Lineage-Specific CYP80 Expansion and Benzylisoquinoline Alkaloid Diversity in Early-Diverging Eudicots

Menispermaceae species, as early-diverging eudicots, can synthesize valuable benzylisoquinoline alkaloids (BIAs) like bisbenzylisoquinoline alkaloids (bisBIAs) and sinomenines with a wide range of structural diversity. However, the evolutionary mechanisms responsible for their chemo-diversity are not well understood. Here, a chromosome-level genome assembly of Menispermum dauricum is presented and demonstrated the occurrence of two whole genome duplication (WGD) events that are shared by Ranunculales and specific to Menispermum, providing a model for understanding chromosomal evolution in early-diverging eudicots. The biosynthetic pathway for diverse BIAs in M. dauricum is reconstructed by analyzing the transcriptome and metabolome. Additionally, five catalytic enzymes - one norcoclaurine synthase (NCS) and four cytochrome P450 monooxygenases (CYP450s) - from M. dauricum are responsible for the formation of the skeleton, hydroxylated modification, and C-O/C-C phenol coupling of BIAs. Notably, a novel leaf-specific MdCYP80G10 enzyme that catalyzes C2'-C4a phenol coupling of (S)-reticuline into sinoacutine, the enantiomer of morphinan compounds, with predictable stereospecificity is discovered. Moreover, it is found that Menispermum-specific CYP80 gene expansion, as well as tissue-specific expression, has driven BIA diversity in Menispermaceae as compared to other Ranunculales species. This study sheds light on WGD occurrences in early-diverging eudicots and the evolution of diverse BIA biosynthesis.

Metabolomic Approaches in Assessing the Insecticidal Activity of the Extracts from Argemone ochroleuca Sweet (Papaveraceae) Against Three Diverse Crop Pests of Economic Importance

For years, crop protection from pest attack, has been dominated by the use of synthetic insecticides. However, many of them can cause severe environmental problems and human health. In this context, the use of plant extracts constitutes an alternative to avoid this kind of contaminants. In this work, we investigated the chemical constituents and insecticidal activity of different extracts of leaves and stems of Argemone ochroleuca Sweet (Papaveraceae) against three economically important pests Sitophilos zeamais (Coleoptera:Curculionidae), Galleria mellonella (Lepidoptera:Pyralidae) and Xyleborus ferrugineus (Coleoptera:Scolytidae). A GC-MS analysis mostly revealed the presence benzylisoquinoline alkaloids such as allocryptopine, protopine, among others. For the insecticidal activity, after nine hours of contact, the methanolic leaves extract showed a 100 % of mortality, followed by the dichloromethane stems extract with up to 93 % of mortality. The results suggest that the benzylisoquinoline alkaloids are involved in the insecticidal activity through the octopaminergic system of the tested insects.

Corrigendum: Stylopine: a potential natural metabolite to block vascular endothelial growth factor receptor 2 (VEGFR2) in osteosarcoma therapy

[This corrects the article DOI: 10.3389/fphar.2023.1150270.].

The CYP80A and CYP80G Are Involved in the Biosynthesis of Benzylisoquinoline Alkaloids in the Sacred Lotus (Nelumbo nucifera)

Bisbenzylisoquinoline and aporphine alkaloids are the two main pharmacological compounds in the ancient sacred lotus (Nelumbo nucifera). The biosynthesis of bisbenzylisoquinoline and aporphine alkaloids has attracted extensive attention because bisbenzylisoquinoline alkaloids have been reported as potential therapeutic agents for COVID-19. Our study showed that NnCYP80A can catalyze C-O coupling in both (R)-N-methylcoclaurine and (S)-N-methylcoclaurine to produce bisbenzylisoquinoline alkaloids with three different linkages. In addition, NnCYP80G catalyzed C-C coupling in aporphine alkaloids with extensive substrate selectivity, specifically using (R)-N-methylcoclaurine, (S)-N-methylcoclaurine, coclaurine and reticuline as substrates, but the synthesis of C-ring alkaloids without hydroxyl groups in the lotus remains to be elucidated. The key residues of NnCYP80G were also studied using the 3D structure of the protein predicted using Alphafold 2, and six key amino acids (G39, G69, A211, P288, R425 and C427) were identified. The R425A mutation significantly decreased the catalysis of (R)-N-methylcoclaurine and coclaurine inactivation, which might play important role in the biosynthesis of alkaloids with new configurations.

Phylogenetic analysis and functional characterization of norcoclaurine synthase involved in benzylisoquinoline alkaloids biosynthesis in Stephania tetrandra

Benzylisoquinoline alkaloids (BIAs) are a class of secondary metabolites that possess diverse pharmaceutical properties and are exclusively accumulated in specific plant genera. The Pictet-Spengler condensation, catalyzed by norcoclaurine synthase (NCS), represents a key enzymatic reaction in the biosynthetic pathway of BIAs. While NCS genes have been identified in several plant families such as Papaveraceae, Berberidaceae, and Ranunculaceae, no NCS genes have been reported in Menispermaceae, which is another genus known to accumulate BIAs. Here, NCSs were isolated and functionally characterized from the Menispermaceae family plant Stephania tetrandra. In vitro enzyme assay identified two functional StNCSs which could catalyze the formation of (S)-norcoclaurine. These functionally characterized genes were then integrated into engineered yeast to enable the production of norcoclaurine. Phylogenetic analysis of the NCS enzymes revealed that the StNCSs predominantly clustered into two clades. The functional StNCSs clustered with known NCSs, highlighting the presence of a specific NCS catalytic domain. This study not only provides additional genetic components for the synthetic biology-based production of BIAs in yeast but also contributes to the understanding of the phylogenetic relationships and structure-function relationship of NCS genes involved in the origin and production of BIAs.

Rational Engineering of (S)-Norcoclaurine Synthase for Efficient Benzylisoquinoline Alkaloids Biosynthesis

(S)-Norcoclaurine is synthesized in vivo through a metabolic pathway that ends with (S)-norcoclaurine synthase (NCS). The former constitutes the scaffold for the biosynthesis of all benzylisoquinoline alkaloids (BIAs), including many drugs such as the opiates morphine and codeine and the semi-synthetic opioids oxycodone, hydrocodone, and hydromorphone. Unfortunately, the only source of complex BIAs is the opium poppy, leaving the drug supply dependent on poppy crops. Therefore, the bioproduction of (S)-norcoclaurine in heterologous hosts, such as bacteria or yeast, is an intense area of research nowadays. The efficiency of (S)-norcoclaurine biosynthesis is strongly dependent on the catalytic efficiency of NCS. Therefore, we identified vital NCS rate-enhancing mutations through the rational transition-state macrodipole stabilization method at the Quantum Mechanics/Molecular Mechanics (QM/MM) level. The results are a step forward for obtaining NCS variants able to biosynthesize (S)-norcoclaurine on a large scale.

Erratum: Stylopine: a potential natural metabolite to activate vascular endothelial growth factor receptor 2 (VEGFR2) in osteosarcoma therapy

[This corrects the article DOI: 10.3389/fphar.2023.1150270.].

Stylopine: A potential natural metabolite to block vascular endothelial growth factor receptor 2 (VEGFR2) in osteosarcoma therapy

Vascular endothelial growth factor (VEGF) signals cell survival, cell migration, osteogenesis, cell proliferation, angiogenesis, and vascular permeability by binding to VEGF receptor 2 (VEGFR-2). Osteosarcoma is the most common primary bone cancer, majorly affects young adults. Activation of VEGFR-2 signaling is a therapeutic target for osteosarcoma. The present study aimed to evaluate the potency of stylopine in regulation of the VEGFR-2 signaling pathway and its anti-tumour effect human MG-63 osteosarcoma cells. The in silico study on benzylisoquinoline alkaloids was carried out for analyzing and shortlisting of compounds using a virtual screening, Lipinski's rule, bioavailability graphical RADAR plot, pharmacokinetics, toxicity, and molecular docking studies. Among the benzylisoquinoline alkaloids, stylopine was selected and subjected to in-vitro studies against human MG-63 osteosarcoma cells. Various experiments such as MTT assay, EtBr/AO staining, mitochondrial membrane potential assessment, transwell migration assay, gene expression analysis by a quantitative real time polymerase chain reaction (qRT-PCR) method, SDS-PAGE followed by immunoblotting were performed to evaluate its anti-tumour effect as compared to standard axitinib. The MTT assay indicates that stylopine inhibits cell proliferation in MG-63 cells. Similarly, as confirmed by the EtBr/Ao staining method, the MMP assay indicates that stylopine induces mitochondrial membrane damage and apoptosis as compared to axitinib. Moreover, stylopine inhibits the VEGF-165 induced MG-63 cell migration by a trans-well migration assay. The immunoblotting and qRT-PCR analysis showed that stylopine inhibits the VEGF-165 induced VEGFR2 expression in MG-63 cells. It is concluded that stylopine has potential to regulate VEGFR2 and can inhibit osteosarcoma cells to offer a new drug candidate for the treatment of bone cancer in future.

Characterization of benzylisoquinoline alkaloid methyltransferases in Liriodendron chinense provides insights into the phylogenic basis of angiosperm alkaloid diversity

Benzylisoquinoline alkaloids (BIAs) are a class of plant secondary metabolites with great pharmacological value. Their biosynthetic pathways have been extensively elucidated in the species from the Ranunculales order, such as poppy and Coptis japonica, in which methylation events play central roles and are directly responsible for BIA chemodiversity. Here, we combined BIA quantitative profiling and transcriptomic analyses to identify novel BIA methyltransferases (MTs) from Liriodendron chinense, a basal angiosperm plant. We identified an N-methyltransferase (LcNMT1) and two O-methyltransferases (LcOMT1 and LcOMT3), and characterized their biochemical functions in vitro. LcNMT1 methylates (S)-coclaurine to produce mono- and dimethylated products. Mutagenesis experiments revealed that a single-residue alteration is sufficient to change its substrate selectivity. LcOMT1 methylates (S)-norcoclaurine at the C6 site and LcOMT3 methylates (S)-coclaurine at the C7 site, respectively. Two key residues of LcOMT3, A115 and T301, are identified as important contributors to its catalytic activity. Compared with Ranunculales-derived NMTs, Magnoliales-derived NMTs were less abundant and had narrower substrate specificity, indicating that NMT expansion has contributed substantially to BIA chemodiversity in angiosperms, particularly in Ranunculales species. In summary, we not only characterized three novel enzymes that could be useful in the biosynthetic production of valuable BIAs but also shed light on the molecular origin of BIAs during angiosperm evolution.

Cyclopeptide alkaloids from Discaria chacaye (Rhamnaceae) as result of symbiosis with Frankia (Actinomycetales)

Cyclopeptide alkaloids with different biological activities are present in plants of the family Rhamnaceae. Plants of this family grow in a symbiotic relationship with aerobic Gram-positive actinomycetes belonging to the genus Frankia . This goal of this research was a study of the comparative profile of alkaloids present in Discaria chacaye and to establish a connection between the presence or absence of Frankia sp. and the alkaloids. In addition, insecticidal activities of the alkaloidal extract were examined. A total of 24 alkaloids were identified, of which 12 have a benzylisoquinoline skeleton, 9 were cyclopeptides, 2 isoquinolines, and 1 an aporphine. The presence of cyclopeptide alkaloids is associated with Frankia nodules in the plant root. The alkaloid extracts showed insecticidal activity with mortality dose-dependence and LD 50 values between 44 to 71 µg/mL.

The genome of Corydalis reveals the evolution of benzylisoquinoline alkaloid biosynthesis in Ranunculales

Species belonging to the order Ranunculales have attracted much attention because of their phylogenetic position as a sister group to all other eudicot lineages and their ability to produce unique yet diverse benzylisoquinoline alkaloids (BIAs). The Papaveraceae family in Ranunculales is often used as a model system for studying BIA biosynthesis. Here, we report the chromosome-level genome assembly of Corydalis tomentella, a species of Fumarioideae, one of the two subfamilies of Papaveraceae. Based on comparisons of sequenced Ranunculalean species, we present clear evidence of a shared whole-genome duplication (WGD) event that has occurred before the divergence of Ranunculales but after its divergence from other eudicot lineages. The C. tomentella genome enabled us to integrate isotopic labeling and comparative genomics to reconstruct the BIA biosynthetic pathway for both sanguinarine biosynthesis shared by papaveraceous species and the cavidine biosynthesis that is specific to Corydalis. Also, our comparative analysis revealed that gene duplications, especially tandem gene duplications, underlie the diversification of BIA biosynthetic pathways in Ranunculales. In particular, tandemly duplicated berberine bridge enzyme-like genes appear to be involved in cavidine biosynthesis. In conclusion, our study of the C. tomentella genome provides important insights into the occurrence of WGDs during the early evolution of eudicots, as well as into the evolution of BIA biosynthesis in Ranunculales.

Transport engineering using tobacco transporter NtJAT1 enhances alkaloid production in Escherichia coli

Transporters have been used in the production of plant metabolites in microorganisms. This study introduced a tobacco multidrug and toxic compound extrusion transporter, NtJAT1, into alkaloid-producing Escherichia coli cells. NtJAT1 expression enhanced alkaloid production secretion into the medium by 14 folds. Our findings further demonstrate the usefulness of the transport-engineering approach.

Complete biosynthesis of the bisbenzylisoquinoline alkaloids guattegaumerine and berbamunine in yeast

This work demonstrates microbial biosynthesis of bisbenzylisoquinoline (bisBIA) alkaloids. We show that several didomain epimerases can function in yeast to epimerize the nonnative substrate N-methylcoclaurine, an essential step in bisBIA biosynthesis. The N-methylcoclaurine epimerase activity was increased 10-fold by combining individual reductase and oxidase domains from different plant species. Strain engineering and optimization of media and growth conditions increased the bisBIA titer over 10,000-fold. We show that strains can be engineered to primarily produce one bisBIA product by selection of the cytochrome P450 variant that couples the monomer BIA subunits. We then leverage our bisBIA biosynthetic strain as a platform for the screening of other plant enzymes to produce two additional plant natural products de novo in a heterologous host.

Benzylisoquinoline alkaloids (BIAs) are a diverse class of medicinal plant natural products. Nearly 500 dimeric bisbenzylisoquinoline alkaloids (bisBIAs), produced by the coupling of two BIA monomers, have been characterized and display a range of pharmacological properties, including anti-inflammatory, antitumor, and antiarrhythmic activities. In recent years, microbial platforms have been engineered to produce several classes of BIAs, which are rare or difficult to obtain from natural plant hosts, including protoberberines, morphinans, and phthalideisoquinolines. However, the heterologous biosyntheses of bisBIAs have thus far been largely unexplored. Here, we describe the engineering of yeast strains that produce the Type I bisBIAs guattegaumerine and berbamunine de novo. Through strain engineering, protein engineering, and optimization of growth conditions, a 10,000-fold improvement in the production of guattegaumerine, the major bisBIA pathway product, was observed. By replacing the cytochrome P450 used in the final coupling reaction with a chimeric variant, the product profile was inverted to instead produce solely berbamunine. Our highest titer engineered yeast strains produced 108 and 25 mg/L of guattegaumerine and berbamunine, respectively. Finally, the inclusion of two additional putative BIA biosynthesis enzymes, SiCNMT2 and NnOMT5, into our bisBIA biosynthetic strains enabled the production of two derivatives of bisBIA pathway intermediates de novo: magnocurarine and armepavine. The de novo heterologous biosyntheses of bisBIAs presented here provide the foundation for the production of additional medicinal bisBIAs in yeast.

Alkaloid Biosynthesis in the Early Stages of the Germination of Argemone mexicana L. (Papaveraceae)

The synthesis of the benzylisoquinoline alkaloids, sanguinarine and berberine, was monitored in Argemone mexicana L. (Papaveracea) throughout the early stages of its hypocotyl and seedling development. Sanguinarine was detected in the cotyledons right after hypocotyl emergence, and it increased continuously until the apical hook unbent, prior to the cotyledonary leaves unfolding, when it abruptly fell. In the cotyledonary leaves, it also remained at low levels. Throughout development, berberine accumulation required the formation of cotyledonary leaves, whereas it was quickly detected in the hypocotyl from the time it emerged. Interestingly, the alkaloids detected in the cotyledons could have been imported from hypocotyls, because no transcriptional activity was detected in there. However, after turning into cotyledonary leaves, important levels of gene expression were noted. Taken together, these results suggest that the patterns of alkaloid tissue distribution are established from very early development, and might require transport systems.

Recent Advances in Metabolically Engineered Microorganisms for the Production of Aromatic Chemicals Derived From Aromatic Amino Acids

Aromatic compounds derived from aromatic amino acids are an important class of diverse chemicals with a wide range of industrial and commercial applications. They are currently produced via petrochemical processes, which are not sustainable and eco-friendly. In the past decades, significant progress has been made in the construction of microbial cell factories capable of effectively converting renewable carbon sources into value-added aromatics. Here, we systematically and comprehensively review the recent advancements in metabolic engineering and synthetic biology in the microbial production of aromatic amino acid derivatives, stilbenes, and benzylisoquinoline alkaloids. The future outlook concerning the engineering of microbial cell factories for the production of aromatic compounds is also discussed.

Over 100 Million Years of Enzyme Evolution Underpinning the Production of Morphine in the Papaveraceae Family of Flowering Plants

Phylogenomic analysis of whole genome sequences of five benzylisoquinoline alkaloid (BIA)-producing species from the Ranunculales and Proteales orders of flowering plants revealed the sequence and timing of evolutionary events leading to the diversification of these compounds. (S)-Reticuline is a pivotal intermediate in the synthesis of many BIAs and our analyses revealed parallel evolution between the two orders, which diverged ∼122 million years ago (MYA). Berberine is present in species across the entire Ranunculales, and we found co-evolution of genes essential for production of the protoberberine class. The benzophenanthridine class, which includes the antimicrobial compound sanguinarine, is specific to the Papaveraceae family of Ranunculales, and biosynthetic genes emerged after the split with the Ranunculaceae family ∼110 MYA but before the split of the three Papaveraceae species used in this study at ∼77 MYA. The phthalideisoquinoline noscapine and morphinan class of BIAs are exclusive to the opium poppy lineage. K_s estimation of paralogous pairs indicates that morphine biosynthesis evolved more recently than 18 MYA in the Papaver genus. In the preceding 100 million years gene duplication, neofunctionalization and recruitment of additional enzyme classes, combined with gene clustering, gene fusion, and gene amplification, resulted in emergence of medicinally valuable BIAs including morphine and noscapine.

Isolation and characterization of two O-methyltransferases involved in benzylisoquinoline alkaloid biosynthesis in sacred lotus (Nelumbo nucifera)

Benzylisoquinoline alkaloids (BIAs) are a major class of plant metabolites with many pharmacological benefits. Sacred lotus (Nelumbo nucifera) is an ancient aquatic plant of medicinal value because of antiviral and immunomodulatory activities linked to its constituent BIAs. Although more than 30 BIAs belonging to the 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline structural subclasses and displaying a predominant R-enantiomeric conformation have been isolated from N. nucifera, its BIA biosynthetic genes and enzymes remain unknown. Herein, we report the isolation and biochemical characterization of two O-methyltransferases (OMTs) involved in BIA biosynthesis in sacred lotus. Five homologous genes, designated NnOMT1-5 and encoding polypeptides sharing >40% amino acid sequence identity, were expressed in Escherichia coli Functional characterization of the purified recombinant proteins revealed that NnOMT1 is a regiospecific 1-benzylisoquinoline 6-O-methyltransferase (6OMT) accepting both R- and S-substrates, whereas NnOMT5 is mainly a 7-O-methyltransferase (7OMT), with relatively minor 6OMT activity and a strong stereospecific preference for S-enantiomers. Available aporphines were not accepted as substrates by either enzyme, suggesting that O-methylation precedes BIA formation from 1-benzylisoquinoline intermediates. Km values for NnOMT1 and NnOMT5 were 20 and 13 μm for (R,S)-norcoclaurine and (S)-N-methylcoclaurine, respectively, similar to those for OMTs from other BIA-producing plants. Organ-based correlations of alkaloid content, OMT activity in crude extracts, and OMT gene expression supported physiological roles for NnOMT1 and NnOMT5 in BIA metabolism, occurring primarily in young leaves and embryos of sacred lotus. In summary, our work identifies two OMTs involved in BIA metabolism in the medicinal plant N. nucifera.

Comprehensive Analysis and Functional Studies of WRKY Transcription Factors in Nelumbo nucifera

The WRKY family is one of the largest transcription factor (TF) families in plants and plays central roles in modulating plant stress responses and developmental processes, as well as secondary metabolic regulations. Lotus (Nelumbo nucifera) is an aquatic crop that has significant food, ornamental and pharmacological values. Here, we performed an overview analysis of WRKY TF family members in lotus, and studied their functions in environmental adaptation and regulation of lotus benzylisoquinoline alkaloid (BIA) biosynthesis. A total of 65 WRKY genes were identified in the lotus genome and they were well clustered in a similar pattern with their Arabidopsis homologs in seven groups (designated I, IIa-IIe, and III), although no lotus WRKY was clustered in the group IIIa. Most lotus WRKYs were functionally paired, which was attributed to the recently occurred whole genome duplication in lotus. In addition, lotus WRKYs were regulated dramatically by salicilic acid (SA), jasmonic acid (JA), and submergence treatments, and two lotus WRKYs, NnWRKY40a and NnWRKY40b, were significantly induced by JA and promoted lotus BIA biosynthesis through activating BIA biosynthetic genes. The investigation of WRKY TFs for this basal eudicot reveals new insights into the evolution of the WRKY family, and provides fundamental information for their functional studies and lotus breeding.

Structure-function studies of tetrahydroprotoberberine N-methyltransferase reveal the molecular basis of stereoselective substrate recognition

Benzylisoquinoline alkaloids (BIAs) are a structurally diverse class of plant-specialized metabolites that have been particularly well-studied in the order Ranunculales. The N-methyltransferases (NMTs) in BIA biosynthesis can be divided into three groups according to substrate specificity and amino acid sequence. Here, we report the first crystal structures of enzyme complexes from the tetrahydroprotoberberine NMT (TNMT) subclass, specifically for GfTNMT from the yellow horned poppy (Glaucium flavum). GfTNMT was co-crystallized with the cofactor S-adenosyl-l-methionine (d _min = 1.6 Å), the product S-adenosyl-l-homocysteine (d _min = 1.8 Å), or in complex with S-adenosyl-l-homocysteine and (S)-cis-N-methylstylopine (d _min = 1.8 Å). These structures reveal for the first time how a mostly hydrophobic L-shaped substrate recognition pocket selects for the (S)-cis configuration of the two central six-membered rings in protoberberine BIA compounds. Mutagenesis studies confirm and functionally define the roles of several highly-conserved residues within and near the GfTNMT-active site. The substrate specificity of TNMT enzymes appears to arise from the arrangement of subgroup-specific stereospecific recognition elements relative to catalytic elements that are more widely-conserved among all BIA NMTs. The binding mode of protoberberine compounds to GfTNMT appears to be similar to coclaurine NMT, with the isoquinoline rings buried deepest in the binding pocket. This binding mode differs from that of pavine NMT, in which the benzyl ring is bound more deeply than the isoquinoline rings. The insights into substrate recognition and catalysis provided here form a sound basis for the rational engineering of NMT enzymes for chemoenzymatic synthesis and metabolic engineering.

Endophytic Consortium With Diverse Gene-Regulating Capabilities of Benzylisoquinoline Alkaloids Biosynthetic Pathway Can Enhance Endogenous Morphine Biosynthesis in Papaver somniferum

Secondary metabolite biosynthesis in medicinal plants is multi-step cascade known to be modulated by associated endophytes. While a single endophyte is not able to upregulate all biosynthetic steps, limiting maximum yield achievement. Therefore to compliment the deficient characteristics in an endophyte we tried consortium of endophytes to achieve maximum yield. Here, efforts were made to maximize the in planta morphine yield, using consortium of two endophytes; SM1B (Acinetobacter sp.) upregulating most of the genes of morphine biosynthesis except T6ODM and CODM, and SM3B (Marmoricola sp.) upregulating T6ODM and CODM in alkaloid-less Papaver somniferum cv. Sujata. Consortium-inoculation significantly increased morphine and thebaine content, and also increased the photosynthetic efficiency of poppy plants resulted in increased biomass, capsule weight, and seed yields compared to single-inoculation. The increment in morphine content was due to the modulation of metabolic-flow of key intermediates including reticuline and thebaine, via upregulating pertinent biosynthetic genes and enhanced expression of COR, key gene for morphine biosynthesis. This is the first report demonstrating the endophytic-consortium complimenting the functional deficiency of one endophyte by another for upregulating multiple genes of a metabolic pathway similar to transgenics (overexpressing multiple genes) for obtaining enhanced yield of pharmaceutically important metabolites.

Benzylisoquinoline Alkaloids Biosynthesis in Sacred Lotus

Sacred lotus (Nelumbo nucifera Gaertn.) is an ancient aquatic plant used throughout Asia for its nutritional and medicinal properties. Benzylisoquinoline alkaloids (BIAs), mostly within the aporphine and bisbenzylisoquinoline structural categories, are among the main bioactive constituents in the plant. The alkaloids of sacred lotus exhibit promising anti-cancer, anti-arrhythmic, anti-HIV, and anti-malarial properties. Despite their pharmacological significance, BIA metabolism in this non-model plant has not been extensively investigated. In this review, we examine the diversity of BIAs in sacred lotus, with an emphasis on the distinctive stereochemistry of alkaloids found in this species. Additionally, we discuss our current understanding of the biosynthetic genes and enzymes involved in the formation of 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline alkaloids in the plant. We conclude that a comprehensive functional characterization of alkaloid biosynthetic enzymes using both in vitro and in vivo methods is required to advance our limited knowledge of BIA metabolism in the sacred lotus.

Complete biosynthesis of noscapine and halogenated alkaloids in yeast

Microbial biosynthesis of plant natural products from simple building blocks is a promising approach toward scalable production and modification of high-value compounds. The pathway for biosynthesis of noscapine, a potential anticancer compound, from canadine was recently elucidated as a 10-gene cluster from opium poppy. Here we demonstrate the de novo production of noscapine in Saccharomyces cerevisiae, through the reconstruction of a biosynthetic pathway comprising over 30 enzymes from plants, bacteria, mammals, and yeast itself, including 7 plant endoplasmic reticulum (ER)-localized enzymes. Optimization directed to tuning expression of pathway enzymes, host endogenous metabolic pathways, and fermentation conditions led to an over 18,000-fold improvement from initial noscapine titers to ∼2.2 mg/L. By feeding modified tyrosine derivatives to the optimized noscapine-producing strain we further demonstrated microbial production of halogenated benzylisoquinoline alkaloids. This work highlights the potential for microbial biosynthetic platforms to support the synthesis of valuable and novel alkaloid compounds, which can advance alkaloid-based drug discovery and development.

Green Routes for the Production of Enantiopure Benzylisoquinoline Alkaloids

Benzylisoquinoline alkaloids (BIAs) are among the most important plant secondary metabolites, in that they include a number of biologically active substances widely employed as pharmaceuticals. Isolation of BIAs from their natural sources is an expensive and time-consuming procedure as they accumulate in very low levels in plant. Moreover, total synthesis is challenging due to the presence of stereogenic centers. In view of these considerations, green and scalable methods for BIA synthesis using fully enzymatic approaches are getting more and more attention. The aim of this paper is to review fully enzymatic strategies for producing the benzylisoquinoline central precursor, (S)-norcoclaurine and its derivatives. Specifically, we will detail the current status of synthesis of BIAs in microbial hosts as well as using isolated and recombinant enzymes.

Mining Enzyme Diversity of Transcriptome Libraries through DNA Synthesis for Benzylisoquinoline Alkaloid Pathway Optimization in Yeast

The ever-increasing quantity of data deposited to GenBank is a valuable resource for mining new enzyme activities. Falling costs of DNA synthesis enables metabolic engineers to take advantage of this resource for identifying superior or novel enzymes for pathway optimization. Previously, we reported synthesis of the benzylisoquinoline alkaloid dihydrosanguinarine in yeast from norlaudanosoline at a molar conversion of 1.5%. Molar conversion could be improved by reduction of the side-product N-methylcheilanthifoline, a key bottleneck in dihydrosanguinarine biosynthesis. Two pathway enzymes, an N-methyltransferase and a cytochrome P450 of the CYP719A subfamily, were implicated in the synthesis of the side-product. Here, we conducted an extensive screen to identify enzyme homologues whose coexpression reduces side-product synthesis. Phylogenetic trees were generated from multiple sources of sequence data to identify a library of candidate enzymes that were purchased codon-optimized and precloned into expression vectors designed to facilitate high-throughput analysis of gene expression as well as activity assay. Simple in vivo assays were sufficient to guide the selection of superior enzyme homologues that ablated the synthesis of the side-product, and improved molar conversion of norlaudanosoline to dihydrosanguinarine to 10%.

Crystal structure of norcoclaurine-6-O-methyltransferase, a key rate-limiting step in the synthesis of benzylisoquinoline alkaloids

Growing pharmaceutical interest in benzylisoquinoline alkaloids (BIA) coupled with their chemical complexity make metabolic engineering of microbes to create alternative platforms of production an increasingly attractive proposition. However, precise knowledge of rate-limiting enzymes and negative feedback inhibition by end-products of BIA metabolism is of paramount importance for this emerging field of synthetic biology. In this work we report the structural characterization of (S)-norcoclaurine-6-O-methyltransferase (6OMT), a key rate-limiting step enzyme involved in the synthesis of reticuline, the final intermediate to be shared between the different end-products of BIA metabolism, such as morphine, papaverine, berberine and sanguinarine. Four different crystal structures of the enzyme from Thalictrum flavum (Tf 6OMT) were solved: the apoenzyme, the complex with S-adenosyl-l-homocysteine (SAH), the complexe with SAH and the substrate and the complex with SAH and a feedback inhibitor, sanguinarine. The Tf 6OMT structural study provides a molecular understanding of its substrate specificity, active site structure and reaction mechanism. This study also clarifies the inhibition of Tf 6OMT by previously suggested feedback inhibitors. It reveals its high and time-dependent sensitivity toward sanguinarine.