Reaction: (1) (2R,3R,5S)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + 2 S-adenosyl-L-methionine + reduced acceptor = (2R,3R,5S,6R)-6-(methyl)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + 5'-deoxyadenosine + L-methionine + S-adenosyl-L-homocysteine + oxidized acceptor (overall reaction)
(1a) S-adenosyl-L-methionine + cob(I)alamin = S-adenosyl-L-homocysteine + methylcob(III)alamin
(1b) methylcob(III)alamin + (2R,3R,5S)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + S-adenosyl-L-methionine = cob(III)alamin + (2R,3R,5S,6R)-6-(methyl)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + 5'-deoxyadenosine + L-methionine
(1c) cob(III)alamin + reduced acceptor = cob(I)alamin + oxidized acceptor
(2) (2R,3R,5S,6R)-6-(methyl)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + 2 S-adenosyl-L-methionine + reduced acceptor = (2R,3R,5S,6R)-6-(ethyl)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + 5'-deoxyadenosine + L-methionine + S-adenosyl-L-homocysteine + oxidized acceptor (overall reaction)
(2a) S-adenosyl-L-methionine + cob(I)alamin = S-adenosyl-L-homocysteine + methylcob(III)alamin
(2b) methylcob(III)alamin + (2R,3R,5S,6R)-6-(methyl)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + S-adenosyl-L-methionine = cob(III)alamin + (2R,3R,5S,6R)-6-(ethyl)-2-(S-pantetheinyl)-carbapenam-3-carboxylate + 5'-deoxyadenosine + L-methionine
(2c) cob(III)alamin + reduced acceptor = cob(I)alamin + oxidized acceptor
Other name(s): thnK (gene name)
Systematic name: S-adenosyl-L-methionine:(2R,3R,5S)-2-(S-pantetheinyl)-carbapenam-3-carboxylate 6-C-methyltransferase
Comments: A radical SAM (AdoMet) enzyme that catalyses two consecutive methylations during the biosynthesis of complex carbapenem antibiotics. The enzyme adds a methyl group at position 6, followed by a second methylation that converts the methyl group to an ethyl group. The enzyme binds a [4Fe-4S] cluster and requires a cobalamin cofactor and an electron donor. Methyl viologen can be used in vitro.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Marous, D.R., Lloyd, E.P., Buller, A.R., Moshos, K.A., Grove, T.L., Blaszczyk, A.J., Booker, S.J. and Townsend, C.A. Consecutive radical S-adenosylmethionine methylations form the ethyl side chain in thienamycin biosynthesis. Proc. Natl. Acad. Sci. USA 112 (2015) 10354-10358. [PMID: 26240322]
2. Sinner, E.K. and Townsend, C.A. Purification and characterization of sequential cobalamin-dependent radical SAM methylases ThnK and TokK in carbapenem β-lactam antibiotic biosynthesis. Methods Enzymol. 669 (2022) 29-44. [PMID: 35644176]