Abstract
Mayamycin B, a new antibacterial type II polyketide, together with its known congener mayamycin A, were isolated from Streptomyces sp. 120454. The structure of new compound was elucidated by extensive spectroscopic analysis and comparison with literature data. Sequencing and bioinformatics analysis revealed the biosynthetic gene cluster for mayamycins A and B.
Natural products biosynthesized by type II polyketide synthases (PKSs) comprise many important clinical drugs or drug candidates [1]. The angucycline-type polycyclic compounds, representing one of the largest family of type II polyketides, features a characteristic tetracyclic benz[a]anthracene scaffold, which are derived via successive decarboxylative Claisen condensations of an acetyl-CoA starter unit and nine methylmalonyl-CoA extender units [2,3,4]. The glycosylation using a combination of diverse sugar units at different angucyline aglycone position creates a great structural diversity for angucycline-type compounds [2, 5, 6]. These include landomycins, urdamycins, and saquayamycin, which are well known for their unusual structural features and potent antibacterial or antitumor bioactivities [7,8,9].
During our effort to discover new/bioactive natural products from microbes, we found that S. sp. 120454 strain mainly produce two major peaks based on chemical profiling when using B medium (dextrin 40 g, tomato paste 7.5 g, NZ Amine 2.5 g, primary yeast 5 g in 1 L distilled water) as fermentation medium. The large-scale fermentation was carried out at 30 °C for 7 days. The broth was harvested, and extracted by ethyl acetate, yielding 3.62 g brown crude extract, which was then fractionated and purified to afford compounds 1 and 2 (Fig. 1).
Compound 1 was isolated as a brown amorphous solid with the molecular formula of C25H23NO7, as determined by high-resolution ESIMS ([M+H]+ m/z = 450.1497), indicating 15° of unsaturation. Initial interpretation of its MS, 1H, 13C NMR spectra (Table 1) indicated the structure of 1 was highly similar to mayamycin (2), an aguacycline-type compound firstly isolated from a marine Streptomyces strain [10], with the exception of lacking an N-methyl group on its aminosugar moiety. Further elucidation of the 1D and 2D NMR spectra confirmed the presence of an identical anguacycline aglycone to that in mayamycin (2). An aminosugar moiety was evident by 1H-1H COSY correlations of H-1′/H-2′/H-3′/H-4′/H-5′/H-6′ from its 1H-1H COSY spectrum, and HMBC correlation of H-5′ (δH 3.56) with C-1′ (δC 72.5); as well as the NMR data comparison with those in 2. The linkage of this aminosugar moiety to angucycline was through a rare C–C bond according to the HMBC correlations of H-1′ with C-4a and C-6.
The stereochemistry of the sugar moiety was determined by interpretation of its NOESY spectrum and J-coupling constant. A large coupling constant (10.2 Hz) between H-1′ and H-2′a indicated an axial configuration of H-1′. The strong NOE correlations of H-1′ with H-3′ and H-5′ revealed that all of these three protons are in axial positions. Furthermore, H-4′ showed NOE correlations to H-2′a suggested that H-4′ and H-2′a are also in axial position. Thus, the relative configuration of the deduced aminosugar is 1′R*, 3′R*, 4′S, and 5′R. The result indicates that compound 1 is an N-desmethyl derivative of mayamycin (2), accordingly, compound 1 is designated as mayamycin B (Fig. 2).
Compound 2 was also isolated as a brown amorphous solid, its structure is identified as mayamycin based on the comparison of its NMR and HRESIMS data with the published data [10, 11].
Mayamycin has been reported to show antibacterial activities against a panel of pathogenic bacteria [10, 11]. Therefore, the antimicrobial activities of compounds 1 and 2 were tested against six pathogenic bacteria as shown in Table 2. The result showed mayamycin B (1) showed potent bioactivity against Micrococcus luteus with MIC value of 2.0 μM, whereas, its congener mayamycin A (2) only has MIC value of 8.0 μM, suggesting the N-methyl group is important to its activity.
We next aimed to identify mayamycin biosynthetic gene cluster. To facilitate the process, the strain of Streptomyces sp. 120454 was subjected to whole-genome sequencing by Pacbio, yielding a 7.8 Mb linear chromosome with 71.5% GC content. AntiSMASH analysis indicated at least thirty one distinct secondary metabolite gene clusters were encoded in its genome with only one type II polyketide synthetic gene cluster, whose gene products show high similarity to proteins involved in other angucycline biosynthesis [2]. The putative may gene cluster spans a 23.2 kb contiguous DNA region consisting of 20 genes responsible for biosynthesis, regulation, and transporter. The nucleotide sequence have been deposited in the Genbank under accession number MG601230.
Functional assignments for the gene products within may gene cluster were made by sequence analysis through BLAST comparison. Biosynthesis of angucycline aglycone was initiated by the minimal type II PKS cassette, May16 (KSα), May15 (KSβ), and May14 (ACP) which utilize one acetyl CoA and nine malonyl-CoA to form a linear polyketide backbone. May12, May13, and May17 are homologues to bifunctional cyclase/dehydrase JadD, ketoreductase JadE, and polyketide cyclase JadI, respectively, in jadomycin biosynthesis. It is thus anticipated that the products of may12, may13, and may17 are sufficient for the formation of tetracyclic ring [12,13,14,15]. The subsequent two steps of dehydration followed by oxidation led to the formation of desired aglycone (Fig. 3).
Six genes including may5, may6, may7, may9, may10, and may22 encode proteins similar to Med-ORF16, Med-ORF15, Med-ORF20, Med-ORF17, Med-ORF18, Med-ORF14, which are essential for the biosynthesis of aminosugar moiety of medemycin (Table 3) [16], suggesting these proteins were responsible for synthesizing aminosugar moiety in compounds 1 and 2. A C-glycosyltransferase, May21, catalyzes the final C-glycosylation step using either 3 or 4 as aminosugar donors to finally form 1 and 2 [16,17,18,19].
In summary, a new type II polyketide, mayamycin B (1), together with its known congener mayamycin (2) were isolated and characterized from Streptomyces sp. 120454. Compound 1 showed potent antibacterial bioactivity against Micrococcus luteus. Sequencing and bioinformatics analysis of S. sp. 120454 allow us to propose the biosynthetic pathway of mayamycin for the first time.
Mayamycin B (1): dark brown amorphous solid; UV (MeOH) λmax (lgε) 440 (2.83), 328 (3.02), 298 (2.98), 236 (3.26); IR (KBr) νmax cm−1: 3250, 2922, 2857, 2360, 1608, 1420; 1H (600 MHz) and 13C (150 MHz) NMR data see Table 1; HRESIMS m/z: 450.1497 [M+H]+ (calcd. for C25H24NO7, 450.1508).
References
Minotti G, et al. Anthracyclines: molecular advances and pharmacologic developments in antitumor activity and cardiotoxicity. Pharmacol Rev. 2004;56:185–229.
Kharel MK, et al. Angucyclines: biosynthesis, mode-of-action, new natural products and synthesis. Nat Prod Rep. 2012;29:264–325.
Das A, Khosla C. Biosynthesis of aromatic polyketides in bacteria. Acc Chem Res. 2009;42:631–639.
Moore BS, Hertweck C. Biosynthesis and attachment of novel bacterial polyketide synthase starter units. Nat Prod Rep. 2002;19:70–99.
Omura S, et al. New antitumor antibiotics, OS-4742A1, A2, B1 and B2 produced by a strain of Streptomyces. J Antibiot. 1997;30:908–16.
Martin GDA, et al. Marmycins A and B, cytotoxic pentacyclic C-glycosides from a marine sediment-derived actinomycete related to the genus Streptomyces. J Nat Prod. 2007;70:1406–9.
Shaaban KA, et al. 11-Deoxylandomycinone and landomycins X-Z, new cytotoxic angucyclin(on)es from a Streptomyces cyanogenus K62 mutant strain. J Antibiot. 2011;64:141–50.
Patrikainen P, et al. Structure-based engineering of angucyclinone 6-ketoreductases. Chem Biol. 2014;21:1381–1391.
Zhu XC, et al. Cytotoxic rearranged angucycline glycosides from deep sea-derived Streptomyces lusitanus SCSIO LR32. J Antibiot. 2017;70:819–22.
Imke S, et al. Mayamycin, a cytotoxic polyketide from a Streptomyces strain isolated from the marine sponge Halichondria panacea. J Nat Prod. 2010;73:1309–12.
Liang. Y, et al. Bioactive polycyclic quinones from marine Streptomyces sp. 182SMLY. Mar Drugs. 2016;14:10.
Han L, et al. Cloning and characterization of polyketide synthase genes for jadomycin B biosynthesis in Streptomyces venezuelae ISP5230. Microbiology. 1994;140:3379–89.
Rix U, et al. The oxidative ring cleavage in jadomycin biosynthesis: a multistep oxygenation cascade in a biosynthetic black box. ChemBioChem. 2005;6:838–45.
Chen YH, et al. Functional analyses of oxygenases in jadomycin biosynthesis and identification of JadH as a bifunctional oxygenase/dehydrase. J Biol Chem. 2005;280:22508–14.
Kulowski K, et al. Functional characterization of the jadI gene as a cyclase forming angucyclinones. J Am Chem Soc. 1999;121:1786–94.
Ichinose K, et al. Cloning, sequencing and heterologous expression of the medermycin biosynthetic gene cluster of Streptomyces sp. AM-7161: towards comparative analysis of the benzoisochromanequinone gene clusters. Microbiology. 2003;149:1633–45.
Ichinose K, et al. The granaticin biosynthetic gene cluster of Streptomyces violaceoruber Tü22: sequence analysis and expression in a heterologous host. Chem Biol. 1998;5:647–59.
Faust B, et al. Two new tailoring enzymes, a glycosyltransferase and an oxygenase, involved in biosynthesis of the angucycline antibiotic urdamycin A in Streptomyces fradiae Tü2717. Microbiology. 2000;146:147–54.
Trefzer A, et al. Biosynthetic gene cluster of simocyclinone, a natural multihybrid antibiotic. Antimicrob Agents Chemother. 2002;46:1174–82.
Acknowledgements
We thank Dr. Ben Shen (The Scripps Research Institute) for his generous gift of S. sp. 120454. This work was financially supported by Natural Science Foundation of China (81522042, 21572100, 81421091, 81500059, 81673333, and 21672101), and Jiangsu Provincial Key Medical Discipline (laboratory) (no. ZDXKA2016020).
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Bo, S.T., Xu, Z.F., Yang, L. et al. Structure and biosynthesis of mayamycin B, a new polyketide with antibacterial activity from Streptomyces sp. 120454. J Antibiot 71, 601–605 (2018). https://doi.org/10.1038/s41429-018-0039-x
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DOI: https://doi.org/10.1038/s41429-018-0039-x
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