Characterization of the sugar-O-methyltransferase LobS1 in lobophorin biosynthesis

Naturally Occurring and Widespread Resistance to Bioactive Natural Products

Naturally occurring resistances diminish the effectiveness of antibiotics, and present significant challenges to human health. Human activities are usually considered as the main drivers of the dissemination of antibiotic resistance, however, the origin of the clinical antibiotic resistance can be traced to the environmental microbes, and the clinically relevant resistance determinants have already pre-existed in nature before the antibiotics come into clinic. In this concept, we present the naturally occurring and widespread resistance determinants recently discovered during the biosynthesis study of bioactive compounds. These widely prevalent resistances in environmental microbes, including antibiotic producers and non-producers, advance the understanding of the origin of resistance, and provide prediction for the clinically relevant resistance to aid in the rational design of more effective drug analogues to combat resistance.

The Rare Actinobacterium Crossiella sp. Is a Potential Source of New Bioactive Compounds with Activity against Bacteria and Fungi

Antimicrobial resistance has become a global problem in recent decades. A gradual reduction in drug discoveries has led to the current antimicrobial resistance crisis. Caves and other subsurface environments are underexplored thus far, and they represent indispensable ecological niches that could offer new molecules of interest to medicine and biotechnology. We explored Spanish show caves to test the bioactivity of the bacteria dwelling in the walls and ceilings, as well as airborne bacteria. We reported the isolation of two strains of the genus Crossiella, likely representing a new species, isolated from Altamira Cave, Spain. In vitro and in silico analyses showed the inhibition of pathogenic Gram-positive and Gram-negative bacteria, and fungi, as well as the taxonomical distance of both strains from their closest relative, Crossiella cryophila. The presence of an exclusive combination of gene clusters involved in the synthesis of lanthipeptides, lasso peptides, nonribosomal peptides and polyketides indicates that species of this genus could represent a source of new compounds. Overall, there is promising evidence for antimicrobial discovery in subterranean environments, which increases the possibility of identifying new bioactive molecules.

Streptomyces sp. VN1, a producer of diverse metabolites including non-natural furan-type anticancer compound

Streptomyces sp. VN1 was isolated from the coastal region of Phu Yen Province (central Viet Nam). Morphological, physiological, and whole genome phylogenetic analyses suggested that strain Streptomyces sp. VN1 belonged to genus Streptomyces. Whole genome sequencing analysis showed its genome was 8,341,703 base pairs in length with GC content of 72.5%. Diverse metabolites, including cinnamamide, spirotetronate antibiotic lobophorin A, diketopiperazines cyclo-L-proline-L-tyrosine, and a unique furan-type compound were isolated from Streptomyces sp. VN1. Structures of these compounds were studied by HR-Q-TOF ESI/MS/MS and 2D NMR analyses. Bioassay-guided purification yielded a furan-type compound which exhibited in vitro anticancer activity against AGS, HCT116, A375M, U87MG, and A549 cell lines with IC50 values of 40.5, 123.7, 84.67, 50, and 58.64 µM, respectively. In silico genome analysis of the isolated Streptomyces sp. VN1 contained 34 gene clusters responsible for the biosynthesis of known and/or novel secondary metabolites, including different types of terpene, T1PKS, T2PKS, T3PKS, NRPS, and hybrid PKS-NRPS. Genome mining with HR-Q-TOF ESI/MS/MS analysis of the crude extract confirmed the biosynthesis of lobophorin analogs. This study indicates that Streptomyces sp. VN1 is a promising strain for biosynthesis of novel natural products.

Cytochrome P450 oxidase SlgO1 catalyzes the biotransformation of tirandamycin C to a new tirandamycin derivative

In the present study, an Escherichia coli whole cell system with overexpression of a cytochrome P450 oxidase SlgO1 involved in streptolydigin biosynthetic pathway, an E. coli flavodoxin NADP⁺ oxidoreductase (EcFLDR), and an E. coli flavodoxin A (EcFLDA) were constructed. Biotransformation experiments revealed that SlgO1 can convert tirandamycin C to tirandamycin F, indicating that it can introduce a hydroxyl group into the C-10 position of tirandamycin C. Subsequently, slgO1 was cloned into pSET152AKE vector under the downstream of ermE* promoter, which was, respectively, introduced into Streptomyces sp. SCSIO1666 (tirandamycin B producer), Streptomyces sp. Ju1008 (tirandamycin C producer), and Streptomyces sp. Ju1009 (tirandamycin E producer). A novel tirandamycin derivative tirandamycin L accumulated in the engineered strain Streptomyces sp. Ju1008::slgO1 was isolated and its structure was determined on the basis of nuclear magnetic resonance (NMR) and mass spectrometry. Unlike most of the identified tirandamycins, tirandamycin L possessed a rare C-11-C-12 saturated bond as well as a C-10 ketone moiety. In addition, tirandamycin L showed weaker antibacterial activity. Based on the structure of tirandamycin L, SlgO1 was proposed to be responsible for multiple modifications toward tirandamycin C, including the formation of C-10 hydroxyl and C-11-C-12 saturated bond.

Genome Mining and Activation of a Silent PKS/NRPS Gene Cluster Direct the Production of Totopotensamides

A 92 kb silent hybrid polyketide and nonribosomal peptide gene cluster in marine-derived Streptomyces pactum SCSIO 02999 was activated by genetically manipulating the regulatory genes, including the knockout of two negative regulators (totR5 and totR3) and overexpression of a positive regulator totR1, to direct the production of the known totopotensamides (TPMs) A (1) and B (3) and a novel sulfonate-containing analogue TPM C (2). Inactivation of totG led to accumulation of TPM B (3) lacking the glycosyl moiety, which indicated TotG as a dedicated glycosyltransferase in the biosynthesis of 1 and 2.

Characterization of Methyltransferase AlmCII in Chalcomycin Biosynthesis: The First TylF Family O-Methyltransferase Works on a 4'-Deoxysugar

Sugar O-methylation is a ubiquitous modification in natural products and plays diverse roles. This realization has inspired many attempts to search for novel methyltransferases. Chalcomycins are a group of 16-membered macrolides containing two methylated sugars that require three methyltransferases for their biosynthesis. Here, we identified that AlmCII, a sugar O-methyltransferase belonging to the TylF family that was previously only known to methylate sugars with a 4'-hydroxy group, can methylate a 4',6'-dideoxysugar during the biosynthesis of chalcomycins. An in vitro enzymatic assay revealed that AlmCII is divalent metal-dependent with an optimal pH of 8.0 and optimal temperature of 42 °C. Moreover, the 3'-O-demethylated chalcomycins exhibit less than 6 % of the antibacterial activity of their parent compounds. This is the first report demonstrating that a TylF family O-methyltransferase can use a 4'-deoxy sugar as a substrate and highlighting the importance of this methylation for the antibacterial activity of chalcomycins.

Natural [4 + 2]-Cyclases

[4 + 2]-Cycloadditions are increasingly being recognized in the biosynthetic pathways of many structurally complex natural products. A relatively small collection of enzymes from these pathways have been demonstrated to increase rates of cyclization and impose stereochemical constraints on the reactions. While mechanistic investigation of these enzymes is just beginning, recent studies have provided new insights with implications for understanding their biosynthetic roles, mechanisms of catalysis, and evolutionary origin.

Novel Lobophorins Inhibit Oral Cancer Cell Growth and Induce Atf4- and Chop-Dependent Cell Death in Murine Fibroblasts

As part of the International Cooperative Biodiversity Groups (ICBG) Program, we were interested in identifying biologically active unfolded protein response (UPR) inducing compounds from marine microorganisms isolated from Costa Rican biota. With this aim in mind we have now generated more than 33,000 unique prefractionated natural product extracts from marine and terrestrial organisms that have been submitted to the Center of Chemical Genomics (CCG) at the University of Michigan for high throughput screening (HTS). An effective complementary cell-based assay to identify novel modulators of UPR signaling was used for screening extracts. Active fractions were iteratively subjected to reverse-phase HPLC chromatographic analysis, and together with lobophorin A, B, E, and F (1-4), three new lobophorin congeners, designated as CR1 (5), CR2 (6), and CR3 (7) were isolated. Herein, we report that secondary assays revealed that the new lobophorins induced UPR-associated gene expression, inhibited oral squamous cell carcinoma cell growth, and led to UPR-dependent cell death in murine embryonic fibroblast (MEF) cells.

Spirotetronate polyketides as leads in drug discovery

The discovery of chlorothricin (1) defined a new family of microbial metabolites with potent antitumor antibiotic properties collectively referred to as spirotetronate polyketides. These microbial metabolites are structurally distinguished by the presence of a spirotetronate motif embedded within a macrocyclic core. Glycosylation at the periphery of this core contributes to the structural complexity and bioactivity of this motif. The spirotetronate family displays impressive chemical structures, potent bioactivities, and significant pharmacological potential. This review groups the family members based on structural and biosynthetic considerations and summarizes synthetic and biological studies that aim to elucidate their mode of action and explore their pharmacological potential.

Structure and activity of lobophorins from a turrid mollusk-associated Streptomyces sp

A novel lumun-lumun sampling methodology was used to obtain a large diversity of micromollusks, including the new species Lienardia totopotens. In turn, from L. totopotens we cultivated a Streptomyces sp. strain that contained new and known spirotetronate polyketides, lobophorins (1-5). The structures were elucidated using spectroscopy, and the compounds were evaluated for cytotoxicity to human cells and activity against Mycobacterium tuberculosis, Bacillus subtilis, Pseudomonas aeruginosa and Burkholderia cepacia. Compounds 2-5 showed varying degrees of activity against human cells, M. tuberculosis and B. subtilis in the low μM to mid nM range but were inactive against the other strains, while 1 lacking digitoxose was inactive. Very slight structural changes in 2-5 led to varying antibacterial:cytotoxicity ratios, providing a possible basis to synthesize more selective derivatives.