title: Domain alternation switches B(12)-dependent methionine synthase to the activation conformation.
abstract: B(12)-dependent methionine synthase (MetH) from Escherichia coli is a large modular protein that uses bound cobalamin as an intermediate methyl carrier. Major domain rearrangements have been postulated to explain how cobalamin reacts with three different substrates: homocysteine, methyltetrahydrofolate and S-adenosylmethionine (AdoMet). Here we describe the 3.0 A structure of a 65 kDa C-terminal fragment of MetH that spans the cobalamin- and AdoMet-binding domains, arranged in a conformation suitable for the methyl transfer from AdoMet to cobalamin that occurs during activation. In the conversion to the activation conformation, a helical domain that capped the cofactor moves 26 A and rotates by 63 degrees, allowing formation of a new interface between cobalamin and the AdoMet-binding (activation) domain. Interactions with the MetH activation domain drive the cobalamin away from its binding domain in a way that requires dissociation of the axial cobalt ligand and, thereby, provide a mechanism for control of the distribution of enzyme conformations.
authors.affiliation: Biophysics Research Division and Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
authors.forename: Vahe
authors.initials: V
authors.lastname: Bandarian
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Pattridge
authors.forename: Brett W
authors.initials: BW
authors.lastname: Lennon
authors.forename: Donald P
authors.initials: DP
authors.lastname: Huddler
authors.forename: Rowena G
authors.initials: RG
authors.lastname: Matthews
authors.forename: Martha L
authors.initials: ML
authors.lastname: Ludwig
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D008958:Models, Molecular; D009068:Movement; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012436:S-Adenosylmethionine / Q000378:metabolism; D014805:Vitamin B 12 / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D012436:S-Adenosylmethionine; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D014805:Vitamin B 12