DNA−Protein Cross-links between Guanine and Lysine Depend on the Mechanism of Oxidation for Formation of C5 Vs C8 Guanosine Adducts

Abstract

The reaction between N(alpha)-acetyllysine methyl ester (Lys) and 2'-deoxyguanosine (dGuo) was used to study structural aspects of DNA-protein cross-link (DPC) formation. The precise structure of DPCs depended on the nature of the oxidant and cross-linking reactions in which a series of different oxidation conditions generated a distribution of adducts, principally spirodiiminodihydantoins with lysine appended at the purine position of C5 (5-Lys-Sp), C8 (8-Lys-Sp), or both C5 and C8 (5,8-diLys-Sp). Singlet oxygen oxidation of dGuo produced 5-Lys-Sp exclusively when Rose Bengal or methylene blue was used to photochemically generate (1)O2 in the presence of Lys, whereas riboflavin or benzophenone-mediated photochemistry generated lysine radicals and led to C8 adduct formation, yielding 8-Lys-Sp and 5,8-diLys-Sp. Notably, the yield of dGuo modifications from riboflavin photooxidation increased dramatically in the presence of lysine. Oxidation of deoxyguanosine/lysine mixtures with Na2IrCl6 or sulfate radicals produced both 5-Lys-Sp and 8-Lys-Sp. The same adducts were formed in single and double-stranded oligodeoxynucleotides, and these could be analyzed after nuclease digestion. Adduct formation in duplex DNA was somewhat dependent on the accessibility of lysine to C5 vs C8 of the purine. No adduct formation was detected between lysine and the other nucleobases T, C, or A. Overall, the precise location of adduct formation at C5 vs C8 of guanine appears to be diagnostic of the oxidation pathway.

Characterization of 2′-deoxyguanosine oxidation products observed in the Fenton-like system Cu(ii)/H2O2/reductant in nucleoside and oligodeoxynucleotide contexts

“…Reactions were also conducted using cysteine as the reductant, and in order to avoid amine adducts to electrophilic dG oxidation intermediates, N-acetyl-cysteine (NAC) was used. 53,54 …”

Nano-sized SnO₂ Photocatalysts: Synthesis, Characterization and Their Application for the Degradation of Methylene Blue Dye

“…Although there has been considerable success in the synthesis of SnO 2 nanomaterials of various morphologies [17][18][19][20], it is still a major challenge to prepare SnO 2 nanocrystals (NCs) with dimensions of less than 10 nm in different discrete sizes and relatively high BET surface area which is essential features for higher photocatalytic activity [21,22]. Furthermore, to date, many SnO 2 -based coupled semiconductor composite photocatalysts, such as SnO 2 -TiO 2 [23][24][25][26], SnO 2 -ZnO [27][28][29][30][31] or SnO 2 -CuO [32] have been extensively studied for their high photocatalytic activities.…”

Copper generated reactive oxygen leads to formation of lysine–DNA adducts

“…These adducts are likely DNA-protein crosslinks though it is currently experimentally challenging to identify these types of modifications in cells. Burrows et al showed that a crosslink between guanine base and lysine can occur when oxidized by photo-oxidants like rose bengal or riboflavin and by stoichiometric one-electron oxidants like Ir(IV) [10]. If these lesions occur in cells then their formation should be catalyzed by reactive oxygen species generated from copper or iron.…”

“…The Gh lesion is thought to form directly from the intermediate by loss of CO 2 at position six [26]. Protein-based nucleophiles have been observed to be covalently bound to DNA under oxidative conditions [10]. As a model of this complex reaction we will characterize guanine-lysine adduct formation in a nucleoside, an oligonucleotide, and a large DNA.…”