Mechanism of Repair of Acrolein- and Malondialdehyde-Derived Exocyclic Guanine Adducts by the 伪-Ketoglutarate/Fe(II) Dioxygenase AlkB

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• 作者：Vipender Singh ; Bogdan I. Fedeles ; Deyu Li ; James C. Delaney ; Ivan D. Kozekov ; Albena Kozekova ; Lawrence J. Marnett ; Carmelo J. Rizzo ; John M. Essigmann
• 刊名：Chemical Research in Toxicology
• 出版年：2014
• 出版时间：September 15, 2014
• 年：2014
• 卷：27
• 期：9
• 页码：1619-1631
• 全文大小：565K
• ISSN：1520-5010

文摘

The structurally related exocyclic guanine adducts 伪-hydroxypropano-dG (伪-OH-PdG), 纬-hydroxypropano-dG (纬-OH-PdG), and M₁dG are formed when DNA is exposed to the reactive aldehydes acrolein and malondialdehyde (MDA). These lesions are believed to form the basis for the observed cytotoxicity and mutagenicity of acrolein and MDA. In an effort to understand the enzymatic pathways and chemical mechanisms that are involved in the repair of acrolein- and MDA-induced DNA damage, we investigated the ability of the DNA repair enzyme AlkB, an 伪-ketoglutarate/Fe(II) dependent dioxygenase, to process 伪-OH-PdG, 纬-OH-PdG, and M₁dG in both single- and double-stranded DNA contexts. By monitoring the repair reactions using quadrupole time-of-flight (Q-TOF) mass spectrometry, it was established that AlkB can oxidatively dealkylate 纬-OH-PdG most efficiently, followed by M₁dG and 伪-OH-PdG. The AlkB repair mechanism involved multiple intermediates and complex, overlapping repair pathways. For example, the three exocyclic guanine adducts were shown to be in equilibrium with open-ring aldehydic forms, which were trapped using (pentafluorobenzyl)hydroxylamine (PFBHA) or NaBH₄. AlkB repaired the trapped open-ring form of 纬-OH-PdG but not the trapped open-ring of 伪-OH-PdG. Taken together, this study provides a detailed mechanism by which three-carbon bridge exocyclic guanine adducts can be processed by AlkB and suggests an important role for the AlkB family of dioxygenases in protecting against the deleterious biological consequences of acrolein and MDA.