PMID:7992050
| Citation |
Drennan, CL, Huang, S, Drummond, JT, Matthews, RG and Lidwig, ML (1994) How a protein binds B12: A 3.0 A X-ray structure of B12-binding domains of methionine synthase. Science 266:1669-74 |
|---|---|
| Abstract |
The crystal structure of a 27-kilodalton methylcobalamin-containing fragment of methionine synthase from Escherichia coli was determined at 3.0 A resolution. This structure depicts cobalamin-protein interactions and reveals that the corrin macrocycle lies between a helical amino-terminal domain and an alpha/beta carboxyl-terminal domain that is a variant of the Rossmann fold. Methylcobalamin undergoes a conformational change on binding the protein; the dimethylbenzimidazole group, which is coordinated to the cobalt in the free cofactor, moves away from the corrin and is replaced by a histidine contributed by the protein. The sequence Asp-X-His-X-X-Gly, which contains this histidine ligand, is conserved in the adenosylcobalamin-dependent enzymes methylmalonyl-coenzyme A mutase and glutamate mutase, suggesting that displacement of the dimethylbenzimidazole will be a feature common to many cobalamin-binding proteins. Thus the cobalt ligand, His759, and the neighboring residues Asp757 and Ser810, may form a catalytic quartet, Co-His-Asp-Ser, that modulates the reactivity of the B12 prosthetic group in methionine synthase. |
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| Keywords |
5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase/chemistry; 5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase/metabolism; Amino Acid Isomerases/chemistry; Amino Acid Sequence; Benzimidazoles; Catalysis; Computer Graphics; Crystallography, X-Ray; Electron Spin Resonance Spectroscopy; Escherichia coli/enzymology; Histidine/metabolism; Intramolecular Transferases; Ligands; Methylation; Methylmalonyl-CoA Mutase/chemistry; Models, Molecular; Molecular Sequence Data; Protein Conformation; Protein Folding; Protein Structure, Secondary; Vitamin B 12/analogs & derivatives; Vitamin B 12/chemistry; Vitamin B 12/metabolism |
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