title: 1,N6-ethenoadenine and 3,N4-ethenocytosine are excised by separate human DNA glycosylases.
abstract: We previously reported our finding that human cells contain glycosylase activity toward all four etheno bases formed in DNA by chloroacetaldehyde and related bi-functional aldehydes. By enzyme purification, including FPLC, we isolated two separate glycosylase activities for 1,N6-ethenoadenine (epsilon A) and for 3,N4-ethenocytosine (epsilon C) respectively, from crude HeLa cell-free extracts, which also contained a number of well-described glycosylases. When Mono-S FPLC purified proteins were assayed against defined oligomers containing either epsilon A or epsilon C, it was found that epsilon A and epsilon C glycosylases were completely separated. It could also be demonstrated that each enzyme bound to and cut only epsilon A- or epsilon C-containing oligomers respectively. There was no overlap in specificity for these two substrates. Several other human glycosylase substrates were also tested and none were cleaved by epsilon C glycosylase. The epsilon C glycosylase activity identified in the present study apparently represents a previously unknown glycosylase. This work also suggests that enzyme recognition of closely related DNA adducts may depend upon subtle changes in local conformation.
authors.affiliation: Life Science Division, Donner Laboratory, Lawrence Berkeley National Laboratory, University of California, Berkeley 94720, USA.
authors.forename: B
authors.initials: B
authors.lastname: Hang
authors.forename: A
authors.initials: A
authors.lastname: Chenna
authors.forename: S
authors.initials: S
authors.lastname: Rao
authors.forename: B
authors.initials: B
authors.lastname: Singer
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000378:metabolism; D001483:Base Sequence; D003596:Cytosine / Q000031:analogs & derivatives* / Q000378:metabolism; D045647:DNA Glycosylases; D004260:DNA Repair; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009153:Mutagens / Q000378:metabolism*; D009699:N-Glycosyl Hydrolases / Q000378:metabolism*
chemical_list: C018289:3,N(4)-ethenocytosine; D009153:Mutagens; C004981:1,N(6)-ethenoadenine; D003596:Cytosine; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D000225:Adenine