M.TAQI - POSSIBLE CATALYSIS VIA CATION-PI INTERACTIONS IN N-SPECIFIC DNA METHYLTRANSFERASES

The adenine-specific DNA methyltransferase M.Taql transfers a methyl g roup from S-adenosylmethionine to N6 of the adenine residue in the DNA sequence 5'-TCGA-3', In the crystral structure of M.Taql in complex w ith S-adenosylmethionine the enzyme is folded into two domains: An N-t erminal catalytic domain, whose fold is conserved among S-adenosyl-met hionine dependent methyltransferases, and a DNA recognition domain whi ch possesses a unique fold, In the active site, two aromatic residues, Tyr 108 and Phe 196, are postulated to bind the flipped-out target DN A adenine which becomes methylated, By lowering the energy of the posi tively charged transition state via cationic-pi interactions, these tw o residues probably hold a key role in catalysis.