To protect cells from oxidative DNA damage and mutagenesis, organisms possess multiple glycosylases to recognize the damaged bases and to initiate the Base Excision Repair (BER) pathway. Recently, three DNA glycosylases were identified in mammals that are homologous to the Escherichia coli Fpg and Nei proteins, Neil1, Neil2 and Neil3. Neil1 and Neil2 in human and mouse have been well characterized while the properties of the Neil3 protein remain to be elucidated. In this study, we report the characterization of Mus musculus (house mouse) Neil3 (MmuNeil3) as an active DNA glycosylase both in vitro and in vivo. In duplex DNA, MmuNeil3 mainly recognizes oxidized purines, such as spiroiminodihydantoin (Sp), guanidinohydantoin (Gh), 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG) and 4,6-diamino- 5-formamidopyrimidine (FapyA), but not 8-oxo-7,8-dihydroguanine (8-oxoG). Interestingly, MmuNeil3 prefers lesions in single stranded DNA and in bubble structures. In contrast to other members of the family that use the N-terminal proline as the nucleophile, MmuNeil3 forms a Schiff Base intermediate via its N-terminal valine. In vivo, we expressed the glycosylase domain of MmuNeil3 (MmuNeil3 324) in an Escherichia coli triple mutant lacking Fpg, Nei and MutY glycosylase activities. Expression of MmuNeil3 324 greatly reduced the spontaneous mutation frequency of the triple mutant. Since the mutations observed in the triple mutant are all G to T transversions, this reduction in mutation frequency suggests that Neil3 plays a role in repairing guanine-derived lesions especially FapyG in vivo.
Citation: Proceedings of the National Academy of Sciences of the United States of America
Pub Type: Journals
Base Excision Repair, DNA glycosylases, NEIL3, Mus musculus, Guanidinohydantoin, Spiroiminodihydantoin , 2, 6-diamino- 4-hydroxy-5-formamidopyrimidine