Abstract
Formamidopyrimidines (Fapy) lesions result from ring opening of the imidazole portion of purines. Fapy lesions can isomerize from the natural β-anomeric stereochemistry to the α-configuration. We have unambiguously demonstrated that the α-methyl-Fapy-dG (MeFapy-dG) lesion is a substrate for Escherichia coli Endonuclease IV (Endo IV). Treatment of a MeFapy-dG-containing 24 mer duplex with Endo IV resulted in 36–40% incision. The catalytic efficiency of the incision was comparable to that of α-dG in the same duplex sequence. The α- and β-MeFapy-dG anomers equilibrate to ~21 : 79 ratio over ~3 days. Related studies with a duplex containing the α-Fapy-dG lesion derived from aflatoxin B1 epoxide (α-AFB-Fapy-dG) showed only low levels of incision. It is hypothesized that the steric bulk of the aflatoxin moiety interferes with the binding of the substrate to Endo IV and the incision chemistry.
Highlights
Formamidopyrimidines (Fapy) are DNA lesions that result from ring opening of the imidazole portion of purines
We recently described the synthesis of a phosphoramidite reagent of the MeFapy-dG lesion and its utility in the sitespecific synthesis of modified oligonucleotides [11]
The MeFapy-dG lesion was site incorporated at position 12 of the 24 mer oligonucleotide shown in Figure 2 (X = MeFapy-dG) and annealed to its complementary strand
Summary
Formamidopyrimidines (Fapy) are DNA lesions that result from ring opening of the imidazole portion of purines. Fapy lesions derived from dG can form by either initial oxidation or N7-alkylation of the guanine base (Scheme 1) [1,2,3,4,5,6]. These are structurally related lesions that differ by the substitution at the N5-formamide. The formyl nitrogen of the Fapy-dG derived from oxidative damage is unsubstituted, and it has been proposed that recognition of this lesion by human OGG involves hydrogen-bonding interactions between the protein and this functional group [7]. The corresponding Fapy-dG adducts were shown to be the persistent DNA lesions resulting from exposure to methylating agents (MeFapy-dG) and aflatoxin B1 (AFB-Fapy-dG) [8,9,10]
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