Reaction: 2 S-adenosyl-L-methionine + cytidine 5'-{[hydroxy(2-hydroxyethyl)phosphonoyl]phosphate} + reduced acceptor = S-adenosyl-L-homocysteine + 5'-deoxyadenosine + L-methionine + cytidine 5'-({hydroxy[(S)-2-hydroxypropyl]phosphonoyl}phosphate) + oxidized acceptor (overall reaction)
(1a) S-adenosyl-L-methionine + cob(I)alamin = S-adenosyl-L-homocysteine + methylcob(III)alamin
(1b) methylcob(III)alamin + cytidine 5'-{[hydroxy(2-hydroxyethyl)phosphonoyl]phosphate} + S-adenosyl-L-methionine = cob(III)alamin + cytidine 5'-({hydroxy[(S)-2-hydroxypropyl]phosphonoyl}phosphate) + 5'-deoxyadenosine + L-methionine
(1c) cob(III)alamin + reduced acceptor = cob(I)alamin + oxidized acceptor
Other name(s): Fom3; S-adenosyl-L-methionine:methylcob(III)alamin:2-hydroxyethylphosphonate methyltransferase (incorrect); 2-hydroxyethylphosphonate methyltransferase (incorrect)
Systematic name: S-adenosyl-L-methionine:cytidine 5'-{[hydroxy(2-hydroxyethyl)phosphonoyl]phosphate} C2-methyltransferase
Comments: Requires cobalamin. The enzyme, isolated from the bacterium Streptomyces wedmorensis, is involved in fosfomycin biosynthesis. It is a radical S-adenosyl-L-methionine (SAM) enzyme that contains a [4Fe-4S] center and a methylcob(III)alamin cofactor. The enzyme uses two molecues of SAM for the reaction. One molecule forms a 5'-deoxyadenosyl radical, while the other is used to methylate the cobalamin cofactor. The 5'-deoxyadenosyl radical abstracts a hydrogen from the C2 position of cytidine 5'-{[(2-hydroxyethyl)phosphonoyl]phosphate} forming a free radical that reacts with the methyl group on methylcob(III)alamin at the opposite side from SAM and the [4Fe-4S] cluster with inversion of configuration to produce the (S)-isomer of the methylated product and cob(II)alamin. Both the [4Fe-4S] cluster and the cob(II)alamin need to be reduced by an unknown factor(s) before the enzyme could catalyse another cycle.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Woodyer, R.D., Li, G., Zhao, H. and van der Donk, W.A. New insight into the mechanism of methyl transfer during the biosynthesis of fosfomycin. Chem. Commun. (Camb.) (2007) 359-361. [PMID: 17220970]
2. Allen, K.D. and Wang, S.C. Initial characterization of Fom3 from Streptomyces wedmorensis: The methyltransferase in fosfomycin biosynthesis. Arch. Biochem. Biophys. 543 (2014) 67-73. [PMID: 24370735]
3. Sato, S., Kudo, F., Kim, S.Y., Kuzuyama, T. and Eguchi, T. Methylcobalamin-dependent radical SAM C-methyltransferase Fom3 recognizes cytidylyl-2-hydroxyethylphosphonate and catalyzes the nonstereoselective C-methylation in fosfomycin biosynthesis. Biochemistry 56 (2017) 3519-3522. [PMID: 28678474]
4. Blaszczyk, A.J. and Booker, S.J. A (re)discovery of the Fom3 substrate. Biochemistry 57 (2018) 891-892. [PMID: 29345912]
5. Sato, S., Kudo, F., Kuzuyama, T., Hammerschmidt, F. and Eguchi, T. C-methylation catalyzed by Fom3, a cobalamin-dependent radical S-adenosyl-L-methionine enzyme in fosfomycin biosynthesis, proceeds with inversion of configuration. Biochemistry 57 (2018) 4963-4966. [PMID: 29966085]