How a protein binds B12: A 3.0 A X-ray structure of B12-binding domains of methionine synthase.Drennan, C.L., Huang, S., Drummond, J.T., Matthews, R.G., Ludwig, M.L.
(1994) Science 266: 1669-1674
- PubMed: 7992050
- DOI: https://doi.org/10.1126/science.7992050
- Primary Citation of Related Structures:
- PubMed 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.
Biophysics Research Division, University of Michigan, Ann Arbor 48109-1055.