title: Methylpurine DNA glycosylase of the hyperthermophilic archaeon Archaeoglobus fulgidus.
abstract: Base excision repair of DNA alkylation damage is initiated by a methylpurine DNA glycosylase (MPG) function. Such enzymes have previously been characterized from bacteria and eukarya, but not from archaea. We identified activity for the release of methylated bases from DNA in cell-free extracts of Archaeoglobus fulgidus, an archaeon growing optimally at 83 degrees C. An open reading frame homologous to the alkA gene of Escherichia coli was overexpressed and identified as a gene encoding an MPG enzyme (M(r) = 34 251), hereafter designated afalkA. The purified AfalkA protein differs from E. coli AlkA by excising alkylated bases only, from DNA, in the following order of efficiency: 3-methyladenine (m(3)A) >> 3-methylguanine approximately 7-methyladenine >> 7-methylguanine. Although the rate of enzymatic release of m(3)A is highest in the temperature range of 65-75 degrees C, it is only reduced by 50% at 45 degrees C, a temperature that does not support growth of A. fulgidus. At temperatures above 75 degrees C, nonenzymatic release of methylpurines predominates. The results suggest that the biological function of AfalkA is to excise m(3)A from DNA at suboptimal and maybe even mesophilic temperatures. This hypothesis is further supported by the observation that the afalkA gene function suppresses the alkylation sensitivity of the E. coli tag alkA double mutant. The amino acid sequence similarity and evolutionary relationship of AfalkA with other MPG enzymes from the three domains of life are described and discussed.
authors.affiliation: Department of Microbiology, University of Bergen, Jahnebakken 5, P.O. Box 7800, N-5020 Bergen, Norway.
authors.forename: Nils-Kåre
authors.initials: NK
authors.lastname: Birkeland
authors.forename: Hilde
authors.initials: H
authors.lastname: Anensen
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Knaevelsrud
authors.forename: Wenche
authors.initials: W
authors.lastname: Kristoffersen
authors.forename: Magnar
authors.initials: M
authors.lastname: Bjørås
authors.forename: Frank T
authors.initials: FT
authors.lastname: Robb
authors.forename: Arne
authors.initials: A
authors.lastname: Klungland
authors.forename: Svein
authors.initials: S
authors.lastname: Bjelland
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000478:Alkylation; D000595:Amino Acid Sequence; D019611:Archaeoglobus fulgidus / Q000201:enzymology* / Q000235:genetics; D002458:Cell Fractionation; D003001:Cloning, Molecular; D045647:DNA Glycosylases; D019175:DNA Methylation; D004260:DNA Repair; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D004794:Enzyme Repression / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification*; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; C025946:3-methyladenine; C021565:3-methyladenine-DNA glycosylase; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; C076131:DNA-3-methyladenine glycosidase II; D000225:Adenine