Supplementary material from "Excision of the doubly methylated base <i>N</i>4,5-dimethylcytosine from DNA by <i>Escherichia coli</i> Nei and Fpg proteins"

Published on 2018-03-29T10:15:07Z (GMT) by
Cytosine (C) in DNA is often modified to 5-methylcytosine (m<sup>5</sup>C) to execute important cellular functions. Despite the significance of m<sup>5</sup>C for epigenetic regulation in mammals, damage to m<sup>5</sup>C has received little attention. For instance, almost no studies exist on erroneous methylation of m<sup>5</sup>C by alkylating agents to doubly or triply methylated bases. Owing to chemical evidence, and because many prokaryotes express methyltransferases able to convert m<sup>5</sup>C into <i>N</i><sup>4</sup>,5-dimethylcytosine (m<i><sup>N</sup></i><sup>4,5</sup>C) in DNA, m<i><sup>N</sup></i><sup>4,5</sup>C is probably present <i>in vivo</i>. We screened a series of glycosylases from prokaryotic to human and found significant DNA incision activity of the <i>Escherichia coli</i> Nei and Fpg proteins at m<i><sup>N</sup></i><sup>4,5</sup>C residues <i>in vitro</i>. The activity of Nei was highest opposite cognate guanine followed by adenine, thymine (T) and C. Fpg-complemented Nei by exhibiting the highest activity opposite C followed by lower activity opposite T. To our knowledge, this is the first description of a repair enzyme activity at a further methylated m<sup>5</sup>C in DNA, as well as the first alkylated base allocated as a Nei or Fpg substrate. Based on our observed high sensitivity to nuclease S1 digestion, we suggest that m<i><sup>N</sup></i><sup>4,5</sup>C occurs as a disturbing lesion in DNA and that Nei may serve as a major DNA glycosylase in <i>E. coli</i> to initiate its repair.This article is part of a discussion meeting issue ‘Frontiers in epigenetic chemical biology’.

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Alexeeva, Marina; Guragain, Prashanna; Tesfahun, Almaz N.; Tomkuvienė, Miglė; Arshad, Aysha; Gerasimaitė, Rūta; Rukšėnaitė, Audronė; Urbanavičiūtė, Giedrė; Bjørås, Magnar; K. Laerdahl, Jon; Klungland, Arne; Klimašauskas, Saulius; Bjelland, Svein (2018): Supplementary material from "Excision of the doubly methylated base N4,5-dimethylcytosine from DNA by Escherichia coli Nei and Fpg proteins". The Royal Society. Collection.