SpeakerProf. Saulius Klimašauskas, Vilnius University, Host: Norbert Reich
Date and LocationWednesday June 06, 2018 11:00am to 12:00pm
Epigenetic states of cytosine, 5-methylcytosine (5mC), 5-hydroxymethylcytosine (hmC), 5-formylcytosine and 5-carboxylcytosine (caC) in CpG dinucleotides are part of an intricate regulation in eukaryote genomes including humans, which contribute to normal phenotypic variation and disease risk. DNA cytosine-5 methyltransferases (C5-MTases), which catalyze the transfer of the methyl group from the ubiquitous cofactor AdoMet to the 5-position of cytosine residues, serve as primary writers of epigenetic DNA marks. Mechanistic studies of both bacterial and mammalian enzymes showed that the reaction requires covalent activation of the cytosine ring by the enzyme before the cofactor-dependent methylation can occur. We redesigned the methyltransferase reaction for the transfer of larger chemical entities by engineering the catalytic center and employing synthetic AdoMet analogs with transferable reporter or functional groups. We also found that the activated cytosine or hmc residues can react with non-cofactor-like compounds such as aldehydes or thiols leading to their further modification; similar enzymatic activation of hmC or caC residues leads to a loss of 5-hydromethyl- or 5-carboxyl groups, respectively, yielding unmodified cytosine in DNA. These novel atypical reactions illustrate a high catalytic plasticity of C5-MTases in vitro and provide plausible chemical precedents in support of possible roles of these enzymes in direct erasure of epigenetic marks in mammalian DNA. The new reactions of C5-MTases enable targeted functionalization and labeling of DNA, which can be used for interrogating the methylation sites in the genome.