Download MendeleyHhaI methyltransferase flips its target base out of the DNA helix.
Klimasauskas, S., Kumar, S., Roberts, R.J., Cheng, X.(1994) Cell 76: 357-369
- PubMed: 8293469 Search on PubMed
- DOI: https://doi.org/10.1016/0092-8674(94)90342-5
- Primary Citation Related Structures:
1MHT - PubMed Abstract:
The crystal structure has been determined at 2.8 A resolution for a chemically-trapped covalent reaction intermediate between the HhaI DNA cytosine-5-methyltransferase, S-adenosyl-L-homocysteine, and a duplex 13-mer DNA oligonucleotide containing methylated 5-fluorocytosine at its target. The DNA is located in a cleft between the two domains of the protein and has the characteristic conformation of B-form DNA, except for a disrupted G-C base pair that contains the target cytosine. The cytosine residue has swung completely out of the DNA helix and is positioned in the active site, which itself has undergone a large conformational change. The DNA is contacted from both the major and the minor grooves, but almost all base-specific interactions between the enzyme and the recognition bases occur in the major groove, through two glycine-rich loops from the small domain. The structure suggests how the active nucleophile reaches its target, directly supports the proposed mechanism for cytosine-5 DNA methylation, and illustrates a novel mode of sequence-specific DNA recognition.
- W. M. Keck Structural Biology Laboratory, Cold Spring Harbor, New York 11724.
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