title: Specificity and promiscuity at the branch point in gentamicin biosynthesis.
abstract: Gentamicin C complex is a mixture of aminoglycoside antibiotics used to treat severe Gram-negative bacterial infections. We report here key features of the late-stage biosynthesis of gentamicins. We show that the intermediate gentamicin X2, a known substrate for C-methylation at C-6' to form G418 catalyzed by the radical SAM-dependent enzyme GenK, may instead undergo oxidation at C-6' to form an aldehyde, catalyzed by the flavin-linked dehydrogenase GenQ. Surprisingly, GenQ acts in both branches of the pathway, likewise oxidizing G418 to an analogous ketone. Amination of these intermediates, catalyzed mainly by aminotransferase GenB1, produces the known intermediates JI-20A and JI-20B, respectively. Other pyridoxal phosphate-dependent enzymes (GenB3 and GenB4) act in enigmatic dehydroxylation steps that convert JI-20A and JI-20B into the gentamicin C complex or (GenB2) catalyze the epimerization of gentamicin C2a into gentamicin C2.
authors.affiliation: Key Laboratory of Combinatorial Biosynthesis and Drug Discovery (Ministry of Education), and School of Pharmaceutical Sciences, Wuhan University, Wuhan, Wuchang 430071, People's Republic of China.
authors.forename: Junhong
authors.initials: J
authors.lastname: Guo
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK.
authors.forename: Fanglu
authors.initials: F
authors.lastname: Huang
authors.affiliation: Key Laboratory of Combinatorial Biosynthesis and Drug Discovery (Ministry of Education), and School of Pharmaceutical Sciences, Wuhan University, Wuhan, Wuchang 430071, People's Republic of China.
authors.forename: Chuan
authors.initials: C
authors.lastname: Huang
authors.affiliation: Key Laboratory of Combinatorial Biosynthesis and Drug Discovery (Ministry of Education), and School of Pharmaceutical Sciences, Wuhan University, Wuhan, Wuchang 430071, People's Republic of China.
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Duan
authors.affiliation: Key Laboratory of Combinatorial Biosynthesis and Drug Discovery (Ministry of Education), and School of Pharmaceutical Sciences, Wuhan University, Wuhan, Wuchang 430071, People's Republic of China.
authors.forename: Xinyun
authors.initials: X
authors.lastname: Jian
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK.
authors.forename: Finian
authors.initials: F
authors.lastname: Leeper
authors.affiliation: Key Laboratory of Combinatorial Biosynthesis and Drug Discovery (Ministry of Education), and School of Pharmaceutical Sciences, Wuhan University, Wuhan, Wuchang 430071, People's Republic of China.
authors.forename: Zixin
authors.initials: Z
authors.lastname: Deng
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK. Electronic address: pfl10@cam.ac.uk.
authors.forename: Peter F
authors.initials: PF
authors.lastname: Leadlay
authors.affiliation: Key Laboratory of Combinatorial Biosynthesis and Drug Discovery (Ministry of Education), and School of Pharmaceutical Sciences, Wuhan University, Wuhan, Wuchang 430071, People's Republic of China. Electronic address: yhsun@whu.edu.cn.
authors.forename: Yuhui
authors.initials: Y
authors.lastname: Sun
mesh_terms: D055162:Biocatalysis; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D005839:Gentamicins / Q000096:biosynthesis* / Q000737:chemistry; D008780:Methyltransferases / Q000378:metabolism*; D008969:Molecular Sequence Data; D013379:Substrate Specificity
chemical_list: D005839:Gentamicins; D008780:Methyltransferases
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