Structural dynamics of double-stranded DNA with epigenome modification

Modification of cytosine plays an important role in epigenetic regulation of gene expression and genome stability. Cytosine is converted to 5-methylcytosine (5mC) by DNA methyltransferase; in turn, 5mC may be oxidized to 5-hydroxymethylcytosine (5hmC) by ten-eleven translocation enzyme. The structural flexibility of DNA is known to affect the binding of proteins to methylated DNA. Here, we have carried out a semi-quantitative analysis of the dynamics of double-stranded DNA (dsDNA) containing various epigenetic modifications by combining data from imino (1)H exchange and imino (1)H R(1ρ) relaxation dispersion NMR experiments in a complementary way. Using this approach, we characterized the base-opening (k(open)) and base-closing (k(close)) rates, facilitating a comparison of the base-opening and -closing process of dsDNA containing cytosine in different states of epigenetic modification. A particularly striking result is the increase in the k(open) rate of hemi-methylated dsDNA 5mC/C relative to unmodified or fully methylated dsDNA, indicating that the Watson–Crick base pairs undergo selective destabilization in 5mC/C. Collectively, our findings imply that the epigenetic modulation of cytosine dynamics in dsDNA mediates destabilization of the GC Watson–Crick base pair to allow base-flipping in living cells.