The Formamidopyrimidines: Purine Lesions Formed in Competition With 8-Oxopurines From Oxidative Stress

Abstract

Conspectus DNA is constantly exposed to agents that induce structural damage, from sources both internal and external to an organism. Endogenous species, such as oxidizing chemicals, and exogenous agents, such as ultraviolet rays in sunlight, together produce more than 70 distinct chemical modifications of native nucleotides. Of these, about 15 of the lesions have been detected in cellular DNA. This kind of structural DNA damage can be cytotoxic, carcinogenic, or both, and is being linked to an increasingly lengthy list of diseases. The formamidopyrimidine (Fapy) lesions are a family of DNA lesions that result after purines undergo oxidative stress. The Fapy lesions are produced in yields comparable to the 8-oxopurines, which, owing in part to a perception of mutagenicity in some quarters, have been subjected to intense research scrutiny. But despite the comparable abundance of the formamidopyrimidines and the 8-oxopurines, until recently very little was known about the effects of Fapy lesions on biochemical processes involving DNA or on the structure and stability of the genomic material. In this Account, we discuss the detection of Fapy lesions in DNA and the mechanism proposed for their formation. We also describe methods for the chemical synthesis of oligonucleotides containing Fapy•dA or Fapy•dG and the outcomes of chemical and biochemical studies utilizing these compounds. These experiments reveal that the formamidopyrimidines decrease the fidelity of polymerases and are substrates for DNA repair enzymes. The mutation frequency of Fapy•dG in mammals is even greater than that of 8-oxodGuo (8-oxo-7,8-dihydro-2′-deoxyguanosine, one of the 8-oxopurines), suggesting that this lesion could be a useful biomarker and biologically significant. Despite clear similarities, the formamidopyrimidines have lived in the shadow of the corresponding 8-oxopurine lesions. But the recent development of methods for synthesizing oligonucleotides containing Fapy•dA or Fapy•dG has accelerated research on these lesions, revealing that the formamidopyrimidines are repaired as efficiently and, in some cases, more rapidly than the 8-oxopurines. Fapy•dG appears to be a lesion of biochemical consequence, and further study of its mutagenicity, repair, and interactions with DNA structure will better define the cellular details involving this important product of DNA stress.

Characterization of Nitrogen Mustard Formamidopyrimidine Adduct Formation of Bis(2-chloroethyl)ethylamine with Calf Thymus DNA and a Human Mammary Cancer Cell Line

“…34, 35, 70 N 5 -Substituted FapyG adducts have not been extensively studied, unlike the unsubstituted counterpart derived from oxidative damage. 71, 72 …”

Translesion Synthesis of 2′-Deoxyguanosine Lesions by Eukaryotic DNA Polymerases

“…4,5 The pathway leading to 8-oxo-dG is believed to involve a C8-hydroxyl radical, which also forms Fapy·dG (Figure 1). 6 …”

Looking beneath the surface to determine what makes DNA damage deleterious

“…The first concerns DNA replication and to a lesser extent transcription. The effects of numerous lesions on polymerase efficiency and fidelity have been determined in prokaryotic and eukaryotic cells [3–6]. In addition, the base excision and nucleotide excision repair pathways that remove a variety of lesions from damaged DNA, as well as the tailoring of the termini of cleaved DNA to prepare them as substrates for polymerase and/or ligase enzymes have been surveyed [7,8].…”