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. 1994 Jan 28;76(2):357-69.
doi: 10.1016/0092-8674(94)90342-5.

HhaI methyltransferase flips its target base out of the DNA helix

S Klimasauskas  1 , S Kumar, R J Roberts, X Cheng
Affiliations

HhaI methyltransferase flips its target base out of the DNA helix

S Klimasauskas et al. Cell. .

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.

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Comment in

  • The flip side of DNA methylation.
    Verdine GL. Verdine GL. Cell. 1994 Jan 28;76(2):197-200. doi: 10.1016/0092-8674(94)90326-3. Cell. 1994. PMID: 8293456 Review. No abstract available.

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