oxidant that can directly abstract an electron from guanine, the most easily oxidizable DNA base. Oxidation of the 5'-d(CCTACGCTACC) sequence by photochemically generated CO3*- radicals in low steady-state concentrations relevant to biological processes results in the formation of spiroiminodihydantoin diastereomers and a previously unknown lesion. The latter was excised from the oxidized oligonucleotides by enzymatic digestion with nuclease P1 and alkaline phosphatase and identified by LC-MS/MS as an unusual intrastrand cross-link between guanine and thymine. In order to further characterize the structure of this lesion, 5'-d(GpCpT) was exposed to CO3*- radicals, and the cyclic nature of the 5'-d(G*pCpT*) cross-link in which the guanine C8-atom is bound to the thymine N3-atom was confirmed by LC-MS/MS, 1D and 2D NMR studies. The effect of bridging C bases on the cross-link formation was studied in the series of 5'-d(GpC(n)pT) and 5'-d(TpC(n)pG) sequences with n = 0, 1, 2 and 3. Formation of the G*-T* cross-links is most efficient in the case of 5'-d(GpCpT). Cross-link formation (n = 0) was also observed in double-stranded DNA molecules derived from the self-complementary 5'-d(TTACGTACGTAA) sequence following exposure to CO3*- radicals and enzymatic excision of the 5'-d(G*pT*) product.
Crean
Conor
C
Chemistry Department and Radiation and Solid State Laboratory, 31 Washington Place, New York University, New York, NY 10003-5180, USA.
Uvaydov
Yuriy
Y
Geacintov
Nicholas E
NE
Shafirovich
Vladimir
V
D000838:Anions; D002254:Carbonates / Q000737:chemistry*; D002853:Chromatography, Liquid; D003432:Cross-Linking Reagents / Q000737:chemistry; D003596:Cytosine / Q000737:chemistry*; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004583:Electrons; D005609:Free Radicals / Q000737:chemistry; D006147:Guanine / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D009841:Oligonucleotides / Q000737:chemistry*; D010084:Oxidation-Reduction; D053719:Tandem Mass Spectrometry; D013941:Thymine / Q000737:chemistry*
D000838:Anions; D002254:Carbonates; D003432:Cross-Linking Reagents; D005609:Free Radicals; D009841:Oligonucleotides; D006147:Guanine; D003596:Cytosine; D004247:DNA; D013941:Thymine