Three-Dimensional Structure of the Adenine-Specific DNA Methyltransferase M·Taq I in Complex with the Cofactor S-Adenosylmethionine

• Published in: Proceedings of the National Academy of Sciences - PNAS 1994-11, Vol.91 (23), p.10957-10961
• Main Authors: Labahn, J., Granzin, J., Schluckebier, G., Robinson, D. P., Jack, W. E., Schildkraut, I., Saenger, W.
• Format: Article
• Language: English
• Subjects: Amino acids; Atoms; Biochemistry; Deoxyribonucleic acid; DNA; Electron density; Enzymes; Hydrogen bonds; Molecules; Nucleic acids; Wavelengths
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.91.23.10957

The Thermus aquaticus DNA methyltransferase M·Taq I (EC 2.1.1.72) methylates N6of adenine in the specific double-helical DNA sequence TCGA by transfer of-CH3from the cofactor S-adenosyl-L-methionine. The x-ray crystal structure at 2.4-$\overset{circ}{Mathrm A}$resolution of this enzyme in complex with S-adenosylmethionine shows α/β folding of the polypeptide into two domains of about equal size. They are arranged in the form of a C with a wide cleft suitable to accommodate the DNA substrate. The N-terminal domain is dominated by a nine-stranded β-sheet; it contains the two conserved segments typical for N-methyltransferases which form a pocket for cofactor binding. The C-terminal domain is formed by four small β-sheets and α-helices. The three-dimensional folding of M·Taq I is similar to that of the cytosine-specific Hha I methyltransferase, where the large β-sheet in the N-terminal domain contains all conserved segments and the enzymatically functional parts, and the smaller C-terminal domain is less structured.