Biosynthesis of the Fusarium Mycotoxin (-)-Sambutoxin

Comprehensive microcrystal electron diffraction sample preparation for cryo-EM

Microcrystal electron diffraction (MicroED) has advanced structural methods across a range of sample types, from small molecules to proteins. This cryogenic electron microscopy (cryo-EM) technique involves the continuous rotation of small 3D crystals in the electron beam, while a high-speed camera captures diffraction data in the form of a movie. The crystal structure is subsequently determined by using established X-ray crystallographic software. MicroED is a technique still under development, and hands-on expertise in sample preparation, data acquisition and processing is not always readily accessible. This comprehensive guide on MicroED sample preparation addresses commonly used methods for various sample categories, including room temperature solid-state small molecules and soluble and membrane protein crystals. Beyond detailing the steps of sample preparation for new users, and because every crystal requires unique growth and sample-preparation conditions, this resource provides instructions and optimization strategies for MicroED sample preparation. The protocol is suitable for users with expertise in biochemistry, crystallography, general cryo-EM and crystallography data processing. MicroED experiments, from sample vitrification to final structure, can take anywhere from one workday to multiple weeks, especially when cryogenic focused ion beam milling is involved.

Arcopilins: A New Family of Staphylococcus aureus Biofilm Disruptors from the Soil Fungus Arcopilus navicularis

Biofilms represent a key challenge in the treatment of microbial infections; for instance, Staphylococcus aureus causes chronic or fatal infections by forming biofilms on medical devices. Herein, the fungus Arcopilus navicularis was found to produce a novel family of PKS-NRPS metabolites that are able to disrupt preformed biofilms of S. aureus. Arcopilins A-F (1-6), tetramic acids, and arcopilin G (7), a 2-pyridone, were elucidated using HR-ESI-MS and one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy. Their absolute configuration was established by the synthesis of MPTA-esters for 2, analysis of 1H-1H coupling constants, and ROESY correlations, along with comparison with the crystal structure of 7. Arcopilin A (1) not only effectively disrupts preformed biofilms of S. aureus but also potentiates the activity of gentamicin and vancomycin up to 115- and 31-fold times, respectively. Our findings demonstrate the potential application of arcopilins for the conjugated treatment of infections caused by S. aureus with antibiotics unable to disrupt preformed biofilms.

The chemical structures, biosynthesis, and biological activities of secondary metabolites from the culinary-medicinal mushrooms of the genus Hericium: a review

Fungal phytochemicals derived from higher fungi, particularly those from the culinary-medicinal genus Hericium, have gained significant attention in drug discovery and healthcare. This review aims to provide a comprehensive analysis of the chemical structures, biosynthetic pathways, biological activities, and pharmacological properties of monomeric compounds isolated from Hericium species. Over the past 34 years, 253 metabolites have been identified from various Hericium species, including cyathane diterpenes, alkaloids, benzofurans, chromenes, phenols, pyrones, steroids, and other miscellaneous compounds. Detailed investigations into the biosynthesis of erinacines, a type of cyathane diterpene, have led to the discovery of novel cyathane diterpenes. Extensive research has highlighted the biological activities and pharmacological properties of Hericium-derived compounds, with particular emphasis on their neuroprotective and neurotrophic effects, immunomodulatory capabilities, anti-cancer activity, antioxidant properties, and antimicrobial actions. Erinacine A, in particular, has been extensively studied. Genomic, transcriptomic, and proteomic analyses of Hericium species have facilitated the discovery of new compounds and provided insights into enzymatic reactions through genome mining. The diverse chemical structures and biological activities of Hericium compounds underpin their potential applications in medicine and as dietary supplements. This review not only advances our understanding of Hericium compounds but also encourages further research into Hericium species within the realms of medicine, health, functional foods, and agricultural microbiology. The broad spectrum of compound types and their diverse biological activities present promising opportunities for the development of new pharmaceuticals and edible products.

Total Synthesis of Fusaramin, Enabling Stereochemical Elucidation, Structure-Activity Relationship, and Uncovering the Hidden Antimicrobial Activity against Plant Pathogenic Fungi

Fusaramin (1) was isolated as a mitochondrial inhibitor. However, the fungal producer stops producing 1, which necessitates us to supply 1 by total synthesis. We proposed the complete stereochemical structure based on the biosynthetic pathway of sambutoxin. We have established concise and robust total synthesis of 1, enabling us to determine the complete stereochemical structure and to elucidate the structure-activity relationship, and uncover the hidden antiplant pathogenic fungal activity.

Bioinformatic Analysis of Secondary Metabolite Biosynthetic Potential in Pathogenic Fusarium

Fusarium species are among the filamentous fungi with the most pronounced impact on agricultural production and human health. The mycotoxins produced by pathogenic Fusarium not only attack various plants including crops, causing various plant diseases that lead to reduced yields and even death, but also penetrate into the food chain of humans and animals to cause food poisoning and consequent health hazards. Although sporadic studies have revealed some of the biosynthetic pathways of Fusarium toxins, they are insufficient to satisfy the need for a comprehensive understanding of Fusarium toxin production. In this study, we focused on 35 serious pathogenic Fusarium species with available genomes and systematically analyzed the ubiquity of the distribution of identified Fusarium- and non-Fusarium-derived fungal toxin biosynthesis gene clusters (BGCs) in these species through the mining of core genes and the comparative analysis of corresponding BGCs. Additionally, novel sesterterpene synthases and PKS_NRPS clusters were discovered and analyzed. This work is the first to systematically analyze the distribution of related mycotoxin biosynthesis in pathogenic Fusarium species. These findings enhance the knowledge of mycotoxin production and provide a theoretical grounding for the prevention of fungal toxin production using biotechnological approaches.

Elucidation of a Dearomatization Route in the Biosynthesis of Oxysporidinone Involving a TenA-like Cytochrome P450 Enzyme

Oxidative dearomatization of phenols is an important transformation for synthesis of complex molecules. Oxysporidinone and related 2-pyridones feature a hydroxy-substituted cyclohexanone ring, which has been proposed to form by phenol dearomatization, although the details of the biochemical process are still unknown. In this study, we identified the oxysporidinone biosynthetic gene cluster in Fusarium oxysporum by regulator activation and gene knockout studies. Through in vivo and in vitro studies, we confirmed that the phenol dearomatization process involves two enzymes. OsdM, a TenA-like cytochrome P450 with expected ring-expansion activity, converts the phenol ring and the 4-hydroxy-2-pyridone core into an unexpected fused [6-5-6] ring system. OsdN, on the other hand, catalyzes two successive ene reduction reactions, followed by hydroxylation by OsdM. This new route enriches current knowledge on enzymatic phenol dearomatization and the mechanism of TenA-like P450s.

Biosynthesis of AS2077715 and Funiculosin: Pathway Reconstitution and Identification of Enzymes that Form the All-cis Cyclopentanetetraol Moiety

The complete biosynthetic pathways of the potent antifungals AS2077715 (1) and funiculosin (2) are reconstituted and characterized. A five-enzyme cascade, including a multifunctional flavin-dependent monooxygenease and a repurposed O-methyltransferase, is involved to perform the dearomatization, stereoselective ring contraction, and redox transformations to morph a hydroxyphenyl-containing precursor into the unusual all-cis cyclopentanetetraol moiety.

Deciphering chemical logic of fungal natural product biosynthesis through heterologous expression and genome mining

Covering: 2010 to 2022Heterologous expression of natural product biosynthetic gene clusters (BGCs) has become a widely used tool for genome mining of cryptic pathways, bottom-up investigation of biosynthetic enzymes, and engineered biosynthesis of new natural product variants. In the field of fungal natural products, heterologous expression of a complete pathway was first demonstrated in the biosynthesis of tenellin in Aspergillus oryzae in 2010. Since then, advances in genome sequencing, DNA synthesis, synthetic biology, etc. have led to mining, assignment, and characterization of many fungal BGCs using various heterologous hosts. In this review, we will highlight key examples in the last decade in integrating heterologous expression into genome mining and biosynthetic investigations. The review will cover the choice of heterologous hosts, prioritization of BGCs for structural novelty, and how shunt products from heterologous expression can reveal important insights into the chemical logic of biosynthesis. The review is not meant to be exhaustive but is rather a collection of examples from researchers in the field, including ours, that demonstrates the usefulness and pitfalls of heterologous biosynthesis in fungal natural product discovery.

Recent Advances in Biocatalysis for Drug Synthesis

Biocatalysis is constantly providing novel options for the synthesis of active pharmaceutical ingredients (APIs). In addition to drug development and manufacturing, biocatalysis also plays a role in drug discovery and can support many active ingredient syntheses at an early stage to build up entire scaffolds in a targeted and preparative manner. Recent progress in recruiting new enzymes by genome mining and screening or adapting their substrate, as well as product scope, by protein engineering has made biocatalysts a competitive tool applied in academic and industrial spheres. This is especially true for the advances in the field of nonribosomal peptide synthesis and enzyme cascades that are expanding the capabilities for the discovery and synthesis of new bioactive compounds via biotransformation. Here we highlight some of the most recent developments to add to the portfolio of biocatalysis with special relevance for the synthesis and late-stage functionalization of APIs, in order to bypass pure chemical processes.

Michael Addition of 3-Oxo-3-phenylpropanenitrile to Linear Conjugated Enynones: Approach to Polyfunctional δ-Diketones as Precursors for Heterocycle Synthesis

Reaction of linear conjugated enynones, 1,5-diarylpent-2-en-4-yn-1-ones [Ar¹C≡CCH=CHC(=O)Ar²], with 3-oxo-3-phenylpropanenitrile (NCCH₂COPh) in the presence of sodium methoxide MeONa as a base in MeOH at room temperature for 4–26 h affords polyfunctional δ-diketones as a product of regioselective Michael addition to the double carbon–carbon bond of starting enynones. The δ-diketones have been formed as mixtures of two diastereomers in a ratio of 2.5:1 in good general yields of 53–98%. A synthetic potential of the obtained δ-diketones has been demonstrated by heterocyclization with hydrazine into substututed 5,6-dihydro-4H-1,2-diazepine.

Biosynthesis of Calipyridone A Represents a Fungal 2-Pyridone Formation without Ring Expansion in Aspergillus californicus

A chemical investigation of the filamentous fungus Aspergillus californicus led to the isolation of a polyketide-nonribosomal peptide hybrid, calipyridone A (1). A putative biosynthetic gene cluster cpd for production of 1 was next identified by genome mining. The role of the cpd cluster in the production of 1 was confirmed by multiple gene deletion experiments in the host strain as well as by heterologous expression of the hybrid gene cpdA inAspergillus oryzae. Moreover, chemical analyses of the mutant strains allowed the biosynthesis of 1 to be elucidated. The results indicate that the generation of the 2-pyridone moiety of 1 via nucleophilic attack of the iminol nitrogen to the carbonyl carbon is different from the biosynthesis of other fungal 2-pyridone products through P450-catalyzed tetramic acid ring expansions. In addition, two biogenetic intermediates, calipyridones B and C, showed modest inhibition effects on the plaque-forming ability of SARS-CoV-2.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as asporychalasin from Aspergillus oryzae.