UC Davis

The guanine oxidation products, 5-guanidinohydantoin (Gh) and spiroiminodihydantoin (Sp), are mutagenic and toxic base lesions that are removed by Fpg, Nei, and the Nei-like (NEIL) glycosylases as the first step in base excision repair (BER). The hydantoins are excellent substrates for the NEIL glycosylases in a variety of DNA contexts beyond canonical duplex DNA, implicating the potential impact of repair activity on a multitude of cellular processes. In order to prepare stable derivatives as chemical biology tools, oligonucleotides containing fluorine at the 2'-position of the sugar of 8-oxo-7,8-dihydro-2'-deoxyguanosine2'-F-OG) were synthesized in ribo and arabino configuration. Selective oxidation of 2'-F-OG within a DNA oligonucleotide provided the corresponding 2'-F-Gh or 2'-F-Sp containing DNA. The 2'-F-hydantoins in duplex DNA were found to be highly resistant to the glycosylase activity of Fpg and NEIL1 compared to the unmodified lesion substrates. Surprisingly, however, some glycosylase-mediated base removal from both the 2'-F-ribo- and 2'-F-arabinohydantoin duplex DNA was observed. Notably, the associated β-lyase strand scission reaction of the 2'-F-arabinohydantoins was inhibited such that the glycosylases were "stalled" at the Schiff-base intermediate. Fpg and NEIL1 showed high affinity for the 2'-F-Gh duplexes in both ribo and arabino configurations. However, binding affinity assessed using catalytically inactive variants of Fpg and NEIL1 indicated higher affinity for the 2'-F-riboGh-containing duplexes. The distinct features of glycosylase processing of 2'-F-ribohydantoins and 2'-F-arabinohydantoins illustrate their utility to reveal structural insight into damage recognition and excision by NEIL and related glycosylases and provide opportunities for delineating the impact of lesion formation and repair in cells.