ATP hydrolysis by the SNF2 domain of the ultraspecific maintenance methylase Dnmt5 drives recognition and modification of hemimethylated DNA

C. neoformans Dnmt5 is an ultraspecific maintenance-type CpG methyltransferase (DNMT) that mediates long-term epigenome evolution. It harbors a DNMT domain and SNF2 ATPase domain. We find that the SNF2 domain couples substrate specificity to an ATPase step that is essential for DNA methylation. Such coupling occurs independently of nucleosomes. Hemimethylated DNA preferentially stimulates ATPase activity, and mutating the Dnmt5 ATP binding pocket disproportionately reduces ATPase stimulation by hemimethylated versus unmethylated substrates. Engineered DNA substrates that stabilize a reaction intermediate by mimicking a ‘flipped-out’ conformation of the target cytosine bypass the SNF2 domain’s requirement for hemimethylation. This result implies that ATP hydrolysis by the SNF2 domain is coupled to base-flipping by the DNMT domain. These findings establish a new role for a SNF2 ATPase domain: controlling substrate recognition and catalysis by an adjoined enzymatic domain. This coupling may contribute to the exquisite specificity of Dnmt5 via mechanisms related to kinetic proofreading.