nanaomycin-a and kalafungin

The ActVA-ActVB system from Streptomyces coelicolor isatwo-component flavin-dependent monooxygenase that belongs to an emerging class of enzymes involved in various oxidation reactions in microorganisms. The ActVB component is a NADH:flavin oxidoreductase that provides a reduced FMN to the second component, ActVA the proper monooxygenase. In this work, we demonstrate that the ActVA-ActVB system catalyzes the aromatic monohydroxylation of dihydrokalafungin by molecular oxygen. In the presence of reduced FMN and molecular oxygen, the ActVA active site accommodates and stabilizes an electrophilic flavin FMN-OOH hydroperoxide intermediate species as the oxidant. Surprisingly, we demonstrate that the quinone form of dihydrokalafungin is not oxidized by the ActVA-ActVB system, whereas the corresponding hydroquinone is an excellent substrate. The enantiomer of dihydrokalafungin, nanaomycin A, as well as the enantiomer of kalafungin, nanaomycin D, are also substrates in their hydroquinone forms. The previously postulated product of the ActVA-ActVB system, the antibiotic actinorhodin, was not found to be formed during the oxidation reaction.

Topics: Anthraquinones; Flavins; FMN Reductase; Hydrogen Peroxide; Hydroquinones; Hydroxylation; Mixed Function Oxygenases; Naphthoquinones; Oxidants; Quinones; Streptomyces coelicolor; Substrate Specificity

Large actI, III-homologous DNA fragments were isolated from genomic libraries of the strains that produce the benzoisochromanequinone antibiotics kalafungin and nanaomycin A methyl ester, Streptomyces tanashiensis strain Kala and Streptomyces sp. OM-173, respectively. These libraries were prepared in Escherichia coli JM108 by using a novel Streptomyces-E. coli bifunctional cosmid, pKU205, and screened with polyketide synthase genes (actI and III) for actinorhodin biosynthesis from Streptomyces coelicolor A3(2) as probes. The cloned DNA fragments (28 and 42 kb) were analyzed by hybridization with DNA containing actinorhodin biosynthetic genes (actI, II, III, IV, VA, VB, VI and VII). Both fragments hybridized with the actI, III, VA and VI regions, but not with the actII, IV, VB and VII regions. The cloned fragment of S. tanashiensis DNA was analyzed by complementation tests with kalafungin-nonproducing mutants. Seven genes (kalI approximately VII), which correspond to seven steps in kalafungin biosynthesis, were found to be located on a 14 kb continuous DNA fragment. Five of the genes were located on the regions homologous to the genes for actinorhodin biosynthesis, but the other two genes were not. Although kalafungin is an intermediate or shunt product in actinorhodin biosynthesis in S. coelicolor A3(2), the genes for kalafungin biosynthesis in S. tanashiensis are not identical with those in S. coelicolor A3(2).

Topics: Anthraquinones; Antifungal Agents; Cloning, Molecular; DNA; Genes, Bacterial; Genomic Library; Hybridization, Genetic; Naphthoquinones; Streptomyces

The site of regulation of nanaomycin biosynthesis by inorganic phosphate was studied with washed cells previously grown in a chemically defined medium containing a high- or low-phosphate concentration. The former mycelia produced only about one-tenth the amount of nanaomycin A from acetate as did the latter mycelia. On the other hand, the bioconversions of nanaomycin D to A and nanaomycin A to E were only slightly affected. It is suggested that the site of regulation of nanaomycin biosynthesis by inorganic phosphate lies within steps between acetate and nanaomycin D.

Topics: Anti-Bacterial Agents; Chemical Phenomena; Chemistry; Culture Media; Hydrogen-Ion Concentration; Naphthoquinones; Phosphates; Streptomyces

Topics: Antifungal Agents; Chromatography, Thin Layer; Fermentation; Molecular Structure; Naphthoquinones; Nocardia; Stereoisomerism

Nanaomycin (NNM) D had a higher growth inhibitory activity than NNM-A against a Gram-negative marine bacterium, Vibrio alginolyticus. These quinone antibiotics were reduced by the respiratory chain-linked flavin dehydrogenase of the organism and the reduced forms of NNMs were quickly autoxidized by molecular oxygen to produce superoxide radicals (O2-). NNM-D was more effective than NNM-A both in the induction of KCN-insensitive oxygen consumption with the intact cells and in the production of O2- by the redox cycling. The growth inhibitory activities of NNM-D and A were partly reduced by raising the superoxide dismutase level of the cells. Thus, the ability to produce O2- at the cell membrane was correlated to the antibacterial activities of NNM-D and A.

Topics: Anti-Bacterial Agents; Electron Transport; NADH Dehydrogenase; Naphthoquinones; Oxygen Consumption; Superoxide Dismutase; Superoxides; Vibrio; Water Microbiology

Nanaomycin D reductase which is involved in the biosynthesis of the antifungal antibiotic nanaomycin catalyzes the formation of nanaomycin A from nanaomycin D in the presence of NADH under anaerobic conditions. On the other hand, under aerobic conditions NADH is consumed and nanaomycin A formation is markedly reduced. These findings suggest that nanaomycin A synthesis is not due to the direct reduction of the 5-membered lactone ring of nanaomycin D. Reduction of various quinones by the enzyme was examined. It was found that nanaomycin A is converted to its hydroquinone derivative in the presence of NADH under anaerobic conditions, whereas NADH consumption alone is observed under aerobic conditions. When p-benzoquinone, 1,4-naphthoquinone or menadione is used instead of nanaomycin D, NADH is also consumed. These results indicate that: (1) these compounds act as electron acceptors, (2) O2 functions as final electron acceptor under aerobic conditions, and (3) nanaomycin D reductase is, in fact, an NADH dehydrogenase (quinone). Changes in the UV-absorption spectrum of a reaction mixture containing nanaomycin D and NADH indicate that a hydroquinone derivative is formed as an intermediate during nanaomycin A formation. Similar results were obtained when nanaomycin D is reduced chemically with NaBH4 or Zn powder. It was concluded that nanaomycin D is converted to a hydroquinone derivative and that nanaomycin A is then formed nonenzymatically through intramolecular electron transfer.

Topics: Aerobiosis; Anaerobiosis; Antifungal Agents; Biotransformation; Chemical Phenomena; Chemistry; Hydroquinones; NADH Dehydrogenase; Naphthoquinones; Oxidation-Reduction; Oxidoreductases

Nanaomycin D reductase, catalyzing the conversion of nanaomycin D to nanaomycin A, which is the first step in the biosynthetic sequence (D leads to A leads to E leads to B) in Streptomyces rosa var. notoensis, was purified from the crude extract of the strain by ammonium sulfate fractionation and column chromatography on DEAE-cellulose, Sephadex G-100 and hydroxyapatite to give an electrophoretically homogeneous preparation. The enzyme was found to be a flavoprotein which contains FAD as a prosthetic group and has a molecular weight of 68,000 daltons. It catalyzed the reductive transformation of nanaomycin D to nanaomycin A in the presence of NADH under anaerobic conditions. The Km values were 250 microM for nanaomycin D and 62 microM for NADH. The enzyme was inhibited by 1 mM Cu2+ ion and by NADH at concentrations over 50 microM. The optimal pH was 5.0 and the optimal temperature was 37 degrees C. Several benzoisochromane-quinone antibiotics other than nanaomycin D, kalafungin (enantiomer of nanaomycin D), griseucin A and frenolicin B were converted to the corresponding reduced products by the enzyme. However, granaticin and 4 alpha, 10 alpha-epoxynanaomycin D were not converted.

Topics: Anti-Bacterial Agents; Hydrogen-Ion Concentration; Kinetics; Molecular Weight; NAD; Naphthoquinones; Oxidoreductases; Spectrum Analysis; Streptomyces; Substrate Specificity; Temperature

The biosynthetic relationship of the nanaomycins produced by Streptomyces rosa var. notoensis OS-3966 was studied by means of a bioconversion method using the antibiotic cerulenin, a specific inhibitor of fatty acid and polyketide biosyntheses. Nanaomycin D was considered to be the first component produced from the hypothetical intermediate "polyketide". It is proposed that the biosynthesis sequence for the nanaomycin is: nanaomycin D leads to nanaomycin A leads to nanaomycin E leads to nanaomycin B. Nanaomycin B can be converted to nanaomycin A by non-enzymatic dehydration; however, nanaomycin A is rapidly bioconverted to nanaomycin E, which is the major component synthesized by the nanaomycin-producing strain.

Topics: Antifungal Agents; Biotransformation; Cerulenin; Fatty Acids; Naphthoquinones; Streptomyces; Time Factors