Emulating nonribosomal peptides with ribosomal biosynthetic strategies

Genome mining reveals the biosynthetic potential of a novel Lysinibacillus zambalensis sp. nov., isolated from a hyperalkaline spring

A novel bacterium, designated as strain M3T, was isolated from a hyperalkaline spring in the Philippines and identified as a new species within the genus Lysinibacillus through 16 S rRNA gene sequence and genomic analyses. Although strain M3T shared a high 16 S rRNA gene sequence similarity (> 98.7%) with many Lysinibacillus species, the digital DNA-DNA hybridization and orthologous average nucleotide identity values between strain M3T and its closet relative, Lysinibacillus xylanilyticus DSM 23,493T, were 41.2% and 90.6%, respectively-both below the established threshold for prokaryotic species delineation. Genome mining of the 5.3 Mbp-draft genome of strain M3T revealed eight biosynthetic gene clusters, which shared little sequence similarity with characterized clusters, suggesting the potential for encoding novel specialized metabolites. The cells of strain M3T were Gram-stain-positive, aerobic, rod-shaped, non-motile, and capable of endospore formation. Optimum growth was observed at 30 °C, pH 8.0, and 0.5% (w/v) NaCl. The major respiratory quinone was menaquinone-7, and the predominant polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, and two unknown phospholipids. Its fatty acid profile showed an elevated level of iso-C15:0, and the peptidoglycan type was determined to be A4α (L-Lys-D-Asp). This study contributes to the growing database and understanding of the genus and aims to help drive future research on the bioactive potential of the genus. Lysinibacillus zambalensis sp. nov. is proposed with strain M3T as the type strain (= TISTR 10640T = BIOTECH 10973T).

Amphibian skin bacteria contain a wide repertoire of genes linked to their antifungal capacities

Emerging diseases caused by fungi are a serious threat to wildlife biodiversity. The widespread fungal pathogen Batrachochytrium dendrobatidis (Bd) has caused dramatic amphibian population declines and species extinctions worldwide. While many amphibians have been negatively affected by Bd, some populations/species have persisted despite its presence. One factor contributing to amphibian protection against this fungus is the host-associated skin microbiome. In this study, we aimed to identify gene clusters associated with the antifungal activity of amphibian skin bacteria. Specifically, we explored skin bacteria isolated from species that have persisted in the wild despite the presence of Bd: the frogs Agalychnis callidryas, Craugastor fitzingeri, Dendropsophus ebraccatus, and the axolotl Ambystoma altamirani. Bacterial isolates were tested in vitro for their capacity to inhibit the growth of two fungal pathogens: Bd and the phytopathogen Botrytis cinerea (Bc). Genome mining of these bacterial isolates revealed a diverse repertoire of Biosynthetic Gene Clusters (BGCs) and chitin-degrading gene families (ChDGFs) whose composition and abundance differed among bacterial families. We found specific BGCs and ChDGFs that were associated with the capacity of bacteria to inhibit the growth of either Bd or Bc, suggesting that distinct fungi could be inhibited by different molecular mechanisms. By using similarity networks and machine learning, we identified BGCs encoding known antifungal compounds such as viscosin, fengycin, zwittermicin, as well as siderophores and a novel family of beta-lactones. Finally, we propose that the diversity of BGCs found in amphibian skin bacteria comprise a substantial genetic reservoir that could collectively explain the antifungal properties of the amphibian skin microbiome.

Genome-informed Discovery of Monchicamides A-K: Cyanobactins from the Microcoleaceae Cyanobacterium LEGE 16532

Genome mining has emerged as an important tool for the discovery of natural products and is particularly effective for the swift identification of ribosomally synthesized and post-translationally modified peptides (RiPPs). Among RiPPs, cyanobactins have gained attention due to their diverse structures and bioactive properties. Here, we explored the Microcoleaceae cyanobacterium LEGE 16532 strain and identified the mon biosynthetic gene cluster (BGC), which was predicted to encode cyanobactin-like molecules. This led to the detection of 11 macrocyclic cyanobactins, the monchicamides, some of which feature mono- or diprenylation. One of the compounds was isolated, monchicamides I (9), and its planar structure was established by LC-HRESIMS/MS data as well as 1D and 2D NMR spectroscopy, confirming forward O-prenylation in Tyr. In addition, the absolute configuration of compound 9 was determined by Marfey's method and chiral-phase HPLC. The structures of the additional cyanobactins were proposed from MS/MS data analysis. The bioactivity profile of the isolated compound was also evaluated, but no cytotoxic, antimicrobial, or antiamoebic activity was observed.

A metabologenomics approach reveals the unexplored biosynthetic potential of bacteria isolated from an Amazon Conservation Unit

The Amazon, an important biodiversity hotspot, remains poorly explored in terms of its microbial diversity and biotechnological potential. The present study characterized the metabolic potential of Gram-positive strains of the Actinomycetes and Bacilli classes isolated from soil samples of an Amazon Conservation Unit. The sequencing of the 16S rRNA gene classified the strains ACT015, ACT016, and FIR094 within the genera Streptomyces, Rhodococcus, and Brevibacillus, respectively. Genome mining identified 33, 17, and 14 biosynthetic gene clusters (BGCs) in these strains, including pathways for the biosynthesis of antibiotic and antitumor agents. Additionally, 40 BGCs (62,5% of the total BGCs) were related to unknown metabolites. The OSMAC approach and untargeted metabolomics analysis revealed a plethora of metabolites under laboratory conditions, underscoring the untapped chemical diversity and biotechnological potential of these isolates. Our findings illustrated the efficacy of the metabologenomics approach in elucidating secondary metabolism and selecting BGCs with chemical novelty.IMPORTANCEThe largest rainforest in the world is globally recognized for its biodiversity. However, until now, few studies have been conducted to prospect natural products from the Amazon microbiome. In this work, we isolated three free-living bacterial species from the microbiome of pristine soils and used two high-throughput technologies to reveal the vast unexplored repertoire of secondary metabolites produced by these microorganisms.

Exploring Bioactive Fungal RiPPs: Advances, Challenges, and Future Prospects

Fungal ribosomally synthesized and post-translationally modified peptides (RiPPs) are a vital class of natural products known for their biological activities including anticancer, antitubulin, antinematode, and immunosuppressant properties. These bioactive fungal RiPPs play key roles in chemical ecology and have a significant therapeutic potential. Their structural diversity, which arises from intricate post-translational modifications of precursor peptides, is particularly remarkable. Despite their biological and ecological importance, the discovery of fungal RiPPs has been historically challenging and only a limited number have been identified. To date, known fungal RiPPs are primarily grouped into three groups: cycloamanides and borosins from basidiomycetes and dikaritins from ascomycetes. Recent advancements in bioinformatics have revealed the vast untapped potential of fungi to produce RiPPs, offering new opportunities for their discovery. This review highlights recent progress in fungal RiPP biosynthesis and genome-guided discovery strategies. We propose that combining the knowledge of fungal RiPP biosynthetic pathways with advanced gene-editing technologies and bioinformatic tools will significantly accelerate the discovery of novel bioactive fungal RiPPs.

Discovery, Biosynthesis, and Characterization of Rodencin, a Two-Component Lanthipeptide, Harboring d-Amino Acids Introduced by the Unusual Dehydrogenase RodJA

Lanthipeptides, a group of ribosomally synthesized and post-translationally modified peptides (RiPPs), exhibit diverse structures and bioactivities. Their biosynthetic enzymes serve as valuable tools for peptide bioengineering. Here, we report a class II lanthipeptide biosynthetic gene cluster in a Bacillus strain, driving the biosynthesis of a two-component lanthipeptide, termed rodencin, featured by the presence of two different d-amino acids, i.e., d-Ala and d-Abu. Rodencin displays synergistic antimicrobial activity against food-borne pathogens such as Bacillus cereus, Staphylococcus aureus, and Listeria monocytogenes. The α-peptide of rodencin contains one d-Ala and the β-peptide features both d-Ala and d-Abu. These are installed by dehydratases RodM1 and RodM2 and dehydrogenase RodJA, the activities of which were successfully reconstituted using a dedicated E. coli expression system. To illustrate the unusual d-Abu incorporation potential of the enzymes, analogous to the d-amino acid-containing β peptide of lacticin 3147, was successfully produced with the rodencin heterologous expression system, by employing RodM2 and the dehydrogenase RodJA.

Advances, opportunities, and challenges in methods for interrogating the structure activity relationships of natural products

Time span in literature: 1985-early 2024Natural products play a key role in drug discovery, both as a direct source of drugs and as a starting point for the development of synthetic compounds. Most natural products are not suitable to be used as drugs without further modification due to insufficient activity or poor pharmacokinetic properties. Choosing what modifications to make requires an understanding of the compound's structure-activity relationships. Use of structure-activity relationships is commonplace and essential in medicinal chemistry campaigns applied to human-designed synthetic compounds. Structure-activity relationships have also been used to improve the properties of natural products, but several challenges still limit these efforts. Here, we review methods for studying the structure-activity relationships of natural products and their limitations. Specifically, we will discuss how synthesis, including total synthesis, late-stage derivatization, chemoenzymatic synthetic pathways, and engineering and genome mining of biosynthetic pathways can be used to produce natural product analogs and discuss the challenges of each of these approaches. Finally, we will discuss computational methods including machine learning methods for analyzing the relationship between biosynthetic genes and product activity, computer aided drug design techniques, and interpretable artificial intelligence approaches towards elucidating structure-activity relationships from models trained to predict bioactivity from chemical structure. Our focus will be on these latter topics as their applications for natural products have not been extensively reviewed. We suggest that these methods are all complementary to each other, and that only collaborative efforts using a combination of these techniques will result in a full understanding of the structure-activity relationships of natural products.

Ribosomal peptides with polycyclic isoprenoid moieties

Isoprenoid modifications of proteins and peptides serve fundamental biological functions and are of therapeutic interest. While C15 (farnesyl) and C20 (geranylgeranyl) moieties are prevalent among proteins, known ribosomal peptide prenylations involve shorter-chain units not exceeding farnesyl in size. To our knowledge, cyclized terpene moieties have not been reported from either biomolecule class. Here we used targeted genome mining and heterologous pathway reconstitution to identify ribosomally synthesized and post-translationally modified peptides (RiPPs) with elaborate, cyclized geranylgeranyl modifications. The installing maturases commonly feature fused prenyltransferase-terpene cyclase architectures. We characterized two bifunctional maturases with distinct prenyltransferase folds and identified the terminal product of a cyanobacterial proteusin as an exceptionally complex pseudosteroid-annelated polycyclic peptide. Bioassays suggest modest anti-cyanobacterial activity with the modification being crucial for activity. Genome data predict cyclic isoprenoid units for various RiPP families including proteusin, Nif11, and lasso peptides and thus broader natural and biotechnological compatibility of the maturase system.

Opportunities and challenges of RiPP-based therapeutics

Covering: up to 2024Ribosomally synthesised and post-translationally modified peptides (RiPPs) comprise a substantial group of peptide natural products exhibiting noteworthy bioactivities ranging from antiinfective to anticancer and analgesic effects. Furthermore, RiPP biosynthetic pathways represent promising production routes for complex peptide drugs, and the RiPP technology is well-suited for peptide engineering to produce derivatives with specific functions. Thus, RiPP natural products possess features that render them potentially ideal candidates for drug discovery and development. Nonetheless, only a small number of RiPP-derived compounds have successfully reached the market thus far. This review initially outlines the therapeutic opportunities that RiPP-based compounds can offer, whilst subsequently discussing the limitations that require resolution in order to fully exploit the potential of RiPPs towards the development of innovative drugs.

Use of a head-to-tail peptide cyclase to prepare hybrid RiPPs

Cyclotides and lanthipeptides are cyclic peptide natural products with promising bioengineering potential. No peptides have been isolated that contain both structural motifs defining these two families, an N-to-C cyclised backbone and lanthionine linkages. We combined their biosynthetic machineries to produce hybrid structures that possess improved activity or stability, demonstrate how the AEP-1 plant cyclase can be utilised to complete the maturation of the sactipeptide subtilosin A, and present head-to-tail cyclisation of the glycocin sublancin. These studies show the plasticity of AEP-1 and its utilisation alongside other post-translational modifications.

Genome Mining for New Enzyme Chemistry

A revolution in the field of biocatalysis has enabled scalable access to compounds of high societal values using enzymes. The construction of biocatalytic routes relies on the reservoir of available enzymatic transformations. A review of uncharacterized proteins predicted from genomic sequencing projects shows that a treasure trove of enzyme chemistry awaits to be uncovered. This Review highlights enzymatic transformations discovered through various genome mining methods and showcases their potential future applications in biocatalysis.

Cheminformatics-Guided Cell-Free Exploration of Peptide Natural Products

There have been significant advances in the flexibility and power of in vitro cell-free translation systems. The increasing ability to incorporate noncanonical amino acids and complement translation with recombinant enzymes has enabled cell-free production of peptide-based natural products (NPs) and NP-like molecules. We anticipate that many more such compounds and analogs might be accessed in this way. To assess the peptide NP space that is directly accessible to current cell-free technologies, we developed a peptide parsing algorithm that breaks down peptide NPs into building blocks based on ribosomal translation logic. Using the resultant data set, we broadly analyze the biophysical properties of these privileged compounds and perform a retrobiosynthetic analysis to predict which peptide NPs could be directly synthesized in augmented cell-free translation reactions. We then tested these predictions by preparing a library of highly modified peptide NPs. Two macrocyclases, PatG and PCY1, were used to effect the head-to-tail macrocyclization of candidate NPs. This retrobiosynthetic analysis identified a collection of high-priority building blocks that are enriched throughout peptide NPs, yet they had not previously been tested in cell-free translation. To expand the cell-free toolbox into this space, we established, optimized, and characterized the flexizyme-enabled ribosomal incorporation of piperazic acids. Overall, these results demonstrate the feasibility of cell-free translation for peptide NP total synthesis while expanding the limits of the technology. This work provides a novel computational tool for exploration of peptide NP chemical space, that could be expanded in the future to allow design of ribosomal biosynthetic pathways for NPs and NP-like molecules.

Cyclic Peptides for Drug Development

Cyclic peptides are fascinating molecules abundantly found in nature and exploited as molecular format for drug development as well as other applications, ranging from research tools to food additives. Advances in peptide technologies made over many years through improved methods for synthesis and drug development have resulted in a steady stream of new drugs, with an average of around one cyclic peptide drug approved per year. Powerful technologies for screening random peptide libraries, and de novo generating ligands, have enabled the development of cyclic peptide drugs independent of naturally derived molecules and now offer virtually unlimited development opportunities. In this review, we feature therapeutically relevant cyclic peptides derived from nature and discuss the unique properties of cyclic peptides, the enormous technological advances in peptide ligand development in recent years, and current challenges and opportunities for developing cyclic peptides that address unmet medical needs.

Lipopeptides development in cosmetics and pharmaceutical applications: A comprehensive review

Lipopeptides are surface active, natural products of bacteria, fungi and green-blue algae origin, having diverse structures and functionalities. In analogy, a number of chemical synthesis techniques generated new designer lipopeptides with desirable features and functions. Lipopetides are self-assembly guided, supramolecular compounds which have the capacity of high-density presentation of the functional epitopes at the surface of the nanostructures. This feature contributes to their successful application in several industry sectors, including food, feed, personal care, and pharmaceutics. In this comprehensive review, the novel class of ribosomally synthesized lipopeptides is introduced alongside the more commonly occuring non-ribosomal lipopeptides. We highlight key representatives of the most researched as well as recently described lipopeptide families, with emphasis on structural features, self-assembly and associated functions. The common biological, chemical and hybrid production routes of lipopeptides, including prominent analogues and derivatives are also discussed. Furthermore, genetic engineering strategies aimed at increasing lipopeptide yields, diversity and biological activity are summarized and exemplified. With respect to application, this work mainly details the potential of lipopeptides in personal care and cosmetics industry as cleansing agents, moisturizer, anti-aging/anti-wrinkling, skin whitening and preservative agents as well as the pharmaceutical industry as anitimicrobial agents, vaccines, immunotherapy, and cancer drugs. Given that this review addresses human applications, we conclude on the topic of safety of lipopeptide formulations and their sustainable production.

Multiple cry Genes in Bacillus thuringiensis Strain BTG Suggest a Broad-Spectrum Insecticidal Activity

The properties of Bacillus thuringiensis strains as a biopesticide with potent action against moths, beetles, and mosquitoes have been known for decades, with individual subspecies showing specific activity against a particular pest. The aim of the present work is to characterize strains that can be used for broad-spectrum pest control in agriculture. Twenty strains of B. thuringiensis were isolated from Bulgarian soil habitats. The strains were screened for genes encoding 12 different crystal (Cry) endotoxins by PCR with specific primer pairs. Seven of the isolates contained cry genes in their genomes. B. thuringiensis strains PL1, PL3, and PL20 contained at least three different cry genes, while B. thuringiensis serovar galleriae BTG contained at least four. Moreover, scanning electron microscopy (SEM) investigation revealed the production of bipyramidal (PL1, PL3, PL20), polygonal (PL1), cubic (BTG), and spherical crystals (BTG and PL20). Potentially containing the most cry genes, the BTG genome was sequenced and annotated. It comprises 6,275,416 base pairs, does not contain plasmids, has a GC content of 35.05%, and contained 7 genes encoding crystal toxins: cry1Ab35, cry1Db, cry1Fb, cry1Ib, cry2Ab, cry8Ea1, and cry9Ba. This unique combination would possibly enable the simultaneous pesticidal action against pest species from orders Lepidoptera, Coleoptera, Diptera, and Hemiptera, as well as class Gastropoda. Whole-genome sequencing provided accurate information about the presence, localization, and classification of Cry toxins in B. thuringiensis BTG, revealing the great potential of the strain for the development of new broad-spectrum bio-insecticides.

Beyond 20 in the 21st Century: Prospects and Challenges of Non-canonical Amino Acids in Peptide Drug Discovery

Life is constructed primarily using a toolbox of 20 canonical amino acids-relying upon these building blocks for the assembly of proteins and peptides that regulate nearly every cellular task, including cell structure, function, and maintenance. While Nature continues to be a source of inspiration for drug discovery, medicinal chemists are not beholden to only 20 canonical amino acids and have begun to explore non-canonical amino acids (ncAAs) for the construction of designer peptides with improved drug-like properties. However, as our toolbox of ncAAs expands, drug hunters are encountering new challenges in approaching the iterative peptide design-make-test-analyze cycle with a seemingly boundless set of building blocks. This Microperspective focuses on new technologies that are accelerating ncAA interrogation in peptide drug discovery (including HELM notation, late-stage functionalization, and biocatalysis) while shedding light on areas where further investment could not only accelerate the discovery of new medicines but also improve downstream development.