cl03119

N-terminal domain of Fpg (formamidopyrimidine-DNA glycosylase, MutM)_Nei (endonuclease VIII) base-excision repair DNA glycosylases; DNA glycosylases maintain genome integrity by recognizing base lesions created by ionizing radiation, alkylating or oxidizing agents, and endogenous reactive oxygen species. These enzymes initiate the base-excision repair process, which is completed with the help of enzymes such as phosphodiesterases, AP endonucleases, DNA polymerases and DNA ligases. DNA glycolsylases cleave the N-glycosyl bond between the sugar and the damaged base, creating an AP (apurinic/apyrimidinic) site. The FpgNei DNA glycosylases represent one of the two structural superfamilies of DNA glycosylases that recognize oxidized bases (the other is the HTH-GPD superfamily exemplified by Escherichia coli Nth). Most FpgNei DNA glycosylases use their N-terminal proline residue as the key catalytic nucleophile, and the reaction proceeds via a Schiff base intermediate. One exception is mouse Nei-like glycosylase 3 (Neil3) which forms a Schiff base intermediate via its N-terminal valine. In addition to this FpgNei_N domain, FpgNei proteins have a helix-two-turn-helix (H2TH) domain and a zinc (or zincless)-finger motif which also contribute residues to the active site. FpgNei DNA glycosylases have a broad substrate specificity. They are bifunctional, in addition to the glycosylase (recognition) activity, they have a lyase (cleaving) activity on the phosphodiester backbone of the DNA at the AP site. This superfamily includes eukaryotic, bacterial, and viral proteins.