Homocysteine S-methyltransferases (HMTs, EC 18.104.22.168) catalyse the conversion of homocysteine to methionine using S-methylmethionine or S-adenosylmethionine as the methyl donor. HMTs play an important role in methionine biosynthesis and are widely distributed among micro-organisms, plants and animals. Additionally, HMTs play a role in metabolite repair of S-adenosylmethionine by removing an inactive diastereomer from the pool. The mmuM gene product from Escherichia coli is an archetypal HMT family protein and contains a predicted zinc-binding motif in the enzyme active site. In the present study, we demonstrate X-ray structures for MmuM in oxidized, apo and metallated forms, representing the first such structures for any member of the HMT family. The structures reveal a metal/substrate-binding pocket distinct from those in related enzymes. The presented structure analysis and modelling of co-substrate interactions provide valuable insight into the function of MmuM in both methionine biosynthesis and cofactor repair.
Crystal structure of the homocysteine methyltransferase MmuM from Escherichia coli
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Kunhua Li, Gengnan Li, Louis M.T. Bradbury, Andrew D. Hanson, Steven D. Bruner; Crystal structure of the homocysteine methyltransferase MmuM from Escherichia coli. Biochem J 1 February 2016; 473 (3): 277–284. doi: https://doi.org/10.1042/BJ20150980
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