1mht
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COVALENT TERNARY STRUCTURE OF HHAI METHYLTRANSFERASE, DNA AND S-ADENOSYL-L-HOMOCYSTEINE
OverviewOverview
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.
About this StructureAbout this Structure
1MHT is a Single protein structure of sequence from Haemophilus haemolyticus with as ligand. Active as Deleted entry, with EC number 2.1.1.73 Full crystallographic information is available from OCA.
ReferenceReference
HhaI methyltransferase flips its target base out of the DNA helix., Klimasauskas S, Kumar S, Roberts RJ, Cheng X, Cell. 1994 Jan 28;76(2):357-69. PMID:8293469
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