Schluckebier G, Labahn J, Granzin J, Saenger W
Institut für Kristallographie, Freie Universität Berlin, Germany.
Biol Chem. 1998 Apr-May;379(4-5):389-400.
The adenine-specific DNA methyltransferase M.TaqI transfers a methyl group from S-adenosylmethionine to N6 of the adenine residue in the DNA sequence 5'-TCGA-3'. In the crystal structure of M.TaqI in complex with S-adenosylmethionine the enzyme is folded into two domains: An N-terminal catalytic domain, whose fold is conserved among S-adenosyl-methionine dependent methyltransferases, and a DNA recognition domain which possesses a unique fold. In the active site, two aromatic residues, Tyr 108 and Phe 196, are postulated to bind the flipped-out target DNA adenine which becomes methylated. By lowering the energy of the positively charged transition state via cationic-pi interactions, these two residues probably hold a key role in catalysis.
腺嘌呤特异性DNA甲基转移酶M.TaqI将一个甲基从S-腺苷甲硫氨酸转移至DNA序列5'-TCGA-3'中腺嘌呤残基的N6位。在M.TaqI与S-腺苷甲硫氨酸复合物的晶体结构中，该酶折叠成两个结构域：一个N端催化结构域，其折叠在依赖S-腺苷甲硫氨酸的甲基转移酶中是保守的；以及一个具有独特折叠的DNA识别结构域。在活性位点，假定两个芳香族残基Tyr 108和Phe 196结合翻转出的、会被甲基化的目标DNA腺嘌呤。通过阳离子-π相互作用降低带正电过渡态的能量，这两个残基可能在催化中起关键作用。
