The biosynthetic gene cluster for the 26-membered ring polyene macrolide pimaricin. A new polyketide synthase organization encoded by two subclusters separated by functionalization genes.
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The biosynthetic gene cluster for the 26-membered ring of the polyene macrolide pimaricin extends for about 110 kilobase pairs of contiguous DNA in the genome of Streptomyces natalensis. Two sets of polyketide synthase (PKS) genes are separated by a group of small polyketide-functionalizing genes. Two of the polyketide synthase genes, pimS0 and pimS1, have been fully sequenced and disrupted proving the involvement of each of these genes in pimaricin biosynthesis. The pimS0 gene encodes a relatively small acetate-activating PKS (approximately 193 kDa) that appears to work as a loading protein which "presents" the starter unit to the second PKS subunit. The pimS1 gene encodes a giant multienzyme (approximately 710 kDa) harboring 15 activities responsible for the first four cycles of chain elongation in pimaricin biosynthesis, resulting in formation of the polyene chromophore. (+info)
Natamycin in genital candidosis in men.
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In a trial of natamycin, an antifungal antibiotic in a vanishing cream base, assessment was possible in 66 men with genital or anal candidosis. The overall cure rate was 82 percent, In 43 patients with culturally proven candidosis it was 98 percent. but in 23 patients treated solely on clinical impression it was only 52 percent. Symptoms were rapidly relieved in those who responded and there were no side-effects. In our hands, natamycin 2 per cent cream has proved to be a valuable preparation in the treatment of candidal balanitis. (+info)
Dematiaceous fungal keratitis. Clinical isolates and management.
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Clinical and laboratory features of 16 cases of keratitis that were caused by dematiaceous pigmented fungi are reported. Management, including the treatment of nine cases with Natamycin (Pimaricin), resulted in corneal healing in 14 cases, and therapeutic surgery in two cases. (+info)
New high-molecular decomposition products of natamycin (pimaricin) with intact lactone-ring.
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Mild acid treatment of natamycin (IV) results in biologically inactive aponatamycin (VI), an amphoteric substance with some natamycin-like chemical and physical properties. Aponatamycin contains one natamycin- and one natamycinolide-moiety. More drastic acid degradation of natamycin eliminates the aminosugar under formation of the dimer (VII) of the hypothetical aglycone of natamycin, natamycinolide (V) as well as a non-ionic compound, the dimer of the 12-decarboxy-11-anhydro analogue of natamycinolide. (+info)
Polyene antibiotics. VII. Carbon-13 nuclear magnetic resonance evidence for cyclic hemiketals in the polyene antibiotics amphotericin B, nystatin A1, tetrin A, tetrin B, lucensomycin, and pimaricin1,2.
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Carbon magnetic resonance establishes conclusively that six polyene macrolide antibiotics containing keto groups (the heptaene amphotericin B, the tetraene-diene nystatin A1, and the tetraenes tetrin A, tetrin B, pimaricin, and lucensomycin) exist in the hemiketal form in solution. Their spectra all contain a hemiketal carbon's absorption near 97 ppm but lack a keto carbon's absorption near 210 ppm. The non-polyenic macrolide erythromycin, on the other hand, exists in the keto form. (+info)
Therapeutic surgery in failures of medical treatment for fungal keratitis.
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Medical treatment failure necessitated surgery in nine cases of fungal keratitis. Therapeutic surgery eliminated fungal infection in seven cases, and useful vision was retained in five out of six penetrating keratoplasties. In three cases Natamycin (Pimaricin) therapy rendered fungi non-viable, but two were demonstrable by histopathology. These results suggest that antifungal treatment should be applied for as long as possible before therapeutic surgery in order to improve the final visual outcome. (+info)
A complex multienzyme system encoded by five polyketide synthase genes is involved in the biosynthesis of the 26-membered polyene macrolide pimaricin in Streptomyces natalensis.
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BACKGROUND: Polyene macrolides are a class of large macrocyclic polyketides that interact with membrane sterols, having antibiotic activity against fungi but not bacteria. Their rings include a chromophore of 3-7 conjugated double bonds which constitute the distinct polyene structure. Pimaricin is an archetype polyene, important in the food industry as a preservative to prevent mould contamination of foods, produced by Streptomyces natalensis. We set out to clone, sequence and analyse the gene cluster responsible for the biosynthesis of this tetraene. RESULTS: A large cluster of 16 open reading frames spanning 84985 bp of the S. natalensis genome has been sequenced and found to encode 13 homologous sets of enzyme activities (modules) of a polyketide synthase (PKS) distributed within five giant multienzyme proteins (PIMS0-PIMS4). The total of 60 constituent active sites, 25 of them on a single enzyme (PIMS2), make this an exceptional multienzyme system. Eleven additional genes appear to govern modification of the polyketide-derived framework and export. Disruption of the genes encoding the PKS abolished pimaricin production. CONCLUSIONS: The overall architecture of the PKS gene cluster responsible for the biosynthesis of the 26-membered polyene macrolide pimaricin has been determined. Eleven additional tailoring genes have been cloned and analysed. The availability of the PKS cluster will facilitate the generation of designer pimaricins by combinatorial biosynthesis approaches. This work represents the extensive description of a second polyene macrolide biosynthetic gene cluster after the one for the antifungal nystatin. (+info)
Engineered biosynthesis of novel polyenes: a pimaricin derivative produced by targeted gene disruption in Streptomyces natalensis.
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BACKGROUND: The post-polyketide synthase biosynthetic tailoring of polyene macrolides usually involves oxidations catalysed by cytochrome P450 monooxygenases (P450s). Although members from this class of enzymes are common in macrolide biosynthetic gene clusters, their specificities vary considerably toward the substrates utilised and the positions of the hydroxyl functions introduced. In addition, some of them may yield epoxide groups. Therefore, the identification of novel macrolide monooxygenases with activities toward alternative substrates, particularly epoxidases, is a fundamental aspect of the growing field of combinatorial biosynthesis. The specific alteration of these activities should constitute a further source of novel analogues. We investigated this possibility by directed inactivation of one of the P450s belonging to the biosynthetic gene cluster of an archetype polyene, pimaricin. RESULTS: A recombinant mutant of the pimaricin-producing actinomycete Streptomyces natalensis produced a novel pimaricin derivative, 4,5-deepoxypimaricin, as a major product. This biologically active product resulted from the phage-mediated targeted disruption of the gene pimD, which encodes the cytochrome P450 epoxidase that converts deepoxypimaricin into pimaricin. The 4,5-deepoxypimaricin has been identified by mass spectrometry and nuclear magnetic resonance following high-performance liquid chromatography purification. CONCLUSIONS: We have demonstrated that PimD is the epoxidase responsible for the conversion of 4,5-deepoxypimaricin to pimaricin in S. natalensis. The metabolite accumulated by the recombinant mutant, in which the epoxidase has been knocked out, constitutes the first designer polyene obtained by targeted manipulation of a polyene biosynthetic gene cluster. This novel epoxidase could prove to be valuable for the introduction of epoxy substituents into designer macrolides. (+info)