SorF: a glycosyltransferase with promiscuous donor substrate specificity in vitro

Expanding the Ajudazol Cytotoxin Scaffold: Insights from Genome Mining, Biosynthetic Investigations, and Novel Derivatives

Myxobacteria have proven to be a rich source of natural products, but their biosynthetic potential seems to be underexplored given the high number of biosynthetic gene clusters present in their genomes. In this study, a truncated ajudazol biosynthetic gene cluster in Cystobacter sp. SBCb004 was identified using mutagenesis and metabolomics analyses and a set of novel ajudazols (named ajudazols C-J, 3-10, respectively) were detected and subsequently isolated. Their structures were elucidated using comprehensive HR-MS and NMR spectroscopy. Unlike the known ajudazols A (1) and B (2), which utilize acetyl-CoA as the biosynthetic starter unit, these novel ajudazols were proposed to incorporate 3,3-dimethylacrylyl CoA as the starter. Ajudazols C-J (3-10, respectively) are characterized by varying degrees of hydroxylation, desaturation, and different glycosylation patterns. Two P450-dependent enzymes and one glycosyltransferase are shown to be responsible for the hydroxylation at C-8, the desaturation at C-15 and C-33, and the transfer of a d-β-glucopyranose, respectively, based on mutagenesis results. One of the cytochrome P450-dependent enzymes and the glycosyltransferase were found to be encoded by genes located outside the biosynthetic gene cluster. Ajudazols C-H (3-8, respectively) exhibit cytotoxicity against various cancer cell lines.

Beyond the approved: target sites and inhibitors of bacterial RNA polymerase from bacteria and fungi

Covering: 2016 to 2022RNA polymerase (RNAP) is the central enzyme in bacterial gene expression representing an attractive and validated target for antibiotics. Two well-known and clinically approved classes of natural product RNAP inhibitors are the rifamycins and the fidaxomycins. Rifampicin (Rif), a semi-synthetic derivative of rifamycin, plays a crucial role as a first line antibiotic in the treatment of tuberculosis and a broad range of bacterial infections. However, more and more pathogens such as Mycobacterium tuberculosis develop resistance, not only against Rif and other RNAP inhibitors. To overcome this problem, novel RNAP inhibitors exhibiting different target sites are urgently needed. This review includes recent developments published between 2016 and today. Particular focus is placed on novel findings concerning already known bacterial RNAP inhibitors, the characterization and development of new compounds isolated from bacteria and fungi, and providing brief insights into promising new synthetic compounds.

GDP-Mannose 3,5-Epimerase: A View on Structure, Mechanism, and Industrial Potential

GDP-mannose 3,5-epimerase (GM35E, GME) belongs to the short-chain dehydrogenase/reductase (SDR) protein superfamily and catalyses the conversion of GDP-d-mannose towards GDP-l-galactose. Although the overall reaction seems relatively simple (a double epimerization), the enzyme needs to orchestrate a complex set of chemical reactions, with no less than 6 catalysis steps (oxidation, 2x deprotonation, 2x protonation and reduction), to perform the double epimerization of GDP-mannose to GDP-l-galactose. The enzyme is involved in the biosynthesis of vitamin C in plants and lipopolysaccharide synthesis in bacteria. In this review, we provide a clear overview of these interesting epimerases, including the latest findings such as the recently characterized bacterial and thermostable GM35E representative and its mechanism revision but also focus on their industrial potential in rare sugar synthesis and glycorandomization.

Flavonoids, terpenoids, and polyketide antibiotics: Role of glycosylation and biocatalytic tactics in engineering glycosylation

Flavonoids, terpenoids, and polyketides are structurally diverse secondary metabolites used widely as pharmaceuticals and nutraceuticals. Most of these molecules exist in nature as glycosides, in which sugar residues act as a decisive factor in their architectural complexity and bioactivity. Engineering glycosylation through selective trimming or extension of the sugar residues in these molecules is a prerequisite to their commercial production as well to creating novel derivatives with specialized functions. Traditional chemical glycosylation methods are tedious and can offer only limited end-product diversity. New in vitro and in vivo biocatalytic tools have emerged as outstanding platforms for engineering glycosylation in these three classes of secondary metabolites to create a large repertoire of versatile glycoprofiles. As knowledge has increased about secondary metabolite-associated promiscuous glycosyltransferases and sugar biosynthetic machinery, along with phenomenal progress in combinatorial biosynthesis, reliable industrial production of unnatural secondary metabolites has gained momentum in recent years. This review highlights the significant role of sugar residues in naturally occurring flavonoids, terpenoids, and polyketide antibiotics. General biocatalytic tools used to alter the identity and pattern of sugar molecules are described, followed by a detailed illustration of diverse strategies used in the past decade to engineer glycosylation of these valuable metabolites, exemplified with commercialized products and patents. By addressing the challenges involved in current bio catalytic methods and considering the perspectives portrayed in this review, exceptional drugs, flavors, and aromas from these small molecules could come to dominate the natural-product industry.

Glycosyltransferases: mechanisms and applications in natural product development

Glycosylation reactions mainly catalyzed by glycosyltransferases (Gts) occur almost everywhere in the biosphere, and always play crucial roles in vital processes.

Antibiotics from myxobacteria

Covering: up to the end of 2013. Myxobacteria produce a vast range of structurally diverse natural products with prominent biological activities. Here, we provide a detailed description and judge the potential of all antibiotically active myxobacterial compounds as lead structures, pointing out their particularities and, if known, their mode of action. Thus, the review provides an overview of the potential of specific compounds, suitable for future investigations and possible clinical applications.

Natural-product sugar biosynthesis and enzymatic glycodiversification

Many biologically active small-molecule natural products produced by microorganisms derive their activities from sugar substituents. Changing the structures of these sugars can have a profound impact on the biological properties of the parent compounds. This realization has inspired attempts to derivatize the sugar moieties of these natural products through exploitation of the sugar biosynthetic machinery. This approach requires an understanding of the biosynthetic pathway of each target sugar and detailed mechanistic knowledge of the key enzymes. Scientists have begun to unravel the biosynthetic logic behind the assembly of many glycosylated natural products and have found that a core set of enzyme activities is mixed and matched to synthesize the diverse sugar structures observed in nature. Remarkably, many of these sugar biosynthetic enzymes and glycosyltransferases also exhibit relaxed substrate specificity. The promiscuity of these enzymes has prompted efforts to modify the sugar structures and alter the glycosylation patterns of natural products through metabolic pathway engineering and enzymatic glycodiversification. In applied biomedical research, these studies will enable the development of new glycosylation tools and generate novel glycoforms of secondary metabolites with useful biological activity.