title: Comparative characterization of the lactimidomycin and iso-migrastatin biosynthetic machineries revealing unusual features for acyltransferase-less type I polyketide synthases and providing an opportunity to engineer new analogues.
abstract: Lactimidomycin (LTM, 1) and iso-migrastatin (iso-MGS, 2) belong to the glutarimide-containing polyketide family of natural products. We previously cloned and characterized the mgs biosynthetic gene cluster from Streptomyces platensis NRRL 18993. The iso-MGS biosynthetic machinery featured an acyltransferase (AT)-less type I polyketide synthase (PKS) and three tailoring enzymes (MgsIJK). We now report cloning and characterization of the ltm biosynthetic gene cluster from Streptomyces amphibiosporus ATCC 53964, which consists of nine genes that encode an AT-less type I PKS (LtmBCDEFGHL) and one tailoring enzyme (LtmK). Inactivation of ltmE or ltmH afforded the mutant strain SB15001 or SB15002, respectively, that abolished the production of 1, as well as the three cometabolites 8,9-dihydro-LTM (14), 8,9-dihydro-8S-hydroxy-LTM (15), and 8,9-dihydro-9R-hydroxy-LTM (13). Inactivation of ltmK yielded the mutant strain SB15003 that abolished the production of 1, 13, and 15 but led to the accumulation of 14. Complementation of the ΔltmK mutation in SB15003 by expressing ltmK in trans restored the production of 1, as well as that of 13 and 15. These results support the model for 1 biosynthesis, featuring an AT-less type I PKS that synthesizes 14 as the nascent polyketide intermediate and a cytochrome P450 desaturase that converts 14 to 1, with 13 and 15 as minor cometabolites. Comparative analysis of the LTM and iso-MGS AT-less type I PKSs revealed several unusual features that deviate from those of the collinear type I PKS model. Exploitation of the tailoring enzymes for 1 and 2 biosynthesis afforded two analogues, 8,9-dihydro-8R-hydroxy-LTM (16) and 8,9-dihydro-8R-methoxy-LTM (17), that provided new insights into the structure-activity relationship of 1 and 2. While 12-membered macrolides, featuring a combination of a hydroxyl group at C-17 and a double bond at C-8 and C-9 as found in 1, exhibit the most potent activity, analogues with a single hydroxyl or methoxy group at C-8 or C-9 retain most of the activity whereas analogues with double substitutions at C-8 and C-9 lose significant activity.
authors.affiliation: Division of Pharmaceutical Sciences, University of Wisconsin-Madison , Madison, Wisconsin 53705, United States.
authors.forename: Jeong-Woo
authors.initials: JW
authors.lastname: Seo
authors.forename: Ming
authors.initials: M
authors.lastname: Ma
authors.forename: Thomas
authors.initials: T
authors.lastname: Kwong
authors.forename: Jianhua
authors.initials: J
authors.lastname: Ju
authors.forename: Si-Kyu
authors.initials: SK
authors.lastname: Lim
authors.forename: Hui
authors.initials: H
authors.lastname: Jiang
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Lohman
authors.forename: Chunying
authors.initials: C
authors.lastname: Yang
authors.forename: John
authors.initials: J
authors.lastname: Cleveland
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Zazopoulos
authors.forename: Chris M
authors.initials: CM
authors.lastname: Farnet
authors.forename: Ben
authors.initials: B
authors.lastname: Shen
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D019149:Bioreactors; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D015195:Drug Design; D020868:Gene Silencing; D006801:Humans; D018942:Macrolides / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D008954:Models, Biological; D008969:Molecular Sequence Data; D015394:Molecular Structure; D005810:Multigene Family; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy; D010881:Piperidones / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D048630:Polyketide Synthases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D061065:Polyketides / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D015202:Protein Engineering; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013237:Stereoisomerism; D013302:Streptomyces / Q000201:enzymology* / Q000235:genetics; D013329:Structure-Activity Relationship
chemical_list: D000903:Antibiotics, Antineoplastic; D001426:Bacterial Proteins; D018942:Macrolides; D050505:Mutant Proteins; D010881:Piperidones; D061065:Polyketides; D011994:Recombinant Proteins; C455261:isomigrastatin; C077633:lactimidomycin; D048630:Polyketide Synthases