title: Biosynthesis of HSAF, a tetramic acid-containing macrolactam from Lysobacter enzymogenes.
abstract: HSAF was isolated from Lysobacter enzymogenes , a bacterium used in the biological control of fungal diseases of plants. Structurally, it is a tetramic acid-containing macrolactam fused to a tricyclic system. HSAF exhibits a novel mode of action by disrupting sphingolipids important to the polarized growth of filamentous fungi. Here we describe the HSAF biosynthetic gene cluster, which contains only a single-module polyketide synthase/nonribosomal peptide synthetase (PKS/NRPS), although the biosynthesis of HSAF apparently requires two separate polyketide chains that are linked together by one amino acid (ornithine) via two amide bonds. Flanking the PKS/NRPS are six genes that encoding a cascade of four tightly clustered redox enzymes on one side and a sterol desaturase/fatty acid hydroxylase and a ferredoxin reductase on the other side. The genetic data demonstrate that the four redox genes, in addition to the PKS/NRPS gene and the sterol desaturase/fatty acid hydroxylase gene, are required for HSAF production. The biochemical data show that the adenylation domain of the NRPS specifically activates L-ornithine and that the four-domain NRPS is able to catalyze the formation of a tetramic acid-containing product from acyl-S-ACP and ornithinyl-S-NRPS. These results reveal a previously unrecognized biosynthetic mechanism for hybrid PK/NRP in prokaryotic organisms.
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States.
authors.forename: Lili
authors.initials: L
authors.lastname: Lou
authors.forename: Guoliang
authors.initials: G
authors.lastname: Qian
authors.forename: Yunxuan
authors.initials: Y
authors.lastname: Xie
authors.forename: Jiliang
authors.initials: J
authors.lastname: Hang
authors.forename: Haotong
authors.initials: H
authors.lastname: Chen
authors.forename: Kathia
authors.initials: K
authors.lastname: Zaleta-Rivera
authors.forename: Yaoyao
authors.initials: Y
authors.lastname: Li
authors.forename: Yuemao
authors.initials: Y
authors.lastname: Shen
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Dussault
authors.forename: Fengquan
authors.initials: F
authors.lastname: Liu
authors.forename: Liangcheng
authors.initials: L
authors.lastname: Du
mesh_terms: D000935:Antifungal Agents / Q000737:chemistry* / Q000378:metabolism*; D047029:Lactams, Macrocyclic / Q000737:chemistry* / Q000378:metabolism*; D053528:Lysobacter / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D005810:Multigene Family; D010453:Peptide Synthases / Q000235:genetics / Q000378:metabolism; D048630:Polyketide Synthases / Q000235:genetics / Q000378:metabolism; D011760:Pyrrolidinones / Q000737:chemistry*
chemical_list: D000935:Antifungal Agents; C557945:HSAF compound; D047029:Lactams, Macrocyclic; D011760:Pyrrolidinones; C009435:tetramic acid; D048630:Polyketide Synthases; D010453:Peptide Synthases; C104385:non-ribosomal peptide synthase