Discovery, biochemical characterization, and bioengineering of cyanobactin prenyltransferases

Prenylated bacterial natural products: occurrence, chemical diversity, biosynthesis and bioactivity

Covering: 2000 to 2024Prenylated bacterial natural products (NPs), catalyzed by cluster-situated prenyltransferases (PTs), exhibit large structural diversity and broad biological activities and have received increasing attention for novel drug discovery and development. This review provides a comprehensive summary of the recent progress in the investigation of prenylated bacterial NPs. To highlight the structural and chemical space of prenylated bacterial NPs, we discuss their occurrence, structures, biosynthesis and bioactivities. Representative examples are summarized with illustrations of PT-catalyzed biosynthetic pathways of distinct NP classes, which present new opportunities for the discovery of novel prenylated bacterial NPs. The mechanistic study of PTs involved in bacterial NP biosynthesis has been outlined, and prenylated bacterial NPs hold great promise as novel biocatalysts for the synthesis of novel drug leads in modern medicine.

Design and Production of Geranylated Cyclic Peptides by the RiPP Enzymes SyncM and PirF

The growing threat of antibiotic resistance highlights the urgent need for new antimicrobial agents. Nonribosomal peptides (NRPs) are potent antibiotics with complex structures, but generating novel NRP analogues is costly and inefficient. An emerging alternative is using ribosomally synthesized and post-translationally modified peptides (RiPPs), which are gene-encoded, allowing for easier mutagenesis and modification. This study aimed to produce peptides with two key structural elements of many NRP antibiotics: a macrocycle and an N-terminal lipid moiety. The RiPP enzymes SyncM and PirF were employed-SyncM introduced lanthionine or methyllanthionine macrocycles, while PirF incorporated isoprenyl chains to emulate the lipid moieties in NRPs. Both enzymes successfully modified the templates, and their combined use generated lipidated macrocyclic peptides, resembling lipopeptide antibiotics. These findings demonstrate the potential of SyncM and PirF as versatile tools for designing novel gene-encoded NRP mimics, enabling high-throughput screening for new bioactive peptides.

Efficient Biosynthesis of 8-Prenylkaempferol from Kaempferol by Using Flavonoid 8-Dimethylallyltransferase Derived from Epimedium koreanum

The genus Epimedium includes popular Chinese medicinal plants, and icariin and its precursor icaritin are the key bioactive components of Epimedium. Here, we identified flavonoid 8-dimethylallyltransferase (F8DT) in the authentic medicinal material of Epimedium koreanum, which is a key gene in the icariin biosynthesis pathway. This enzyme can catalyze the synthesis of 8-prenylkaempferol (8PK) from kaempferol. The catalytic ability of the rate-limiting enzyme EkF8DT was significantly improved by truncating its N-terminal intrinsically disordered regions (IDRs) and enhancing the flux of the mevalonate pathway. Icaritin was also successfully synthesized by introducing flavonoid 4'-O-methyltransferase into the Saccharomyces cerevisiae strain. Finally, the highest production of 8PK and icaritin (3.6 g/L and 172.0 mg/L, respectively) was obtained in the S. cerevisiae strain.

Prenylation of Flavanones by an Aromatic Prenyltransferase from Fusarium globosum

Prenylation increases the structural diversity and biological activity of flavonoids. In this study, an aromatic prenyltransferase, FgPT1, was identified from Fusarium globosum. This enzyme was demonstrated to specifically catalyze the prenylation of flavanones, including naringenin, hesperitin, eriodictyol, liquiritigenin, rac-pinocembrin, and dihydrogenistein, and exhibited no activity toward other types of flavonoids, including chalcones, flavonols, isoflavonoids, and flavonols. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and nuclear magnetic resonance (NMR) analysis indicated that the majority of prenylated products were 6-C prenyl flavanones, with the exception of liquiritigenin, which was additionally transformed to 4'-O prenyl liquiritigenin. Enzyme kinetic analysis suggested that FgPT1 exhibited the highest catalytic efficiency towards naringenin, with a kcat/KM value determined as 61.92 s-1 M-1, and the lowest catalytic efficiency towards liquiritigenin, with a kcat/KM of 1.18 s-1 M-1. Biochemical characterization suggested that FgPT1 functioned as a metal-dependent enzyme with optimal activity in the presence of Ba2+ at pH 7.5 and 30 °C. Site-directed mutagenesis resulted in a series of mutants, including A325V with impaired prenylation activity and V116I, V181I, and V194I with enhanced activity. V194I displayed the highest enzymatic activity with a nine-fold increase compared to wild-type FgPT1.

Geranylation of Cyclic Dipeptides and Naphthols by the Fungal Prenyltransferase CdpC3PT_F253G

Prenyl modification often improves the biological activities of compounds. Prenyltransferases have attracted attention as environmentally friendly biocatalysts for catalyzing prenyl modification of compounds. Compared to dimethylallyl modifications, research on geranyl modifications is relatively limited. To enrich biocatalytic toolboxes for generating potentially bioactive geranylated derivatives, this study developed methodologies to synthesize two types of geranylated compounds, i. e., geranylated tryptophan-containing cyclic dipeptides and geranylated naphthols, employing the F253G mutant of CdpC3PT, a cyclic dipeptide prenyltransferase from Neosartorya fischeri. The cyclic dipeptides (1-3) were transformed into C7-geranylated products (1G1-3G1), whereas 1-naphthol (4) and derivatives (5-6) yielded C4-geranylated products (4G1-6G1) and 2,7-dihydroxynaphthalene (7) generated a C3-geranylated product (7G1). All seven substrates and their geranylated products underwent antibacterial efficacy testing against Bacillus subtilis. Among them, five geranylated compounds (2G1 and 4G1-7G1) demonstrated antibacterial efficacies against Bacillus subtilis, with MIC values ranging from 4 to 32 μg/mL, surpassing their non-geranylated precursors. This research broadens the tools of geranyl-modifying biocatalysts, illustrates a case for developing highly efficient or function-altered biocatalysts and showcases the potential of prenyltransferases in the biosynthesis of bioactive small molecules.

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.

Modifications of Prenyl Side Chains in Natural Product Biosynthesis

In recent years, there has been a growing interest in understanding the enzymatic machinery responsible for the modifications of prenyl side chains and elucidating their roles in natural product biosynthesis. This interest stems from the pivotal role such modifications play in shaping the structural and functional diversity of natural products, as well as from their potential applications to synthetic biology and drug discovery. In addition to contributing to the diversity and complexity of natural products, unique modifications of prenyl side chains are represented by several novel biosynthetic mechanisms. Representative unique examples of epoxidation, dehydrogenation, oxidation of methyl groups to carboxyl groups, unusual C-C bond cleavage and oxidative cyclization are summarized and discussed. By revealing the intriguing chemistry and enzymology behind these transformations, this comprehensive and comparative review will guide future efforts in the discovery, characterization and application of modifications of prenyl side chains in natural product biosynthesis.

Biocatalytic Ether Lipid Synthesis by an Archaeal Glycerolprenylase

Although ethers are common in secondary natural products, they are an underrepresented functional group in primary metabolism. As such, there are comparably few enzymes capable of constructing ether bonds in a general fashion. However, such enzymes are highly sought after for synthetic applications as they typically operate with higher regioselectivity and under milder conditions than traditional organochemical approaches. To expand the repertoire of well characterized ether synthases, we herein report on a promiscuous archaeal prenyltransferase from the scarcely researched family of geranylgeranylglyceryl phosphate synthases (GGGPSs or G3PSs). We show that the ultrastable Archaeoglobus fulgidus G3PS makes various (E)- and (Z)-configured prenyl glycerol ethers from the corresponding pyrophosphates while exerting perfect control over the configuration at the glycerol unit. Based on experimental and computational data, we propose a mechanism for this enzyme which involves an intermediary prenyl carbocation equivalent. As such, this study provides the fundamental understanding and methods to introduce G3PSs into the biocatalytic alkylation toolbox.

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.

De Novo Discovery of Pseudo-Natural Prenylated Macrocyclic Peptide Ligands

Prenylation of peptides is widely observed in the secondary metabolites of diverse organisms, granting peptides unique chemical properties distinct from proteinogenic amino acids. Discovery of prenylated peptide agents has largely relied on isolation or genome mining of naturally occurring molecules. To devise a platform technology for de novo discovery of artificial prenylated peptides targeting a protein of choice, here we have integrated the thioether-macrocyclic peptide (teMP) library construction/selection technology, so-called RaPID (Random nonstandard Peptides Integrated Discovery) system, with a Trp-C3-prenyltransferase KgpF involved in the biosynthesis of a prenylated natural product. This unique enzyme exhibited remarkably broad substrate tolerance, capable of modifying various Trp-containing teMPs to install a prenylated residue with tricyclic constrained structure. We constructed a vast library of prenylated teMPs and subjected it to in vitro selection against a phosphoglycerate mutase. This selection platform has led to the identification of a pseudo-natural prenylated teMP inhibiting the target enzyme with an IC50 of 30 nM. Importantly, the prenylation was essential for the inhibitory activity, enhanced serum stability, and cellular uptake of the peptide, highlighting the benefits of peptide prenylation. This work showcases the de novo discovery platform for pseudo-natural prenylated peptides, which is readily applicable to other drug targets.

Cell-Free Systems: Ideal Platforms for Accelerating the Discovery and Production of Peptide-Based Antibiotics

Peptide-based antibiotics (PBAs), including antimicrobial peptides (AMPs) and their synthetic mimics, have received significant interest due to their diverse and unique bioactivities. The integration of high-throughput sequencing and bioinformatics tools has dramatically enhanced the discovery of enzymes, allowing researchers to identify specific genes and metabolic pathways responsible for producing novel PBAs more precisely. Cell-free systems (CFSs) that allow precise control over transcription and translation in vitro are being adapted, which accelerate the identification, characterization, selection, and production of novel PBAs. Furthermore, these platforms offer an ideal solution for overcoming the limitations of small-molecule antibiotics, which often lack efficacy against a broad spectrum of pathogens and contribute to the development of antibiotic resistance. In this review, we highlight recent examples of how CFSs streamline these processes while expanding our ability to access new antimicrobial agents that are effective against antibiotic-resistant infections.

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.

Tryptophan-Centric Bioinformatics Identifies New Lasso Peptide Modifications

Lasso peptides are a class of ribosomally synthesized and post-translationally modified peptides (RiPPs) defined by a macrolactam linkage between the N-terminus and the side chain of an internal aspartic acid or glutamic acid residue. Instead of adopting a branched-cyclic conformation, lasso peptides are "threaded", with the C-terminal tail passing through the macrocycle to present a kinetically trapped rotaxane conformation. The availability of enhanced bioinformatics methods has led to a significant increase in the number of secondary modifications found on lasso peptides. To uncover new ancillary modifications in a targeted manner, a bioinformatic strategy was developed to discover lasso peptides with modifications to tryptophan. This effort identified numerous putative lasso peptide biosynthetic gene clusters with core regions of the precursor peptides enriched in tryptophan. Parsing of these tryptophan (Trp)-rich biosynthetic gene clusters uncovered several putative ancillary modifying enzymes, including halogenases and dimethylallyltransferases expected to act upon Trp. Characterization of two gene products yielded a lasso peptide with two 5-Cl-Trp modifications (chlorolassin) and another bearing 5-dimethylallyl-Trp and 2,3-didehydro-Tyr modifications (wygwalassin). Bioinformatic analysis of the requisite halogenase and dimethylallyltransferase revealed numerous other putative Trp-modified lasso peptides that remain uncharacterized. We anticipate that the Trp-centric strategy reported herein may be useful in discovering ancillary modifications for other RiPP classes and, more generally, guide the functional prediction of enzymes that act on specific amino acids.

Structure Prediction and Genome Mining-Aided Discovery of the Bacterial C-Terminal Tryptophan Prenyltransferase PalQ

Post-translational prenylations, found in eukaryotic primary metabolites and bacterial secondary metabolites, play crucial roles in biomolecular interactions. Employing genome mining methods combined with AlphaFold2-based predictions of protein interactions, PalQ , a prenyltransferase responsible for the tryptophan prenylation of RiPPs produced by Paenibacillus alvei, is identified. PalQ differs from cyanobactin prenyltransferases because of its evolutionary relationship to isoprene synthases, which enables PalQ to transfer extended prenyl chains to the indole C3 position. This prenylation introduces structural diversity to the tryptophan side chain and also leads to conformational dynamics in the peptide backbone, attributed to the cis/trans isomerization that arises from the formation of a pyrrolidine ring. Additionally, PalQ exhibited pronounced positional selectivity for the C-terminal tryptophan. Such enzymatic characteristics offer a toolkit for peptide therapeutic lipidation.

Switching Prenyl Donor Specificities of Cyanobactin Prenyltransferases

Prenyltransferases in cyanobactin biosynthesis are of growing interest as peptide alkylation biocatalysts, but their prenylation modes characterized so far have been limited to dimethylallylation (C5) or geranylation (C10). Here we engaged in structure-guided engineering of the prenyl-binding pocket of a His-C2-geranyltransferase LimF to modulate its prenylation mode. Contraction of the pocket by a single mutation led to a His-C2-dimethylallyltransferase. More importantly, pocket expansion by a double mutation successfully repurposed LimF for farnesylation (C15), which is an unprecedented mode in this family. Furthermore, the obtained knowledge of the essential residues to construct the farnesyl-binding pocket has allowed for rational design of a Tyr-O-farnesyltransferase by a triple mutation of a Tyr-O-dimethylallyltransferase PagF. These results provide an approach to manipulate the prenyl specificity of cyanobactin prenyltransferases, broadening the chemical space covered by this class of enzymes and expanding the toolbox of peptide alkylation biocatalysts.