Mycinamicins, new macrolide antibiotics. XI. Isolation and structure elucidation of a key intermediate in the biosynthesis of the mycinamicins, mycinamicin VIII.
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The structures of novel macrolide antibiotics, quinolidomicins A1, A2 and B1, were elucidated as shown in Fig. 1 by NMR spectral analysis including a variety of two-dimensional techniques. The quinolidomicins possess a novel 60-membered macrolide ring, which is to our knowledge the largest among natural products.
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The mode of action of the known antifungal macrolides rustmicin (1) and galbonolide B (2) has been determined to be the inhibition of sphingolipid biosynthesis. A large scale fermentation and isolation process was developed for production of large quantities of rustmicin. New 21-hydroxy derivatives of both compounds were isolated from pilot scale fermentations and were also produced by biotransformation of rustmicin and galbonolide B.
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Methylation of G1405 within bacterial 16S ribosomal RNA results in high-level resistance to specific combinations of aminoglycoside antibiotics. Only a few closely related methyltransferases (MTases), which carry out the respective modification (here dubbed "Agr", for aminoglycoside resistance), are known. It is not clear, whether they are related to "typical" S-adenosylmethionine (AdoMet)-dependent MTases or not. Demydchuk et al., 1998 proposed that the cofactor-binding region is localized at the C-terminus of Agr MTases, which implies an interesting case of sequence permutation. Since the Agr MTases lack significant sequence similarity to other proteins, we tested that hypothesis using more sensitive sequence/structure threading approach. Structure prediction confirmed the presence of a putative AdoMet-binding site in these proteins, albeit at a distinct location, resembling that of "typical", non-permuted MTases. Additionally, a small alpha-helical domain dissimilar to other proteins in the database was identified in the N-terminal region of Agr MTases. Comparison of a three-dimensional model of the Agr family member with a recently solved structure of reovirus mRNA capping MTase suggests that the mechanism of guanine-N7 methylation in rRNA and mRNA may be different.
Dilution of the fermentation broths with water before the mycelium separation lowered the specific cake resistance. The effect of the dilution on the filtration duration was different and depended on the fermentation broth type. As for the erythromycin fermentation broth, the time of its filtration decreased after the dilution, while the filtration time of the fermentation broths of the other 2 antibiotic-producing organisms increased after the dilution.
A synthetic medium for biosynthesis of gentamicin was developed. It includes maltose, gelatine, potassium phosphate, ammonium sulphate, cobalt chloride, sodium chloride, magnesium sulphate and zinc sulphate. The dynamics of the biochemical changes in the above medium was studied.
Conditions were experimentally studied for reproducing sisomicin biosynthesis by up-to-down scaling. It was shown that respiration intensity as a parameter of antibiotic biosynthesis scaling-down had certain limitations connected with multistage oxygen mass transfer. The parameter could be used only when the limiting stages of oxygen mass transfer coincided. It was confirmed experimentally that it was possible to apply the previously proposed theoretical method to estimation of the limiting stage of oxygen mass transfer.
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