Chemical Diversity of Polyene Macrolides Produced by Streptomyces noursei ATCC 11455 and Recombinant Strain ERD44 with Genetically Altered Polyketide Synthase NysC

Abstract

The gram-positive bacterium Streptomyces noursei ATCC 11455 produces a complex mixture of polyene macrolides generally termed nystatins. Although the structures for nystatins A 1 and A 3 have been reported, the identities of other components of the nystatin complex remain obscure. Analyses of the culture extract from the S. noursei wild type revealed the presence of several nystatin-related compounds for which chemical structures could be suggested on the basis of their molecular weights, their UV spectra, and knowledge of the nystatin biosynthetic pathway. Nuclear magnetic resonance (NMR) studies with one of these polyene macrolides identified it as a nystatin analogue containing a mycarose moiety at C-35. A similar investigation was performed with the culture extract of the ERD44 mutant, which has a genetically altered polyketide synthase (PKS) NysC and which was previously shown to produce a heptaene nystatin analogue. The latter compound, tentatively named S44HP, and its derivative, which contains two deoxysugar moieties, were purified; and their structures were confirmed by NMR analysis. Nystatin analogues with an expanded macrolactone ring were also observed in the extract of the ERD44 mutant, suggesting that the altered PKS can "stutter" during the polyketide chain assembly. These data provide new insights into the biosynthesis of polyene macrolide antibiotics and the functionalities of PKSs and post-PKS modification enzymes.Glycosylated polyene macrolides are very efficient antifungal agents widely used for the treatment of both topical and invasive fungal infections in humans (50). The main advantages of polyene macrolides over other antifungal drugs, such as azoles and flucytosines, are their fungicidal actions and the extremely low incidence of resistant pathogens. The fungicidal actions of polyene macrolide antibiotics are strictly dependent on the presence of sterols in the membranes of the sensitive cells (8). The selective action of these types of antibiotics is based on their higher affinities to the ergosterol present in fungal membranes compared to that of cholesterol, the structural component of mammalian cell membranes. The mode of action of glycosylated polyene macrolides is based on their ability to interact with sterols and to form channels that perforate the membrane, which allows the leakage of ions and other small molecules out of the cell, ultimately resulting in cell death (9). It is presumed that conjugated double bonds present on the macrolactone rings of these molecules (hence the term polyene) are responsible for antibiotic-sterol interactions. Unfortunately, the relatively high toxicities of polyene antibiotics for the mammalian cells and the poor distributions of these compounds in tissues due to low water solubility limit their usefulness for antifungal therapy. Novel polyene antibiotic analogues with reduced toxicities and increased water solubilities might help circumvent these problems.Modification of the antibiotic structure through engineering of its biosynthetic genes is ...

New polyene macrolide family produced by submerged culture of Streptomyces durmitorensis

“…10 In recent years there has been a considerable progress in the genetic analysis and manipulation of producing strains, which led to engineered biosynthesis of several new polyenes used for detailed studies of structure-activity relationships. 11,12 This strategy together with isolation and characterization of new compounds produced by different microorganisms [13][14][15] could result in potential applications in therapy of cancer.…”

Structure elucidation of degradation products of the antibiotic amoxicillin with ion trap MSn and accurate mass determination by ESI TOF

“…Such an instrument is capable of achieving resolving powers of better than 15,000 and mass accuracies in the low single digit ppm range for small molecules [1]. Recently, the implementation of oaTOF instruments for the measurement of accurate molecular mass, the calculation of the empirical formula, and consequently, the identity confirmation of an unknown compound, was impressively demonstrated for a large number of published applications [5][6][7][8][9][10]. For instance, LC/ESI oaTOF was used for the characterization of in vitro drug metabolites by accurate mass measurement of the molecular ion and the CID fragments [5,6].…”

“…The instrument found its place for the quantification and accurate mass measurement of pharmaceutical drugs in plasma [7] as well as for the characterization of trace level impurities in a drug substance [8]. In conjunction with an ion trap instrument for MS/MS and MS 3 experiments to gain structural information, the ESI oaTOF was used for the identification of a photooxygenation product of a broad spectrum antibiotic used for live stock [9] and for the identification of highly complex polyene macrolides isolated from Streptomyces noursei by means of an ion trap monitored purification process [10].…”

Polyene macrolide biosynthesis in streptomycetes and related bacteria: recent advances from genome sequencing and experimental studies

“…The 4, 5 epoxide in pimaricin is formed by the action of a cytochrome P450 on an alkene group. In nystatin, the C35 hydroxyl group may be modified with L-digitoxose or L-mycarose sugars (Bruheim et al, 2004). For a few polyenes, the mycosaminyl residue is modified with a second sugar to form a disaccharide chain (De Poire et al, 2013).…”

“…Lei and co-workers have identified residues in the FscMI that are critical for activity (Lei et al, 2013). Some nystatins and candidins have an additional L-digitoxose or L-mycarose sugar residue attached to C35 (Bruheim et al, 2004;Zielinski et al, 1979) (Fig. 7).…”