Biosynthesis of the Thiofuranose Core in Albomycin Requires a Versatile Enzyme AbmG That Catalyzes Net Dehydration via Cryptic Phosphorylation.

Albomycins are unusual sulfur-containing nucleosides from the species of that exhibit potent antibiotic activities against both Gram-negative and Gram-positive bacteria including clinical pathogens. Previous studies demonstrated that the twitch radical SAM enzyme AbmM catalyzes an oxidative sulfur-for-oxygen swapping reaction converting CDP to a 4'-hydroxy-4'-thiocytidine 5'-diphosphate intermediate in the initial step of albomycin biosynthesis. However, the fate of this intermediate in the biosynthetic pathway has remained elusive.

Radical Propagation via σ-Cleavage Mediates Radical SAM Catalyzed Sulfur-for-Oxygen Swapping Reaction during the Biosynthesis of Albomycin δ.

AbmM is a radical -adenosyl l-methionine (SAM) enzyme that catalyzes a radical initiated sulfur-for-oxygen swapping reaction, transforming the furanose ring of cytidine diphosphate (CDP) to a 4'-hydroxy-4'-thiofuranose product. While the function of AbmM has been demonstrated, the underlying mechanism regarding the formation of the radical intermediates during the reaction pathway remains to be fully established. To gain additional insight into this vital step in the biosynthesis of albomycin δ, 2'-deoxy-2'-methylidene CDP was synthesized as a mechanistic probe.

Radical -adenosyl-l-methionine FeS cluster implicated as the sulfur donor during albomycin biosynthesis.

Carbon-sulfur bond-forming reactions in natural product biosynthesis largely involve Lewis acid/base chemistry with relatively few examples catalysed by radical -adenosyl-l-methionine (SAM) enzymes. The latter have been limited to radical-mediated sulfur insertion into carbon-hydrogen bonds with the sulfur atom originating from a sacrificial auxiliary iron-sulfur cluster. Here we show that the radical SAM enzyme AbmM encoded in the albomycin biosynthetic gene cluster catalyses a sulfur-for-oxygen swapping reaction, transforming the furanose ring of cytidine 5'-diphosphate to a thiofuranose moiety that is essential for the antibacterial activity of albomycin δ.

Biosynthesis of guanidine-containing natural products in cyanobacteria.

Cyanobacteria are prolific producers of structurally diverse and biologically potent natural products, a subset of which feature guanidino moieties. Introduction and modification of the guanidine group confer tuned basicity and enable extensive hydrogen bonding, cation-π, and electrostatic interactions, facilitating high-affinity binding to numerous biological targets. Although the enzymatic processes responsible for guanidine modifications in cyanobacterial pathways remain somewhat obscure, recent investigations have begun to clarify the biosynthetic machinery that mediates these distinctive transformations.

Nitrogen-centered radicals driving unusual enzyme reactions in biosynthetic pathways.

Nitrogen-centered radicals have emerged as versatile intermediates in natural product biosynthesis, playing pivotal roles in complex bond-forming and rearrangement reactions-including fragmentations, cyclizations, and dimerizations. These transformations enable the efficient construction of structurally intricate alkaloids, amino acids, cofactors, and other scaffolds that are often inaccessible classical polar mechanisms. This review provides an overview of the enzymatic systems discovered and characterized over the past decade that harness nitrogen-centered radicals to mediate diverse biological transformations.

Pyrroline Ring Assembly via N-Prenylation and Oxidative Carbocyclization during Biosynthesis of Aeruginosin Derivatives.

Aeruginosins are linear peptide natural products isolated from cyanobacteria and contain various arginine derivatives at their termini. 1-Amino-2-(-amidino-3-Δ3-pyrrolinyl)ethane (Aeap) is a structurally unique arginine derivative, as it has an unusual pyrroline ring with two additional carbon atoms of unknown biosynthetic origin. Here, we demonstrate that Aer3, a member of a newly identified subfamily of prenyltransferases, catalyzes selective isopentenylation of the internal N atom of agmatine.

Comparison of a Nonheme Iron Cyclopropanase with a Homologous Hydroxylase Reveals Mechanistic Features Associated with Distinct Reaction Outcomes.

Despite the diversity of reactions catalyzed by mononuclear iron and 2-oxoglutarate-dependent enzymes, the factors that lead to diverse reaction outcomes beyond canonical hydroxylation remain elusive. Cyclopropanation reactions are of particular interest not only due to the prevalence of cyclopropane moieties in pharmaceuticals but also due to the chemistry that allows cyclopropanation to outcompete oxygen rebound. HrmJ is one such cyclopropanase from the biosynthetic pathway of hormaomycin; however, a homologue is herein discovered that instead catalyzes -hydroxylation of the same nitro enolate substrate.

Structure-function analysis of 2-sulfamoylacetic acid synthase in altemicidin biosynthesis.

Altemicidin and its analogs are valuable sulfonamide antibiotics with valuable antitumor and antibacterial activities. Structures of altemicidin and congeners feature an unusual sulfonamide side chain. In the biosynthesis of altemicidin, the aldehyde dehydrogenase SbzJ catalyzes the conversion of 2-sulfamoylacetic aldehyde into 2-sulfamoylacetic acid, a key step in producing the sulfonamide side chain.

Functions and mechanisms of enzymes assembling lignans and norlignans.

Lignans and norlignans are distributed throughout the plant kingdom and exhibit diverse chemical structures and biological properties that offer potential for therapeutic use. Originating from the phenylpropanoid biosynthesis pathway, their characteristic carbon architectures are formed through unique enzyme catalysis, featuring regio- and stereoselective C-C bond forming processes. Despite extensive research on these plant natural products, their biosynthetic pathways, and enzyme mechanisms remain enigmatic.

Unusual Enzymatic C-C Bond Formation and Cleavage Reactions during Natural Product Biosynthesis.

Natural products from plants and microorganisms provide a valuable reservoir of pharmaceutical compounds. C-C bond formation and cleavage are crucial events during natural product biosynthesis, playing pivotal roles in generating diverse and intricate chemical structures that are essential for biological functions. This review summarizes our recent findings regarding biosynthetic enzymes that catalyze unconventional C-C bond formation and cleavage reactions during natural product biosynthesis.

Characterization of Aziridine-Forming α-Ketoglutarate-Dependent Oxygenase in l-Isovaline Biosynthesis.

l-Isovaline biosynthesis by TqaLFM- from was demonstrated . The biochemical analysis of the α-ketoglutarate-dependent oxygenase TqaL- revealed that it produces (2,3)-3-ethyl-3-methylaziridine-2-carboxylic acid from l-isoleucine, thus exhibiting a stereoselectivity different from those of the reported homologues. Remarkably, a single mutation on I295 in TqaL- completely exchanged its stereoselectivity to produce the C-3 stereoisomer.

Three-membered ring formation catalyzed by α-ketoglutarate-dependent nonheme iron enzymes.

Epoxides, aziridines, and cyclopropanes are found in various medicinal natural products, including polyketides, terpenes, peptides, and alkaloids. Many classes of biosynthetic enzymes are involved in constructing these ring structures during their biosynthesis. This review summarizes our current knowledge regarding how α-ketoglutarate-dependent nonheme iron enzymes catalyze the formation of epoxides, aziridines, and cyclopropanes in nature, with a focus on enzyme mechanisms.

Mechanistic Analysis of Stereodivergent Nitroalkane Cyclopropanation Catalyzed by Nonheme Iron Enzymes.

BelL and HrmJ are α-ketoglutarate-dependent nonheme iron enzymes that catalyze the oxidative cyclization of 6-nitronorleucine, resulting in the formation of two diastereomeric 3-(2-nitrocyclopropyl)alanine (Ncpa) products containing -cyclopropane rings with (1'2') and (1'2') configurations, respectively. Herein, we investigate the catalytic mechanism and stereodivergency of the cyclopropanases. The results suggest that the nitroalkane moiety of the substrate is first deprotonated to produce the nitronate form.

Diverse enzymatic chemistry for propionate side chain cleavages in tetrapyrrole biosynthesis.

Unlabelled: Tetrapyrroles represent a unique class of natural products that possess diverse chemical architectures and exhibit a broad range of biological functions. Accordingly, they attract keen attention from the natural product community. Many metal-chelating tetrapyrroles serve as enzyme cofactors essential for life, while certain organisms produce metal-free porphyrin metabolites with biological activities potentially beneficial for the producing organisms and for human use.

Photoinduced Reductive Dehalogenation of Phenacyl Bromides with Pyridoxal 5'-Phosphate.

We describe the photoinduced reductive debromination of phenacyl bromides using pyridoxal 5'-phosphate (PLP). The reaction requires irradiation with cyan or blue light in an anaerobic atmosphere. Mechanistic analysis reveals the formation of the phenacyl radical as an intermediate in the reaction, implying a single electron transfer to phenacyl bromides from a PLP-derived species resulting from excitation by illumination.

Multiple C-C Bond Cleavage Reactions Catalyzed by Tolyporphin Tetrapyrrole Biosynthetic Enzymes.

Tolyporphin A is an unusual tetrapyrrole secondary metabolite containing pendant deoxysugars and unsubstituted pyrrole β sites. Herein, we describe the biosynthesis of the tolyporphin aglycon core. HemF1 catalyzes the oxidative decarboxylation of two propionate side chains of coproporphyrinogen III, an intermediate in heme biosynthesis.

Stereoselectivity and Substrate Specificity of the Fe(II)/α-Ketoglutarate-Dependent Oxygenase TqaL.

Non-heme iron enzymes are versatile catalysts in the biosynthesis of medicinal natural products and have attracted increasing attention as practical catalytic tools in chemical synthesis due to their ability to perform chemically challenging transformations. The Fe(II)/α-ketoglutarate-dependent oxygenase TqaL catalyzes unusual aziridine formation from l-Val via cleavage of the unactivated C-H bond. However, the mechanistic details as well as the synthetic potential of TqaL-catalyzed ring closure remain unclear.

Cordycicadins A-D, Antifeedant Polyketides from the Entomopathogenic Fungus JXCH1.

Cordycicadins A-D (-) are four novel polyketides that were isolated from the liquid fermentation of the insect-pathogenic fungus JXCH1. The structures were determined by a combination of spectroscopic analysis, single-crystal X-ray diffraction, and computational methods. Compounds , , and harbor an unusual exocyclic enol ether bridge that connects the separated ring systems.

Structure-based engineering of α-ketoglutarate dependent oxygenases in fungal meroterpenoid biosynthesis.

Non-heme iron- and α-ketoglutarate-dependent oxygenases (αKG OXs) are key enzymes that play a major role in diversifying the structure of fungal meroterpenoids. They activate a specific C-H bond of the substrate to first generate radical species, which is usually followed by oxygen rebound to produce cannonical hydroxylated products. However, in some cases remarkable chemistry induces dramatic structural changes in the molecular scaffolds, depending on the stereoelectronic characters of the substrate/intermediates and the resulting conformational changes/movements of the active site of the enzyme.

Characterization of Enzymes Catalyzing the Initial Steps of the β-Lactam Tabtoxin Biosynthesis.

Tabtoxin is a β-lactam ring-containing phytotoxin produced by a plant pathogenic species. Here, we describe the early stages of tabtoxin biosynthesis, involving a -methylation reaction catalyzed by the -adenosyl-l-methionine-dependent methyltransferase TblA as the initial step for the β-lactam construction. Gene deletion and biochemical assays demonstrated that the Gcn5-related -acetyltransferase domain of TblD catalyzes the acetylation of the α-amino group of 5-methyl-l-lysine.

Stereodivergent Nitrocyclopropane Formation during Biosynthesis of Belactosins and Hormaomycins.

Belactosins and hormaomycins are peptide natural products containing 3-(2-aminocyclopropyl)alanine and 3-(2-nitrocyclopropyl)alanine residues, respectively, with opposite stereoconfigurations of the cyclopropane ring. Herein we demonstrate that the heme oxygenase-like enzymes BelK and HrmI catalyze the N-oxygenation of l-lysine to generate 6-nitronorleucine. The nonheme iron enzymes BelL and HrmJ then cyclize the nitroalkane moiety to the nitrocyclopropane ring with the desired stereochemistry found in the corresponding natural products.