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标题：Oxidative cyclizations in orthosomycin biosynthesis expand the known chemistry of an oxygenase superfamily
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作者：Kathryn M. McCulloch ; Emilianne K. McCranie ; Jarrod A. Smith 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：37
页码：11547-11552
DOI：10.1073/pnas.1500964112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceBacterial resistance to clinically relevant antibiotics has renewed public interest in identifying therapeutics with new scaffolds for the treatment of such infections. Analogs of orthosomycins could provide one such scaffold. One route to modifying these scaffolds is through rational engineering of the biosynthetic enzymes, requiring characterization of the biosynthetic pathway. A key feature of orthosomycin antibiotics is the orthoester linkage between carbohydrate groups, and our data suggest that a family of oxygenases is likely responsible for orthoester formation. Orthosomycins are oligosaccharide antibiotics that include avilamycin, everninomicin, and hygromycin B and are hallmarked by a rigidifying interglycosidic spirocyclic ortho-{delta}-lactone (orthoester) linkage between at least one pair of carbohydrates. A subset of orthosomycins additionally contain a carbohydrate capped by a methylenedioxy bridge. The orthoester linkage is necessary for antibiotic activity but rarely observed in natural products. Orthoester linkage and methylenedioxy bridge biosynthesis require similar oxidative cyclizations adjacent to a sugar ring. We have identified a conserved group of nonheme iron, -ketoglutarate-dependent oxygenases likely responsible for this chemistry. High-resolution crystal structures of the EvdO1 and EvdO2 oxygenases of everninomicin biosynthesis, the AviO1 oxygenase of avilamycin biosynthesis, and HygX of hygromycin B biosynthesis show how these enzymes accommodate large substrates, a challenge that requires a variation in metal coordination in HygX. Excitingly, the ternary complex of HygX with cosubstrate -ketoglutarate and putative product hygromycin B identified an orientation of one glycosidic linkage of hygromycin B consistent with metal-catalyzed hydrogen atom abstraction from substrate. These structural results are complemented by gene disruption of the oxygenases evdO1 and evdMO1 from the everninomicin biosynthetic cluster, which demonstrate that functional oxygenase activity is critical for antibiotic production. Our data therefore support a role for these enzymes in the production of key features of the orthosomycin antibiotics.
关键词：antibiotic biosynthesis ; oxidative cyclization ; crystal structure ; nonheme iron α-ketoglutarate–dependent oxygenases