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. Author manuscript; available in PMC: 2009 Dec 1.
Published in final edited form as: Curr Opin Struct Biol. 2008 Dec;18(6):658–666. doi: 10.1016/j.sbi.2008.11.005

TABLE 1.

CORRINOID-DEPENDENT METHYLTRANSFERASES

Enzyme complex Protein designation Organism Reference
Methionine synthase MetH Escherichia coli Homo sapiens [1]
Coenzyme M methyltransferases
 monomethylamine:CoM MtmBCA Methanosarcina barkeri [40,41]
 dimethylamine:CoM MtbB1CA Methanosarcina barkeri [42]
 trimethylamine:CoM MttB1CA Methanosarcina barkeri [43]
 methanol:CoM MtaBCA Methanosarcina barkeri [25]
 dimethylsulfide:CoM MtsAB Methanosarcina barkeri [44]
 tetramethylammonium:CoM MtqBCA Methanococcoides sp. [45]
Energy-conserving methyltetrahydromethanopterin: coenzyme M methyltransferase MtrA-H Methanobacterium thermoautotrophicum [46]
Veratrol:H4folate O-demethylase OdmABCD Acetobacterium dehalogenans [47,48]
Vanillate:H4folate O-methyltransferase MtvABC Moorella thermoaceticum [49]
AcylCoA synthase/CO dehydrogenase AcsABCDE Moorella thermoaceticum [20]
Methylchloride:H4folate methyltransferase CmuAB Methylobacterium sp. [50]

graphic file with name nihms83618u1.jpg

Methyl groups are transferred as carbocations from the cofactor to acceptor substrates, which are typically thiols such as homocysteine or coenzyme M (ethanethiol sulfonate), leaving the pair of electrons that formed the methyl-carbon bond of the cofactor so that the cobalt is now formally in the +1 oxidation state. The donor substrate then transfers a methyl group to the cofactor, reforming methylcobalamin. Substrate-binding components of these complexes may be either separate proteins, or modules of a protein that also contains the corrinoid-binding domain. Where structures of these substrate-binding components have been determined, they are TIM (α8β8) barrels (e.g. the homocysteine- and methyltetrahydrofolate-binding domains of methionine synthase [5]; the methyltetrahydrofolate-corrinoid-iron/sulfur protein methyltransferase that transfers methyl groups to the corrinoid-iron/sulfur protein [20]; the MtaB component of the methanol-coenzyme M methyltransferase from Methanosarcina barkeri [27••]; and the methylamine-binding domain (MtmB) of the monomethylamine:coenzyme M methyltransferase [28]).