Reaction: gentamicin X2 + 2 S-adenosyl-L-methionine + reduced acceptor = geneticin + 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 + gentamicin X2 + S-adenosyl-L-methionine = cob(III)alamin + geneticin + 5'-deoxyadenosine + L-methionine
(1c) cob(III)alamin + reduced acceptor = cob(I)alamin + oxidized acceptor
Glossary: geneticin = G418 = (1R,2S,3S,4R,6S)-4,6-diamino-3-{[3-deoxy-4-C-methyl-3-(methylamino)-β-L-arabinopyranosyl]oxy}-2-hydroxycyclohexyl 2-amino-2,7-dideoxy-D-glycero-α-D-gluco-heptopyranoside
Other name(s): genK (gene name); gntK (gene name); gentamicin C-methyltransferase (ambiguous)
Systematic name: S-adenosyl-L-methionine:gentamicin X2 C6'-methyltransferase
Comments: The enzyme, isolated from the bacterium Micromonospora echinospora, has a single [4Fe-4S] cluster per monomer. It is a radical S-adenosyl-L-methionine (SAM) enzyme with 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. It catalyses methylation of the 6'-carbon of gentamicin X2 (GenX2) to produce genetricin (G418) during the biosynthesis of gentamicins. The 6'-pro-R-hydrogen atom of GenX2 is stereoselectively abstracted by the 5'-deoxyadenosyl radical and methylation occurs with retention of configuration at C6'. The regeneration of cob(I)alamin from cob(III)alamin is carried out with an as yet unidentified electron donor.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:
References:
1. Kim, J.Y., Suh, J.W., Kang, S.H., Phan, T.H., Park, S.H. and Kwon, H.J. Gene inactivation study of gntE reveals its role in the first step of pseudotrisaccharide modifications in gentamicin biosynthesis. Biochem Biophys Res Commun 372 (2008) 730-734. [PMID: 18533111]
2. Hong, W. and Yan, L. Identification of gntK, a gene required for the methylation of purpurosamine C-6' in gentamicin biosynthesis. J. Gen. Appl. Microbiol. 58 (2012) 349-356. [PMID: 23149679]
3. Kim, H.J., McCarty, R.M., Ogasawara, Y., Liu, Y.N., Mansoorabadi, S.O., LeVieux, J. and Liu, H.W. GenK-catalyzed C-6' methylation in the biosynthesis of gentamicin: isolation and characterization of a cobalamin-dependent radical SAM enzyme. J. Am. Chem. Soc. 135 (2013) 8093-8096. [PMID: 23679096]
4. Kim, H.J., Liu, Y.N., McCarty, R.M. and Liu, H.W. Reaction catalyzed by GenK, a cobalamin-dependent radical S-adenosyl-l-methionine methyltransferase in the biosynthetic pathway of gentamicin, proceeds with retention of configuration. J. Am. Chem. Soc. 139 (2017) 16084-16087. [PMID: 29091410]