Stereochemical inversion of (S)-reticuline by a cytochrome P450 fusion in opium poppy

Structural diversity, evolutionary origin, and metabolic engineering of plant specialized benzylisoquinoline alkaloids

Covering: up to June 2024Benzylisoquinoline alkaloids (BIAs) represent a diverse class of plant specialized metabolites derived from L-tyrosine, exhibiting significant pharmacological properties such as anti-microbial, anti-spasmodic, anti-cancer, cardiovascular protection, and analgesic effects. The industrial production of valuable BIAs relies on extraction from plants; however, challenges concerning their low concentration and efficiency hinder drug development. Hence, alternative approaches, including biosynthesis and chemoenzymatic synthesis, have been explored. Model species like Papaver somniferum and Coptis japonica have played a key role in unraveling the biosynthetic pathways of BIAs; however, many aspects, particularly modified steps like oxidation and methylation, remain unclear. Critical enzymes, e.g., CYP450s and methyltransferases, play a substantial role in BIA backbone formation and modification, which is essential for understanding the origin and adaptive evolution of these plant specialized metabolites. This review comprehensively analyzes the structural diversity of reported BIAs and their distribution in plant lineages. In addition, the progress in understanding biosynthesis, evolution, and catalytic mechanisms underlying BIA biosynthesis is summarized. Finally, we discuss the progress and challenges in metabolic engineering, providing valuable insights into BIA drug development and the sustainable utilization of BIA-producing plants.

Two ubiquitous aldo-keto reductases in the genus Papaver support a patchwork model for morphine pathway evolution

The evolution of morphinan alkaloid biosynthesis in plants of the genus Papaver includes permutation of several processes including gene duplication, fusion, neofunctionalization, and deletion resulting in the present chemotaxonomy. A critical gene fusion event resulting in the key bifunctional enzyme reticuline epimerase (REPI), which catalyzes the stereochemical inversion of (S)-reticuline, was suggested to precede neofunctionalization of downstream enzymes leading to morphine biosynthesis in opium poppy (Papaver somniferum). The ancestrally related aldo-keto reductases 1,2-dehydroreticuline reductase (DRR), which occurs in some species as a component of REPI, and codeinone reductase (COR) catalyze the second and penultimate steps, respectively, in the pathway converting (S)-reticuline to morphine. Orthologs for each enzyme isolated from the transcriptomes of 12 Papaver species were shown to catalyze their respective reactions in species that capture states of the metabolic pathway prior to key evolutionary events, including the gene fusion event leading to REPI, thus suggesting a patchwork model for pathway evolution. Analysis of the structure and substrate preferences of DRR orthologs in comparison with COR orthologs revealed structure-function relationships underpinning the functional latency of DRR and COR orthologs in the genus Papaver, thus providing insights into the molecular events leading to the evolution of the pathway.

Mining and characterization of a novel cytochrome P450 MaCYP71BG22 involved in the C4-stereoselective hydroxylation of 1-deoxynojirimycin biosynthesis in mulberry leaves

1-Deoxynojirimycin (DNJ), a primary active component in mulberry leaves, has garnered significant attention due to its unique structure and notable pharmacological properties. Our previous investigations have elucidated the biosynthetic pathways of DNJ from lysine to 2-methylpiperidine. However, the hydroxylation process and its underlying mechanisms remain elusive. In this study, five CYP450s hydroxylase genes significantly correlated (P < 0.05) with DNJ content in mulberry leaves at various time were screened through transcriptome profile. MaCYP71BG22 was first cloned and functionally characterized. This gene was shown to specifically catalyze the stereoselective hydroxylation of (R)-2-methylpiperidine at the C4-position to produce (2R, 4R)-2-methylpiperidin-4-ol. In hairy roots of mulberry, overexpression of MaCYP71BG22 increased DNJ accumulation, while virus-induced gene silencing (VIGS) decreased its production. Furthermore, structural-function analysis pinpointed a critical residue, G460, in MaCYP71BG22, mutation of this residue to G460E enhanced the enzyme's catalytic efficiency. This study represents the first report of a CYP450 hydroxylase involved in the biosynthesis of piperidine alkaloids in mulberry leaves, and demonstrates that MaCYP71BG22 selectively catalyzes the C4-stereoselective hydroxylation of (R)-2-methylpiperidine in DNJ biosynthesis. These findings further elucidate the DNJ biosynthetic pathway and provide new insights into the stereo- and regio-selective hydroxylation abilities of CYP450s hydroxylase in DNJ biosynthesis.

Biosynthesis of the α-D-Mannosidase Inhibitor (-)-Swainsonine

(-)-Swainsonine is a polyhydroxylated indolizidine alkaloid with potent inhibitory activity against α-D-mannosidases. In this work, we successfully reconstituted swainsonine biosynthetic pathway both in vivo and in vitro. Our study unveiled a surprising epimerization mechanism involving an imine reductase (SwnN) and two non-heme iron and α-ketoglutarate-dependent oxygenases (SwnH2 and SwnH1). SwnH2 is a multifunctional enzyme responsible for both C2-hydroxylation and amine desaturation, while SwnN completes the oxidation-reduction sequence to achieve the net redox neutral epimerization. Notably, SwnN exhibits substrate-dependent stereospecificity and the stereochemical outcome of SwnN-catalyzed iminium reduction is determined by SwnH1-catalyzed C8-hydroxylation. We also discovered that an O -acetyl ester can serve as a detachable protecting/directing group, altering the site-selectivity of SwnH2-catalyzed hydroxylation while maintaining the stereoselectivity. Insights gained from the biochemical characterization of these tailoring enzymes enabled biocatalytic synthesis of a new polyhydroxylated indolizidine alkaloid, opening doors to the biosynthesis of diverse natural product-based glycosidase inhibitors.

Characterization of two CYP80 enzymes provides insights into aporphine alkaloid skeleton formation in Aristolochia contorta

Aporphine alkaloids are a large group of natural compounds with extensive pharmaceutical application prospects. The biosynthesis of aporphine alkaloids has been paid attentions in the past decades. Here, we determined the contents of four 1-benzylisoquinoline alkaloids and five aporphine alkaloids in root, stem, leaf, and flower of Aristolochia contorta Bunge, which belongs to magnoliids. Two CYP80 enzymes were identified and characterized from A. contorta. Both of them catalyze the unusual C-C phenol coupling reactions and directly form the aporphine alkaloid skeleton. AcCYP80G7 catalyzed the formation of hexacyclic aporphine corytuberine. AcCYP80Q8 catalyzed the formation of pentacyclic proaporphine glaziovine. Kingdom-wide phylogenetic analysis of the CYP80 family suggested that CYP80 first appeared in Nymphaeales. The functional divergence of hydroxylation and C-C (or C-O) phenol coupling preceded the divergence of magnoliids and eudicots. Probable crucial residues of AcCYP80Q8 were selected through sequence alignment and molecular docking. Site-directed mutagenesis revealed two crucial residues E284 and Y106 for the catalytic reaction. Identification and characterization of two aporphine skeleton-forming enzymes provide insights into the biosynthesis of aporphine alkaloids.

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.

Promising approaches for simultaneous enhancement of medicinally significant benzylisoquinoline alkaloids in opium poppy

Benzylisoquinoline alkaloids (BIAs) produced in opium poppy have been evidenced to heal patients suffering from various diseases. They, therefore, hold an integral position in the herbal drug industry. Despite the adoption of several approaches for the large-scale production of BIAs, opium poppy remains the only platform in this purpose. The only disadvantage associated with producing BIAs in the plant is their small quantity. Thus, recruiting strategies that boost their levels is deemed necessary. All the methods which have been employed so far are just able to enhance a maximum of two BIAs. Thus, if these methods are utilized, a sizable amount of time and budget must be spent on the synthesis of all BIAs. Hence, the exploitation of strategies which increase the content of all BIAs at the same time is more commercially effective and time-saving, avoiding the laborious step of resolving the biosynthetic pathway of each compound. Exposure to biotic and abiotic elicitors, development of a synthetic auto-tetraploid, overexpression of a WRKY transcription factor, formation of an artificial metabolon, and suppression of a gene in the shikimate pathway and miRNA are strategies that turn opium poppy into a versatile bioreactor for the concurrent and massive production of BIAs. The last three strategies have never been applied for BIA biosynthetic pathways.

Redox Out of the Box: Catalytic Versatility Across NAD(P)H-Dependent Oxidoreductases

The asymmetric reduction of double bonds using NAD(P)H-dependent oxidoreductases has proven to be an efficient tool for the synthesis of important chiral molecules in research and on industrial scale. These enzymes are commercially available in screening kits for the reduction of C=O (ketones), C=C (activated alkenes), or C=N bonds (imines). Recent reports, however, indicate that the ability to accommodate multiple reductase activities on distinct C=X bonds occurs in different enzyme classes, either natively or after mutagenesis. This challenges the common perception of highly selective oxidoreductases for one type of electrophilic substrate. Consideration of this underexplored potential in enzyme screenings and protein engineering campaigns may contribute to the identification of complementary biocatalytic processes for the synthesis of chiral compounds. This review will contribute to a global understanding of the promiscuous behavior of NAD(P)H-dependent oxidoreductases on C=X bond reduction and inspire future discoveries with respect to unconventional biocatalytic routes in asymmetric synthesis.

Regulation of T16H subcellular localization for promoting its catalytic efficiency in yeast cells

To investigate the effect of subcellular localization on the transformation efficiency of heterologous expressed functional P450s in yeast. Microbial biotransformation offers a promising substitute for the direct extraction of natural products, but its viability in industrial applications depends on achieving high transformation efficiencies. To investigate the influence of subcellular microenvironments on the activity of heterologously expressed P450s, Catharanthus roseus tabersonine 16-hydroxylase (T16H) was chosen, and its subcellular localization was regulated by fusing organelle-localization signals. Interestingly, this manipulation had no effect on the gene expression levels of T16H, but resulted in varying conversion rates from tabersonine to 16-hydroxy tabersonine. Notably, the highest transformation efficiency was observed in yeast cells expressing peroxisome-localized T16H. Given the alkaline pH optimum for P450s, the alkaline peroxisomal lumen could be a suitable compartment for P450s reactions to achieve high transformation efficiency using yeast cells. Different organelle-localization of T16H in yeast cells resulted in varying conversion rates, suggesting that compartmentalizing the expression of target enzymes could be a viable approach to increase transformation efficiency in yeast.

Proposal for the classification of sinomenine alkaloids

The chemical structure of sinoacutine is formed by a phenanthrene nucleus and an ethylamine bridge. Because it has a similar parent structure to morphine, it is subdivided into morphinane. At present, all reports have pointed out that the basic skeleton of morphine alkaloids is salutaridine (the isomer of sinoacutine), which is generated by the phenol coupling reaction of (R)-reticuline. This study shows that the biosynthetic precursors of sinoacutine and salutaridine are different. In this paper, the sinoacutine synthetase (SinSyn) gene was cloned from Sinomenium acutum and expressed SinSyn protein. Sinoacutine was produced by SinSyn catalyzed (S)-reticuline, according to the results of enzyme-catalyzed experiments. The optical activity, nuclear magnetic resonance, and mass spectrum of sinoacutine and salutaridine were analyzed. The classification and pharmacological action of isoquinoline alkaloids were discussed. It was suggested that sinoacutine should be separated from morphinane and classified as sinomenine alkaloids.

Structural Characterization and Molecular Dynamics Study of the REPI Fusion Protein from Papaver somniferum L

REPI is a pivotal point enzyme in plant benzylisoquinoline alkaloid metabolism as it promotes the evolution of the biosynthetic branch of morphinan alkaloids. Experimental studies of its activity led to the identification of two modules (DRS and DRR) that catalyze two sequential steps of the epimerization of (S)- to (R)-reticuline. Recently, special attention has been paid to its genetic characterization and evolutionary history, but no structural analyses of the REPI protein have been conducted to date. We present here a computational structural characterization of REPI with heme and NADP cofactors in the apo state and in three complexes with substrate (S)-reticuline in DRS and intermediate 1,2-dehydroreticuline in DRS and in DRR. Since no experimental structure exists for REPI, we used its AlphaFold model as a scaffold to build up these four systems, which were submitted to all-atom molecular dynamics (MD) simulations. A comparison of MD results for the four systems revealed key dynamic changes associated with cofactor and ligand binding and provided a dynamic picture of the evolution of their structures and interactions. We also explored the possible dynamic occurrence of tunnels and electrostatic highways potentially involved in alternative mechanisms for channeling the intermediate from DRS to DRR.

Engineering of CYP82Y1, a cytochrome P450 monooxygenase: a key enzyme in noscapine biosynthesis in opium poppy

Protein engineering provides a powerful base for the circumvention of challenges tied with characteristics accountable for enzyme functions. CYP82Y1 introduces a hydroxyl group (-OH) into C1 of N-methylcanadine as the substrate to yield 1-hydroxy-N-methylcanadine. This chemical process has been found to be the gateway to noscapine biosynthesis. Owning to the importance of CYP82Y1 in this biosynthetic pathway, it has been selected as a target for enzyme engineering. The insertion of tags to the N- and C-terminal of CYP82Y1 was assessed for their efficiencies for improvement of the physiological performances of CYP82Y1. Although these attempts achieved some positive results, further strategies are required to dramatically enhance the CYP82Y1 activity. Here methods that have been adopted to achieve a functionally improved CYP82Y1 will be reviewed. In addition, the possibility of recruitment of other techniques having not yet been implemented in CYP82Y1 engineering, including the substitution of the residues located in the substrate recognition site, formation of the synthetic fusion proteins, and construction of the artificial lipid-based scaffold will be discussed. Given the fact that the pace of noscapine synthesis is constrained by the CYP82Y1-catalyzing step, the methods proposed here are capable of accelerating the rate of reaction performed by CYP82Y1 through improving its properties, resulting in the enhancement of noscapine accumulation.

Elucidation of the mescaline biosynthetic pathway in peyote (Lophophora williamsii)

Peyote (Lophophora williamsii) is an entheogenic and medicinal cactus native to the Chihuahuan desert. The psychoactive and hallucinogenic properties of peyote are principally attributed to the phenethylamine derivative mescaline. Despite the isolation of mescaline from peyote over 120 years ago, the biosynthetic pathway in the plant has remained undiscovered. Here, we use a transcriptomics and homology-guided gene discovery strategy to elucidate a near-complete biosynthetic pathway from l-tyrosine to mescaline. We identified a cytochrome P450 that catalyzes the 3-hydroxylation of l-tyrosine to l-DOPA, a tyrosine/DOPA decarboxylase yielding dopamine, and four substrate-specific and regiospecific substituted phenethylamine O-methyltransferases. Biochemical assays with recombinant enzymes or functional analyses performed by feeding putative precursors to engineered yeast (Saccharomyces cerevisiae) strains expressing candidate peyote biosynthetic genes were used to determine substrate specificity, which served as the basis for pathway elucidation. Additionally, an N-methyltransferase displaying broad substrate specificity and leading to the production of N-methylated phenethylamine derivatives was identified, which could also function as an early step in the biosynthesis of tetrahydroisoquinoline alkaloids in peyote.

Concise synthesis of (R)-reticuline and (+)-salutaridine by combining early-stage organic synthesis and late-stage biocatalysis

Efficient access to the morphinan scaffold remains a major challenge in both synthetic chemistry and biotechnology. Here, a biomimetic chemo-enzymatic strategy to synthesize the natural promorphinan intermediate (+)-salutaridine is demonstrated. By combining early-stage organic synthesis with enzymatic asymmetric key step transformations, the prochiral natural intermediate 1,2-dehydroreticuline was prepared and subsequently stereoselectively reduced by the enzyme 1,2-dehydroreticuline reductase obtaining (R)-reticuline in high ee and yield (>99% ee, up to quant. conversion, 92% isol. yield). In the final step, membrane-bound salutaridine synthase was used to perform the selective ortho-para phenol coupling to give (+)-salutaridine. The synthetic route shows the potential of combining early-stage advanced organic chemistry to minimize protecting group techniques with late-stage multi-step biocatalysis to provide an unprecedented access to the medicinally important compound class of promorphinans.

Biotechnological Approaches for Enhancing Polyhydroxyalkanoates (PHAs) Production: Current and Future Perspectives

The benefits of biotechnology are not limited to genetic engineering, but it also displays its great impact on industrial uses of crops (e.g., biodegradable plastics). Polyhydroxyalkanoates (PHAs) make a diverse class of bio-based and biodegradable polymers naturally synthesized by numerous microorganisms. However, several C3 and C4 plants have also been genetically engineered to produce PHAs. The highest production yield of PHAs was obtained with a well-known C3 plant, Arabidopsis thaliana, upto 40% of the dry weight of the leaf. This review summarizes all biotechnological mechanisms that have been adopted with the goal of increasing PHAs production in bacteria and plant species alike. Moreover, the possibility of using some methods that have not been applied in bioplastic science are discussed with special attention to plants. These include producing PHAs in transgenic hairy roots and cell suspension cultures, making transformed bacteria and plants via transposons, constructing an engineered metabolon, and overexpressing of phaP and the ABC operon concurrently. Taken together, that biotechnology will be highly beneficial for reducing plastic pollution through the implementation of biotechnological strategies is taken for granted.

Pathway elucidation and microbial synthesis of proaporphine and bis-benzylisoquinoline alkaloids from sacred lotus (Nelumbo nucifera)

Sacred lotus (Nelumbo nucifera) has been utilized as a food, medicine, and spiritual symbol for nearly 3000 years. The medicinal properties of lotus are largely attributed to its unique profile of benzylisoquinoline alkaloids (BIAs), which includes potential anti-cancer, anti-malarial and anti-arrhythmic compounds. BIA biosynthesis in sacred lotus differs markedly from that of opium poppy and other members of the Ranunculales, most notably in an abundance of BIAs possessing the (R)-stereochemical configuration and the absence of reticuline, a major branchpoint intermediate in most BIA producers. Owing to these unique metabolic features and the pharmacological potential of lotus, we set out to elucidate the BIA biosynthesis network in N. nucifera. Here we show that lotus CYP80G (NnCYP80G) and a superior ortholog from Peruvian nutmeg (Laurelia sempervirens; LsCYP80G) stereospecifically convert (R)-N-methylcoclaurine to the proaporphine alkaloid glaziovine, which is subsequently methylated to pronuciferine, the presumed precursor to nuciferine. While sacred lotus employs a dedicated (R)-route to aporphine alkaloids from (R)-norcoclaurine, we implemented an artificial stereochemical inversion approach to flip the stereochemistry of the core BIA pathway. Exploiting the unique substrate specificity of dehydroreticuline synthase from common poppy (Papaver rhoeas) and pairing it with dehydroreticuline reductase enabled de novo synthesis of (R)-N-methylcoclaurine from (S)-norcoclaurine and its subsequent conversion to pronuciferine. We leveraged our stereochemical inversion approach to also elucidate the role of NnCYP80A in sacred lotus metabolism, which we show catalyzes the stereospecific formation of the bis-BIA nelumboferine. Screening our collection of 66 plant O-methyltransferases enabled conversion of nelumboferine to liensinine, a potential anti-cancer bis-BIA from sacred lotus. Our work highlights the unique benzylisoquinoline metabolism of N. nucifera and enables the targeted overproduction of potential lotus pharmaceuticals using engineered microbial systems.

Elucidation of the (R)-enantiospecific benzylisoquinoline alkaloid biosynthetic pathways in sacred lotus (Nelumbo nucifera)

Benzylisoquinoline alkaloids (BIAs) are a structurally diverse group of plant specialized metabolites found mainly in members of the order Ranunculales, including opium poppy (Papaver somniferum), for which BIA biosynthetic pathways leading to the critical drugs morphine, noscapine, and sanguinarine have been elucidated. Sacred lotus (Nelumbo nucifera), in the order Proteales, accumulates medicinal BIAs in the proaporphine, aporphine, and bisbenzylisoquinoline structural subgroups with a prevalence of R enantiomers, opposed to the dominant S configuration occurring in the Ranunculales. Nevertheless, distinctive BIA biosynthetic routes in sacred lotus have not been explored. In planta labeling experiments and in vitro assays with recombinant enzymes and plant protein extracts showed that dopamine and 4-hydroxyphenylacetaldehyde derived from L-tyrosine serve as precursors for the formation of (R,S)-norcoclaurine in sacred lotus, whereas only (R)-norcoclaurine byproducts are favored in the plant by action of R-enantiospecific methyltransferases and cytochrome P450 oxidoreductases (CYPs). Enzymes responsible for the R-enantiospecific formation of proaporphine (NnCYP80Q1) and bisbenzylisoquinoline (NnCYP80Q2) scaffolds, and a methylenedioxy bridge introduction on aporphine substrates (NnCYP719A22) were identified, whereas additional aspects of the biosynthetic pathways leading to the distinctive alkaloid profile are discussed. This work expands the availability of molecular tools that can be deployed in synthetic biology platforms for the production of high-value alkaloids.

Strong Feedback Inhibition of Key Enzymes in the Morphine Biosynthetic Pathway from Opium Poppy Detectable in Engineered Yeast

Systematic screening of morphine pathway intermediates in engineered yeast revealed key biosynthetic enzymes displaying potent feedback inhibition: 3'-hydroxy-N-methylcoclaurine 4'-methyltransferase (4'OMT), which yields (S)-reticuline, and the coupled salutaridinol-7-O-acetyltransferase (SalAT) and thebaine synthase (THS2) enzyme system that produces thebaine. The addition of deuterated reticuline-d1 to a yeast strain able to convert (S)-norcoclaurine to (S)-reticuline showed reduced product accumulation in response to the feeding of all four successive pathway intermediates. Similarly, the addition of deuterated thebaine-d3 to a yeast strain able to convert salutaridine to thebaine showed reduced product accumulation from exogenous salutaridine or salutaridinol. In vitro analysis showed that reticuline is a noncompetitive inhibitor of 4'OMT, whereas thebaine exerts mixed inhibition on SalAT/THS2. In a yeast strain capable of de novo morphine biosynthesis, the addition of reticuline and thebaine resulted in the accumulation of several pathway intermediates. In contrast, morphine had no effect, suggesting that circumventing the interaction of reticuline and thebaine with 4'OMT and SalAT/THS2, respectively, could substantially increase opiate alkaloid titers in engineered yeast.

The Current Developments in Medicinal Plant Genomics Enabled the Diversification of Secondary Metabolites' Biosynthesis

Medicinal plants produce important substrates for their adaptation and defenses against environmental factors and, at the same time, are used for traditional medicine and industrial additives. Plants have relatively little in the way of secondary metabolites via biosynthesis. Recently, the whole-genome sequencing of medicinal plants and the identification of secondary metabolite production were revolutionized by the rapid development and cheap cost of sequencing technology. Advances in functional genomics, such as transcriptomics, proteomics, and metabolomics, pave the way for discoveries in secondary metabolites and related key genes. The multi-omics approaches can offer tremendous insight into the variety, distribution, and development of biosynthetic gene clusters (BGCs). Although many reviews have reported on the plant and medicinal plant genome, chemistry, and pharmacology, there is no review giving a comprehensive report about the medicinal plant genome and multi-omics approaches to study the biosynthesis pathway of secondary metabolites. Here, we introduce the medicinal plant genome and the application of multi-omics tools for identifying genes related to the biosynthesis pathway of secondary metabolites. Moreover, we explore comparative genomics and polyploidy for gene family analysis in medicinal plants. This study promotes medicinal plant genomics, which contributes to the biosynthesis and screening of plant substrates and plant-based drugs and prompts the research efficiency of traditional medicine.

Engineering medicinal plant-derived CYPs: a promising strategy for production of high-valued secondary metabolites

Cytochorme P450s (CYPs) play a critical role in the catalysis of secondary metabolite biosynthetic pathways. For their commercial use, various strategies for metabolic pathway engineering using CYP as a potential target have been explored. Plants produce a vast diversity of secondary metabolites which are being used to treat various ailments and diseases. Some of these metabolites are difficult to obtain in large quantities limiting their industrial use. Cytochrome P450 enzymes (CYPs) are important catalysts in the biosynthesis of highly valued secondary metabolites, and are found in all domains of life. With the development of high-throughput sequencing and high-resolution mass spectrometry, new biosynthetic pathways and associated CYPs are being identified. In this review, we present CYPs identified from medicinal plants as a potential game changer in the metabolic engineering of secondary metabolic pathways. We present the achievements made so far in enhancing the production of important bioactivities through pathway engineering, giving some popular examples. At last, current challenges and possible strategies to overcome the limitations associated with CYP engineering to enhance the biosynthesis of target secondary metabolites are also highlighted.

Plant biosynthetic gene clusters in the context of metabolic evolution

Covering: up to 2022Plants produce a wide range of structurally and biosynthetically diverse natural products to interact with their environment. These specialised metabolites typically evolve in limited taxonomic groups presumably in response to specific selective pressures. With the increasing availability of sequencing data, it has become apparent that in many cases the genes encoding biosynthetic enzymes for specialised metabolic pathways are not randomly distributed on the genome. Instead they are physically linked in structures such as arrays, pairs and clusters. The exact function of these clusters is debated. In this review we take a broad view of gene arrangement in plant specialised metabolism, examining types of structures and variation. We discuss the evolution of biosynthetic gene clusters in the wider context of metabolism, populations and epigenetics. Finally, we synthesise our observations to propose a new hypothesis for biosynthetic gene cluster formation in plants.

A functionally conserved STORR gene fusion in Papaver species that diverged 16.8 million years ago

The STORR gene fusion event is considered essential for the evolution of the promorphinan/morphinan subclass of benzylisoquinoline alkaloids (BIAs) in opium poppy as the resulting bi-modular protein performs the isomerization of (S)- to (R)-reticuline essential for their biosynthesis. Here, we show that of the 12 Papaver species analysed those containing the STORR gene fusion also contain promorphinans/morphinans with one important exception. P. californicum encodes a functionally conserved STORR but does not produce promorphinans/morphinans. We also show that the gene fusion event occurred only once, between 16.8-24.1 million years ago before the separation of P. californicum from other Clade 2 Papaver species. The most abundant BIA in P. californicum is (R)-glaucine, a member of the aporphine subclass of BIAs, raising the possibility that STORR, once evolved, contributes to the biosynthesis of more than just the promorphinan/morphinan subclass of BIAs in the Papaveraceae.

Phloem-specific localization of benzylisoquinoline alkaloid metabolism in opium poppy

Opium poppy is the only commercial source of the narcotic analgesics morphine and codeine, and semi-synthetic derivatives of the natural opiate precursor thebaine, including oxycodone and the opioid antagonist naloxone. The plant also accumulates the vasodilator and antitussive agents papaverine and noscapine, respectively, which together with morphine, codeine and thebaine comprise the major benzylisoquinoline alkaloids (BIAs) in opium poppy. A majority of enzymes involved in the highly branched BIA metabolism in opium poppy have now been discovered, with many specifically localized to sieve elements of the phloem based on immunofluorescence labeling techniques. Transcripts corresponding to sieve element-localized biosynthetic enzymes were detected in companion cells, as expected. The more recent application of shotgun proteomics has shown that several enzymes operating late in the morphine and noscapine biosynthetic pathways occur primarily in laticifers that are adjacent or proximal to sieve elements. BIA biosynthesis and accumulation in opium poppy involves three phloem cell types and implicates the translocation of key pathway intermediates between sieve elements and laticifers. The recent isolation of uptake transporters associated with laticifers supports an apoplastic rather than a symplastic route for translocation. In spite of the extensive elucidation of BIA biosynthetic enzymes in opium poppy, additional transporters and other auxiliary proteins are clearly necessary to support the complex spatial organization and dynamics involved in product formation and sequestration. In this review, we provide an update of BIA metabolism in opium poppy with a focus on the role of phloem in the biosynthesis of the major alkaloids.

Compartmentalization at the interface of primary and alkaloid metabolism

Plants produce many compounds used by humans as medicines, including alkaloids of the benzylisoquinoline (BIA), monoterpene indole (MIA) and tropane classes. The biosynthetic pathways of these pharmaceutical alkaloids are complex and spatially segregated across several tissues, cell-types and organelles. This review discusses the origin of primary metabolic inputs required by these specialized biosynthetic pathways and considers aspects relevant to their spatial organization. These factors are important for alkaloid production both in the native plants and for synthetic biology pathway reconstruction in microorganisms.

Concise total synthesis of opioids

Morphine and related alkaloids are among the most representative natural medicines that have benefited human beings for over two centuries. Industrial manufacturing of these therapeutically valuable and structurally fascinating molecules...

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.

Three chromosome-scale Papaver genomes reveal punctuated patchwork evolution of the morphinan and noscapine biosynthesis pathway

For millions of years, plants evolve plenty of structurally diverse secondary metabolites (SM) to support their sessile lifestyles through continuous biochemical pathway innovation. While new genes commonly drive the evolution of plant SM pathway, how a full biosynthetic pathway evolves remains poorly understood. The evolution of pathway involves recruiting new genes along the reaction cascade forwardly, backwardly, or in a patchwork manner. With three chromosome-scale Papaver genome assemblies, we here reveal whole-genome duplications (WGDs) apparently accelerate chromosomal rearrangements with a nonrandom distribution towards SM optimization. A burst of structural variants involving fusions, translocations and duplications within 7.7 million years have assembled nine genes into the benzylisoquinoline alkaloids gene cluster, following a punctuated patchwork model. Biosynthetic gene copies and their total expression matter to morphinan production. Our results demonstrate how new genes have been recruited from a WGD-induced repertoire of unregulated enzymes with promiscuous reactivities to innovate efficient metabolic pathways with spatiotemporal constraint.

Structural studies of codeinone reductase reveal novel insights into aldo-keto reductase function in benzylisoquinoline alkaloid biosynthesis

Benzylisoquinoline alkaloids (BIAs) are a class of specialized metabolites with a diverse range of chemical structures and physiological effects. Codeine and morphine are two closely related BIAs with particularly useful analgesic properties. The aldo-keto reductase (AKR) codeinone reductase (COR) catalyzes the final and penultimate steps in the biosynthesis of codeine and morphine, respectively, in opium poppy (Papaver somniferum). However, the structural determinants that mediate substrate recognition and catalysis are not well defined. Here, we describe the crystal structure of apo-COR determined to a resolution of 2.4 Å by molecular replacement using chalcone reductase as a search model. Structural comparisons of COR to closely related plant AKRs and more distantly related homologues reveal a novel conformation in the β1α1 loop adjacent to the BIA-binding pocket. The proximity of this loop to several highly conserved active-site residues and the expected location of the nicotinamide ring of the NADP(H) cofactor suggest a model for BIA recognition that implies roles for several key residues. Using site-directed mutagenesis, we show that substitutions at Met-28 and His-120 of COR lead to changes in AKR activity for the major and minor substrates codeinone and neopinone, respectively. Our findings provide a framework for understanding the molecular basis of substrate recognition in COR and the closely related 1,2-dehydroreticuline reductase responsible for the second half of a stereochemical inversion that initiates the morphine biosynthesis pathway.

Evolution-aided engineering of plant specialized metabolism

The evolution of new traits in living organisms occurs via the processes of mutation, recombination, genetic drift, and selection. These processes that have resulted in the immense biological diversity on our planet are also being employed in metabolic engineering to optimize enzymes and pathways, create new-to-nature reactions, and synthesize complex natural products in heterologous systems. In this review, we discuss two evolution-aided strategies for metabolic engineering-directed evolution, which improves upon existing genetic templates using the evolutionary process, and combinatorial pathway reconstruction, which brings together genes evolved in different organisms into a single heterologous host. We discuss the general principles of these strategies, describe the technologies involved and the molecular traits they influence, provide examples of their use, and discuss the roadblocks that need to be addressed for their wider adoption. A better understanding of these strategies can provide an impetus to research on gene function discovery and biochemical evolution, which is foundational for improved metabolic engineering. These evolution-aided approaches thus have a substantial potential for improving our understanding of plant metabolism in general, for enhancing the production of plant metabolites, and in sustainable agriculture.

The role of biocatalysis in the asymmetric synthesis of alkaloids - an update

Alkaloids are a group of natural products with interesting pharmacological properties and a long history of medicinal application. Their complex molecular structures have fascinated chemists for decades, and their total synthesis still poses a considerable challenge. In a previous review, we have illustrated how biocatalysis can make valuable contributions to the asymmetric synthesis of alkaloids. The chemo-enzymatic strategies discussed therein have been further explored and improved in recent years, and advances in amine biocatalysis have vastly expanded the opportunities for incorporating enzymes into synthetic routes towards these important natural products. The present review summarises modern developments in chemo-enzymatic alkaloid synthesis since 2013, in which the biocatalytic transformations continue to take an increasingly 'central' role.

Recent trends in biocatalysis

Biocatalysis has undergone revolutionary progress in the past century. Benefited by the integration of multidisciplinary technologies, natural enzymatic reactions are constantly being explored. Protein engineering gives birth to robust biocatalysts that are widely used in industrial production. These research achievements have gradually constructed a network containing natural enzymatic synthesis pathways and artificially designed enzymatic cascades. Nowadays, the development of artificial intelligence, automation, and ultra-high-throughput technology provides infinite possibilities for the discovery of novel enzymes, enzymatic mechanisms and enzymatic cascades, and gradually complements the lack of remaining key steps in the pathway design of enzymatic total synthesis. Therefore, the research of biocatalysis is gradually moving towards the era of novel technology integration, intelligent manufacturing and enzymatic total synthesis.

Engineering Saccharomyces cerevisiae to produce plant benzylisoquinoline alkaloids

Benzylisoquinoline alkaloids (BIAs) are a diverse family of plant natural products with extensive pharmacological properties, but the yield of BIAs from plant is limited. The understanding of BIA biosynthetic mechanism in plant and the development of synthetic biology enable the possibility to produce BIAs through microbial fermentation, as an alternative to agriculture-based supply chains. In this review, we discussed the engineering strategies to synthesize BIAs in Saccharomyces cerevisiae (yeast) and improve BIA production level, including heterologous pathway reconstruction, enzyme engineering, expression regulation, host engineering and fermentation engineering. We also highlight recent metabolic engineering advances in the production of BIAs in yeast.

Cytochrome P450 Enzymes as Key Drivers of Alkaloid Chemical Diversification in Plants

Plants produce more than 20,000 nitrogen-containing heterocyclic metabolites called alkaloids. These chemicals serve numerous eco-physiological functions in the plants as well as medicines and psychedelic drugs for human for thousands of years, with the anti-cancer agent vinblastine and the painkiller morphine as the best-known examples. Cytochrome P450 monooxygenases (P450s) play a key role in generating the structural variety that underlies this functional diversity of alkaloids. Most alkaloid molecules are heavily oxygenated thanks to P450 enzymes' activities. Moreover, the formation and re-arrangement of alkaloid scaffolds such as ring formation, expansion, and breakage that contribute to their structural diversity and bioactivity are mainly catalyzed by P450s. The fast-expanding genomics and transcriptomics databases of plants have accelerated the investigation of alkaloid metabolism and many players behind the complexity and uniqueness of alkaloid biosynthetic pathways. Here we discuss recent discoveries of P450s involved in the chemical diversification of alkaloids and how these inform our approaches in understanding plant evolution and producing plant-derived drugs.

Biosynthesis and synthetic biology of psychoactive natural products

Psychoactive natural products play an integral role in the modern world. The tremendous structural complexity displayed by such molecules confers diverse biological activities of significant medicinal value and sociocultural impact. Accordingly, in the last two centuries, immense effort has been devoted towards establishing how plants, animals, and fungi synthesize complex natural products from simple metabolic precursors. The recent explosion of genomics data and molecular biology tools has enabled the identification of genes encoding proteins that catalyze individual biosynthetic steps. Once fully elucidated, the "biosynthetic pathways" are often comparable to organic syntheses in elegance and yield. Additionally, the discovery of biosynthetic enzymes provides powerful catalysts which may be repurposed for synthetic biology applications, or implemented with chemoenzymatic synthetic approaches. In this review, we discuss the progress that has been made toward biosynthetic pathway elucidation amongst four classes of psychoactive natural products: hallucinogens, stimulants, cannabinoids, and opioids. Compounds of diverse biosynthetic origin - terpene, amino acid, polyketide - are identified, and notable mechanisms of key scaffold transforming steps are highlighted. We also provide a description of subsequent applications of the biosynthetic machinery, with an emphasis placed on the synthetic biology and metabolic engineering strategies enabling heterologous production.

Diversity in Chemical Structures and Biological Properties of Plant Alkaloids

Phytochemicals belonging to the group of alkaloids are signature specialized metabolites endowed with countless biological activities. Plants are armored with these naturally produced nitrogenous compounds to combat numerous challenging environmental stress conditions. Traditional and modern healthcare systems have harnessed the potential of these organic compounds for the treatment of many ailments. Various chemical entities (functional groups) attached to the central moiety are responsible for their diverse range of biological properties. The development of the characterization of these plant metabolites and the enzymes involved in their biosynthesis is of an utmost priority to deliver enhanced advantages in terms of biological properties and productivity. Further, the incorporation of whole/partial metabolic pathways in the heterologous system and/or the overexpression of biosynthetic steps in homologous systems have both become alternative and lucrative methods over chemical synthesis in recent times. Moreover, in-depth research on alkaloid biosynthetic pathways has revealed numerous chemical modifications that occur during alkaloidal conversions. These chemical reactions involve glycosylation, acylation, reduction, oxidation, and methylation steps, and they are usually responsible for conferring the biological activities possessed by alkaloids. In this review, we aim to discuss the alkaloidal group of plant specialized metabolites and their brief classification covering major categories. We also emphasize the diversity in the basic structures of plant alkaloids arising through enzymatically catalyzed structural modifications in certain plant species, as well as their emerging diverse biological activities. The role of alkaloids in plant defense and their mechanisms of action are also briefly discussed. Moreover, the commercial utilization of plant alkaloids in the marketplace displaying various applications has been enumerated.

Minimizing the risk of deducing wrong natural product structures from NMR data

There continues to be a disturbing number of natural products reported in the literature whose structures are incorrect. At least in part, this reflects the fact that many natural product chemists have limited formal nuclear magnetic resonance training. Gaps in training and lack of awareness regarding the challenges and ambiguities associated with two-dimensional nuclear magnetic resonance data interpretation can easily lead to errors in structure elucidation. The purpose of this tutorial is to point out some of these issues, highlight the kinds of errors that have been made and provide specific advice on how to avoid these missteps such that the risk of reporting a wrong structure is minimized.

Benzylisoquinoline alkaloid analysis using high-resolution Orbitrap LC-MSn

Benzylisoquinoline alkaloids (BIAs) have profound implications on human health owing to their potent pharmacological properties. Notable naturally occurring BIAs are the narcotic analgesics morphine, the cough suppressant codeine, the potential anticancer drug noscapine, the muscle relaxant papaverine, and the antimicrobial sanguinarine, all of which are produced in opium poppy (Papaver somniferum). Thebaine, an intermediate in the biosynthesis of codeine and morphine, is used in the manufacture of semisynthetic opiates, including oxycodone and naloxone. As the only commercial source of pharmaceutical opiates, opium poppy has been the focus of considerable research to understand BIA metabolism in the plant. The elucidation of several BIA biosynthetic pathways has enabled the development of synthetic biology platforms aimed at the alternative commercial production of valuable phytochemicals in microorganisms. The detection and identification of BIA pathway products and intermediates in complex extracts is essential for the continuing advancement of research in plant specialized metabolism and microbial synthetic biology. Herein, we report the use of liquid chromatography coupled with linear trap quadrupole and high-resolution Orbitrap multistage mass spectrometry to characterize 44 authentic BIAs using collision-induced dissociation (CID), higher-energy collisional dissociation (HCD), and pulsed Q collision-induced dissociation (PQD) MS² fragmentation, with MS² CID followed by MS³ and MS⁴ fragmentation. Our deep library of diagnostic spectral data constitutes a valuable resource for BIAs identification. In addition, we identified 22 BIAs in opium poppy latex and roots extracts.

Streamlining Natural Products Biomanufacturing With Omics and Machine Learning Driven Microbial Engineering

Increasing demands for the supply of biopharmaceuticals have propelled the advancement of metabolic engineering and synthetic biology strategies for biomanufacturing of bioactive natural products. Using metabolically engineered microbes as the bioproduction hosts, a variety of natural products including terpenes, flavonoids, alkaloids, and cannabinoids have been synthesized through the construction and expression of known and newly found biosynthetic genes primarily from model and non-model plants. The employment of omics technology and machine learning (ML) platforms as high throughput analytical tools has been increasingly leveraged in promoting data-guided optimization of targeted biosynthetic pathways and enhancement of the microbial production capacity, thereby representing a critical debottlenecking approach in improving and streamlining natural products biomanufacturing. To this end, this mini review summarizes recent efforts that utilize omics platforms and ML tools in strain optimization and prototyping and discusses the beneficial uses of omics-enabled discovery of plant biosynthetic genes in the production of complex plant-based natural products by bioengineered microbes.

Back to the plant: overcoming roadblocks to the microbial production of pharmaceutically important plant natural products

Microbial fermentation platforms offer a cost-effective and sustainable alternative to plant cultivation and chemical synthesis for the production of many plant-derived pharmaceuticals. Plant alkaloids, particularly benzylisoquinoline alkaloids and monoterpene indole alkaloids, and recently cannabinoids have become attractive targets for microbial biosynthesis owing to their medicinal importance. Recent advances in the discovery of pathway components, together with the application of synthetic biology tools, have facilitated the assembly of plant alkaloid and cannabinoid pathways in the microbial hosts Escherichia coli and Saccharomyces cerevisiae. This review highlights key aspects of these pathways in the framework of overcoming bottlenecks in microbial production to further improve end-product titers. We discuss the opportunities that emerge from a better understanding of the pathway components by further study of the plant, and strategies for generation of new and advanced medicinal compounds.

Protein Engineering for Improving and Diversifying Natural Product Biosynthesis

Proteins found in nature have traditionally been the most frequently used biocatalysts to produce numerous natural products ranging from commodity chemicals to pharmaceuticals. Protein engineering has emerged as a powerful biotechnological toolbox in the development of metabolic engineering, particularly for the biosynthesis of natural products. Recently, protein engineering has become a favored method to improve enzymatic activity, increase enzyme stability, and expand product spectra in natural product biosynthesis. This review summarizes recent advances and typical strategies in protein engineering, highlighting the paramount role of protein engineering in improving and diversifying the biosynthesis of natural products. Future prospects and research directions are also discussed.

Evaluating the Potential of T Cell Receptor Repertoires in Predicting the Prognosis of Resectable Non-Small Cell Lung Cancers

For resectable cancer patients, a method that could precisely predict the risk of postoperative recurrence would be crucial for guiding adjuvant treatment. Since T cell receptor (TCR) repertoires had been shown to be closely related to the dynamics of cancers, here we enrolled a cohort of patients to evaluate the potential of TCR repertoires in predicting the prognosis of resectable non-small cell lung cancers. Specifically, TCRβ repertoires were analyzed in surgical tumor tissues and matched adjacent non-tumor tissues from 39 patients enrolled with resectable non-small cell lung cancer, through target enrichment and high-throughput sequencing. As a result, there are significant differences between the TCR repertories of tumor samples and those of matched adjacent non-tumor samples as evaluated by criteria like the number of clonotypes. In addition, TCR repertoires were significantly associated with a few clinical features, as well as somatic mutations. Finally, certain TCRβ variable-joining (V-J) pairings were featured to build a logistic regression model in predicting postoperative recurrence of resectable non-small cell lung cancers with a testing area under the receiver operating characteristic curve (AUC) of around 0.9. Thus, we hypothesize that TCR repertoires could be potentially used to predict prognosis after curative surgery for non-small cell lung cancer patients.

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.

Virus-Induced Gene Silencing to Investigate Alkaloid Biosynthesis in Opium Poppy

Virus-induced gene silencing (VIGS) enables the targeted silencing of genes in opium poppy (Papaver somniferum) and has been used extensively to determine or support the physiological functions of benzylisoquinoline alkaloid biosynthetic enzymes. Here we describe detailed protocols involved in the application of VIGS to investigate BIA metabolism in opium poppy.

3'O-Methyltransferase, Ps3'OMT, from opium poppy: involvement in papaverine biosynthesis

Using, in silico, in vitro and in planta functional assays, we demonstrate that Ps3'OMT, an 3'-O methyl transferase is linked to papaverine biosynthesis in opium poppy. Papaverine, one of the benzylisoquinoline alkaloids (BIA) synthesized in the medicinally important plant, Papaver somniferum, is known for the potent pharmacological properties. Papaverine biosynthesis has remained debatable as two different pathways, NH (involving N-desmethylated intermediates) and the NCH₃ (involving N-methylated intermediates), have been proposed. In addition, there are several intermediate steps in both the proposed pathways that are not very well characterized in terms of specific enzymes. In this study, we report the identification and functional characterization of 3'O-methyltransferase (Ps3'OMT) which might participate in the 3'O-methylation of the intermediates in the papaverine biosynthesis. Comparison of transcript and metabolite profiles of high and low papaverine producing cultivar revealed the occurrence of a 3'O-methyltransferase, Ps3'OMT, which was abundant in aerial organs and shared 72% identity with the GfLOMT7 predicted to have 3'OMT activity. In silico studies based on homology modeling, docking and MD simulations predicted (S)-norlaudanine as the potential substrate forming a stable complex with Ps3'OMT. Suppression of Ps3'OMT through virus-induced gene silencing resulted in a remarkable decrease in the level of papaverine in comparison to control plants. The characterization of the functionally unique Ps3'OMT involved in BIA metabolism suggests an involvement of the NH pathway leading to papaverine biosynthesis.

An Asymmetric Reductase That Intercepts Acyclic Imino Acids Produced in Situ by a Partner Oxidase

Acyclic imines are unstable in aqueous conditions. For this reason, known imine reductases, which enable the synthesis of chiral amines, mainly intercept stable cyclic imines. Here we report the detailed biochemical and structural characterization of Bsp5, an imino acid reductase from the d-2-hydroxyacid dehydrogenase family that reduces acyclic imino acids produced in situ by a partner oxidase. We determine a 1.6 Å resolution structure of Bsp5 in complex with d-arginine and coenzyme NADPH. Combined with mutagenesis work, our study reveals the minimal structural constraints for its biosynthetic activity. Furthermore, we demonstrate that Bsp5 can intercept more complex products from an alternate oxidase partner, suggesting that this oxidase-imino acid reductase pair could be evolved for biocatalytic conversion of l-amino acids to d-amino acids.

Synthetic biology strategies for microbial biosynthesis of plant natural products

Metabolic engineers endeavor to create a bio-based manufacturing industry using microbes to produce fuels, chemicals, and medicines. Plant natural products (PNPs) are historically challenging to produce and are ubiquitous in medicines, flavors, and fragrances. Engineering PNP pathways into new hosts requires finding or modifying a suitable host to accommodate the pathway, planning and implementing a biosynthetic route to the compound, and discovering or engineering enzymes for missing steps. In this review, we describe recent developments in metabolic engineering at the level of host, pathway, and enzyme, and discuss how the field is approaching ever more complex biosynthetic opportunities.