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Repair of 1, N 2 ‐ethenoguanine by Alkyladenine DNA Glycosylase
Author(s) -
Thelen Adam,
O’Brien Patrick
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.06001
Subject(s) - dna glycosylase , base excision repair , dna repair , dna , guanine , dna damage , biochemistry , chemistry , cytosine , context (archaeology) , active site , enzyme , gene , biology , nucleotide , paleontology
Human DNA can be damaged by numerous endogenous processes as well as by diverse exogenous factors. The exocyclic amine groups of adenine, cytosine, and guanine can be alkylated by the reactive products of lipid peroxidation or by exposure to vinyl chloride pollutants, leading to the formation of harmful etheno adducts. These etheno lesions can be both mutagenic and cytotoxic, necessitating timely repair. Alkyladenine DNA glycosylase (AAG) has been proposed to initiate the base excision repair of both 1, N 6 ‐ethenoadenine (ɛA) and 1, N 2 ‐ethenoguanine (ɛG). However, examination of the structure of AAG in complex with ɛA‐DNA raises questions about how ɛG could be recognized in an active site optimized for recognition of ɛA. Systematic single and multiple turnover kinetic assays of ɛG excision by AAG reveal that ɛG is recognized far less readily than ɛA in both the natural ɛG:C context as well as in bulges and mispairs. Moreover, AAG is unable to repair ɛG in competition with a large excess of undamaged bases, calling into question how the lesion could be identified in genomic DNA. I hypothesized that the conserved active site residue, Asn169, may play a role in discriminating against the ɛG lesion. Indeed, mutation of Asn169 to Ser results in 7‐fold greater activity toward ɛG. Thus, the conserved active site residues are not optimized for recognition and repair of eG. Together these findings indicate that eG is not a preferred substrate of AAG, and other mechanisms are likely to contribute to eG repair in human cells. Support or Funding Information Funding was provided by a graduate student award from the Department of Biological Chemistry at the University of Michigan, an NSF award MCB‐1615586 (P.J.O), and a fellowship from the Chemistry/Biology Interface Training Program supported by the NIGMS of the NIH under Grant T32GM008597 (A.Z.T.) and R01GM108022 (P.J.O.).