title: Biochemical mapping of human NEIL1 DNA glycosylase and AP lyase activities.
abstract: Base excision repair of oxidized DNA in human cells is initiated by several DNA glycosylases with overlapping substrate specificity. The human endonuclease VIII homologue NEIL1 removes a broad spectrum of oxidized pyrimidine and purine lesions. In this study of NEIL1 we have identified several key residues, located in three loops lining the DNA binding cavity, important for lesion recognition and DNA glycosylase/AP lyase activity for oxidized bases in double-stranded and single-stranded DNA. Single-turnover kinetics of NEIL1 revealed that removal of 5-hydroxycytosine (5-OHC) and 5-hydroxyuracil (5-OHU) is ∼25 and ∼10-fold faster in duplex DNA compared to single-stranded DNA, respectively, and also faster than removal of dihydrothymine (DHT) and dihydrouracil (DHU), both in double-stranded and single-stranded DNA. NEIL1 excised 8-oxoguanine (8-oxoG) only from double-stranded DNA and analysis of site-specific mutants revealed that Met81, Arg119 and Phe120 are essential for removal of 8-oxoG. Further, several arginine and histidine residues located in the loop connecting the two β-strands forming the zincless finger motif and projecting into the DNA major groove, were shown to be imperative for lesion processing for both single- and double-stranded substrates. Trapping experiments of active site mutants revealed that the N-terminal Pro2 and Lys54 can alternate to form a Schiff-base complex between the protein and DNA. Hence, both Pro2 and Lys54 are involved in the AP lyase activity. While wildtype NEIL1 activity almost exclusively generated a δ-elimination product when processing single-stranded substrates, substitution of Lys54 changed this in favor of a β-elimination product. These results suggest that Pro2 and Lys54 are both essential for the concerted action of the β,δ-elimination in NEIL1.
authors.affiliation: Department of Medical Biochemistry, Clinic for Diagnostics and Intervention, Oslo University Hospital, Oslo, Norway.
authors.forename: Erik Sebastian
authors.initials: ES
authors.lastname: Vik
authors.forename: Ingrun
authors.initials: I
authors.lastname: Alseth
authors.forename: Monika
authors.initials: M
authors.lastname: Forsbring
authors.forename: Ina Høydal
authors.initials: IH
authors.lastname: Helle
authors.forename: Ingrid
authors.initials: I
authors.lastname: Morland
authors.forename: Luisa
authors.initials: L
authors.lastname: Luna
authors.forename: Magnar
authors.initials: M
authors.lastname: Bjørås
authors.forename: Bjørn
authors.initials: B
authors.lastname: Dalhus
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D020134:Catalytic Domain / Q000235:genetics; D018736:DNA Adducts; D045647:DNA Glycosylases / Q000737:chemistry* / Q000235:genetics; D004260:DNA Repair; D004277:DNA, Single-Stranded; D006801:Humans; D008969:Molecular Sequence Data; D012545:Schiff Bases
chemical_list: D018736:DNA Adducts; D004277:DNA, Single-Stranded; D012545:Schiff Bases; D045647:DNA Glycosylases; C473634:NEIL1 protein, human