Browsing by Author "Fang, Q."
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Item Accramycin A, A New Aromatic Polyketide, from the Soil Bacterium, Streptomyces sp. MA37(molecules, 2019-09-12) Kyeremeh, K.; Maglangit, F.; Fang, Q.; Leman, V.; Soldatou, S.; Ebel, R.; Deng, H.Abstract: Drug-like molecules are known to contain many di erent building blocks with great potential as pharmacophores for drug discovery. The continued search for unique sca olds in our laboratory led to the isolation of a novel Ghanaian soil bacterium, Streptomyces sp. MA37. This strain produces many bioactive molecules, most of which belong to carbazoles, pyrrolizidines, and fluorinated metabolites. Further probing of the metabolites of MA37 has led to the discovery of a new naphthacene-type aromatic natural product, which wehave named accramycinA1. This molecule was isolated using an HPLC-photodiode array (PDA) guided isolation process and MS/MS molecular networking. The structure of 1 was characterized by detailed analysis of LC-MS, UV, 1D, and 2D NMR data. Preliminary studies on the antibacterial properties of 1 using Group B Streptococcus (GBS) produced a minimum inhibitory concentration (MIC) of 27 g/mL. This represents the first report of such bioactivity amongst the naphthacene-type aromatic polyketides, and also suggests the possibility for the further development of potent molecules against GBS based on the accramycin sca old. A putative acc biosynthetic pathway for accramycin, featuring a tridecaketide-specific type II polyketide synthase, was proposed.Item A Co-Culturing Approach Enables Discovery and Biosynthesis of a Bioactive Indole Alkaloid Metabolite(molecules, 2020-01-08) Kyeremeh, K.; Maglangit, F.; Fang, Q.; Sternberg, J.M.; Ebel, R.; Deng, H.Whole-genome sequence data of the genus Streptomyces have shown a far greater chemical diversity of metabolites than what have been discovered under typical laboratory fermentation conditions. In our previous natural product discovery e orts on Streptomyces sp. MA37, a bacterium isolated from the rhizosphere soil sample in Legon, Ghana, we discovered a handful of specialised metabolites from this talented strain. However, analysis of the draft genome of MA37 suggested that most of the encoded biosynthetic gene clusters (BGCs) remained cryptic or silent, and only a small fraction of BGCs for the production of specialised metabolites were expressed when cultured in our laboratory conditions. In order to induce the expression of the seemingly silent BGCs, we have carried out a co-culture experiment by growing the MA37 strain with the Gram-negative bacterium Pseudomonas sp. in a co-culture chamber that allows co-fermentation of two microorganisms with no direct contact but allows exchange of nutrients, metabolites, and other chemical cues. This co-culture approach led to the upregulation of several metabolites that were not previously observed in the monocultures of each strain. Moreover, the co-culture induced the expression of the cryptic indole alkaloid BGC in MA37 and led to the characterization of the known indolocarbazole alkaloid, BE-13793C 1. Neither bacterium produced compound 1 when cultured alone. The structure of 1 was elucidated by Nuclear Magnetic Resonance (NMR), mass spectrometry analyses and comparison of experimental with literature data. A putative biosynthetic pathway of 1 was proposed. Furthermore, BE-13793C 1 showed strong anti-proliferative activity against HT-29 (ATCC HTB-38) cells but no toxic e ect to normal lung (ATCC CCL-171) cells. To the best of our knowledge, this is the first report for the activity of 1 against HT-29. No significant antimicrobial and anti-trypanosomal activities for 1 were observed. This research provides a solid foundation for the fact that a co-culture approach paves the way for increasing the chemical diversity of strain MA37. Further characterization of other upregulated metabolites in this strain is currently ongoing in our laboratory.Item Enzymatic Reconstitution and Biosynthetic Investigation of the Bacterial Carbazole Neocarazostatin A(The Journal of Organic Chemistry, 2019-11-15) Kyeremeh, K.; Liu, Y.; Su, L.; Fang, Q.; Tabudravu, J.; Yang, X.; Rickaby, K.; Trembleau, L.; Deng, Z.; Deng, H.; Yu, Y.Tricyclic carbazole is an important scaffold in many naturally occurring metabolites, as well as valuable building blocks. Here we report the reconstitution of the ring A formation of the bacterial neocarazostatin A carbazole metabolite. We provide evidence of the involvement of two unusual aromatic polyketide proteins. This finding suggests how new enzymatic activities can be recruited to specific pathways to expand biosynthetic capacities. Finally, we leveraged our bioinformatics survey to identify the untapped capacity of carbazole biosynthesisItem Genomic scanning enabling discovery of a new antibacterial bicyclic carbamate-containing alkaloid(Synthetic and Systems Biotechnology, 2021) Fang, Q.; Wu, L.; Urwald, C.; Mugat, M.; Wang, S.; Kyeremeh, K.; Philips, C.; Law, S.; Zhou, Y.; Deng, H.Non-ribosomal peptides are a group of structurally diverse natural products with various important therapeutic and agrochemical applications. Bacterial pyrrolizidine alkaloids (PAs), containing a scaffold of two fused fivemembered ring system with a nitrogen atom at the bridgehead, have been found to originate from a multidomain non-ribosomal peptide synthetase to generate indolizidine intermediates, followed by multistep oxidation, catalysed by single Bayer-Villiger (BV) enzymes, to yield PA scaffolds. Although bacterial PAs are rare in natural product inventory, bioinformatics analysis suggested that the biosynthetic gene clusters (BGCs) that are likely to be responsible for the production of PA-like metabolites are widely distributed in bacterial genomes. However, most of the strains containing PA-like BGCs are not deposited in the public domain, therefore preventing further assessment of the chemical spaces of this group of bioactive metabolites. Here, we report a genomic scanning strategy to assess the potential of PA metabolites production in our culture collection without prior knowledge of genome information. Among the strains tested, we found fifteen contain the key BV enzymes that are likely to be involved in the last step of PA ring formation. Subsequently one-strain-many-compound (OSMAC) method, supported by a combination of HR-MS, NMR, SMART 2.0 technology, and GNPS analysis, allowed identification and characterization of a new [5 + 7] heterobicyclic carbamate, legoncarbamate, together with five known PAs, bohemamine derivatives, from Streptomyces sp. CT37, a Ghanaian soil isolate. The absolute stereochemistry of legoncarbamate was determined by comparison of measured and calculated ECD spectra. Legoncarbamate displays antibacterial activity against E. coli ATCC 25922 with an MIC value of 3.1 μg/mL. Finally, a biosynthetic model of legoncarbamate and other bohemamines was proposed based on the knowledge we have gained so far.Item Signalling and Bioactive Metabolites from Streptomyces sp. RK44(Molecules, 2020-01-22) Kyeremeh, K.; Fang, Q.; Maglangit, F.; Wu, L.; Ebel, R.; Andersen, J.H.; Annang, F.; Pérez-Moreno, G.; Reyes, F.; Deng, H.Streptomyces remains one of the prolific sources of structural diversity, and a reservoir to mine for novel natural products. Continued screening for new Streptomyces strains in our laboratory led to the isolation of Streptomyces sp. RK44 from the underexplored areas of Kintampo waterfalls, Ghana, Africa. Preliminary screening of the metabolites from this strain resulted in the characterization of a new 2-alkyl-4-hydroxymethylfuran carboxamide (AHFA) 1 together with five known compounds, cyclo-(L-Pro-Gly) 2, cyclo-(L-Pro-L-Phe) 3, cyclo-(L-Pro-L-Val) 4, cyclo-(L-Leu-Hyp) 5, and deferoxamine E 6. AHFA 1, a methylenomycin (MMF) homolog, exhibited anti-proliferative activity (EC50 = 89.6 M) against melanoma A2058 cell lines. This activity, albeit weak is the first report amongst MMFs. Furthermore, the putative biosynthetic gene cluster (ahfa) was identified for the biosynthesis of AHFA 1. DFO-E 6 displayed potent anti-plasmodial activity (IC50 = 1.08 M) against P. falciparum 3D7. High-resolution electrospray ionization mass spectrometry (HR ESIMS) and molecular network assisted the targeted-isolation process, and tentatively identified six AHFA analogues, 7–12 and six siderophores 13–18.Item Targeted Isolation of Indole Alkaloids from Streptomyces sp. CT37(molecules, 2020-03-02) Kyeremeh, K.; Fang, Q.; Maglangit, F.; Mugat, M.; Urwald, C.; Deng, H.Four compounds (1–4) were isolated from the extracts of Streptomyces sp. CT37 using bioassay in conjunction with mass spectrometric molecular networking (MN) driven isolation. Their complete structures were established by high-resolution electrospray ionization mass spectrometry (HR-ESIMS), and 1D and 2D nuclear magnetic resonance (NMR) data. Legonimide 1 was identified as a new alkaloid containing a rare linear imide motif in its structure, while compounds 2–4 were already known and their structures were elucidated as 1H-indole-3-carbaldehyde, actinopolymorphol B, (2R,3R)-1-phenylbutane-2,3-diol, respectively. The biosynthetic pathways of 1–4 were proposed based on the reported biogenesis of indole alkaloids in literature. Bioactivity tests for 1 and 2 revealed moderate growth inhibition activity against Candida albicans ATCC 10231 with MIC95 values of 21.54 g/mL and 11.47 g/mL, respectively.Item An unusual metal-bound 4-fluorothreonine transaldolase from Streptomyces sp. MA37 catalyses promiscuous transaldol reactions(Applied Microbiology and Biotechnology, 2020-03-06) Kyeremeh, K.; Wu, L.; Tong, M.H.; Raab, A.; Fang, Q.; Wang, S.; Yu, Y.; Deng, H.β-Hydroxy-α-amino acids (βH-AAs) are key components of many bioactive molecules as well as exist as specialised metabolites. Among these βH-AAs, 4-fluorothreonine (4-FT) is the only naturally occurring fluorinated AA discovered thus far. Here we report overexpression and biochemical characterisation of 4-fluorothreonine transaldolase from Streptomyces sp. MA37 (FTaseMA), a homologue of FTase previously identified in the biosynthesis of 4-FT in S. cattleya. FTaseMA displays considerable substrate plasticity to generate 4-FT as well as other β-hydroxy-α-amino acids with various functionalities at C4 position, giving the prospect of new chemo-enzymatic applications. The enzyme has a hybrid of two catalytic domains, serine hydroxymethyltransferase (S) and aldolase (A). Site-directed mutagenesis allowed the identification of the key residues of FTases, suggesting that the active site of A domain has a historical reminiscent feature in metal-dependent aldolases. Elemental analysis demonstrated that FTaseMA is indeed a Zn2+-dependent enzyme, the first example of pyridoxal phosphate (PLP) enzyme family fused with a metal-binding domain carrying out a distinct catalytic role. Finally, FTaseMA showed divergent evolutionary origin with other PLP dependent enzymes