Insights into the reactivation of cobalamin-dependent methionine synthase
| Autor: | Markos Koutmos, Katherine A. Pattridge, Janet L. Smith, Supratim Datta, Rowena G. Matthews |
|---|---|
| Rok vydání: | 2009 |
| Předmět: |
Models
Molecular Homocysteine Flavodoxin Stereochemistry 5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase Models Biological Cobalamin Protein Structure Secondary Cofactor chemistry.chemical_compound Catalytic Domain Escherichia coli medicine Methionine synthase Multidisciplinary Methionine biology Spectrum Analysis Cobalt Meth Biological Sciences S-Adenosylhomocysteine Enzyme Activation Vitamin B 12 Amino Acid Substitution chemistry Mutation Methylcobalamin biology.protein Oxidation-Reduction medicine.drug |
| Zdroj: | Proceedings of the National Academy of Sciences. 106:18527-18532 |
| ISSN: | 1091-6490 0027-8424 |
| DOI: | 10.1073/pnas.0906132106 |
| Popis: | Cobalamin-dependent methionine synthase (MetH) is a modular protein that catalyzes the transfer of a methyl group from methyltetrahydrofolate to homocysteine to produce methionine and tetrahydrofolate. The cobalamin cofactor, which serves as both acceptor and donor of the methyl group, is oxidized once every ≈2,000 catalytic cycles and must be reactivated by the uptake of an electron from reduced flavodoxin and a methyl group from S -adenosyl-L-methionine (AdoMet). Previous structures of a C-terminal fragment of MetH (MetH CT ) revealed a reactivation conformation that juxtaposes the cobalamin- and AdoMet-binding domains. Here we describe 2 structures of a disulfide stabilized MetH CT ( s-s MetH CT ) that offer further insight into the reactivation of MetH. The structure of s-s MetH CT with cob(II)alamin and S -adenosyl-L-homocysteine represents the enzyme in the reactivation step preceding electron transfer from flavodoxin. The structure supports earlier suggestions that the enzyme acts to lower the reduction potential of the Co(II)/Co(I) couple by elongating the bond between the cobalt and its upper axial water ligand, effectively making the cobalt 4-coordinate, and illuminates the role of Tyr-1139 in the stabilization of this 4-coordinate state. The structure of s-s MetH CT with aquocobalamin may represent a transient state at the end of reactivation as the newly remethylated 5-coordinate methylcobalamin returns to the 6-coordinate state, triggering the rearrangement to a catalytic conformation. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|