Domain alternation switches B(12)-dependent methionine synthase to the activation conformation.
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.
Bandarian
Vahe
V
Biophysics Research Division and Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
Pattridge
Katherine A
KA
Lennon
Brett W
BW
Huddler
Donald P
DP
Matthews
Rowena G
RG
Ludwig
Martha L
ML
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
D010446:Peptide Fragments; D012436:S-Adenosylmethionine; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D014805:Vitamin B 12