Exploiting members of the BAHD acyltransferase family to synthesize multiple hydroxycinnamate and benzoate conjugates in yeast

Family characteristics, phylogenetic reconstruction, and potential applications of the plant BAHD acyltransferase family

The BAHD acyltransferase family is a class of proteins in plants that can acylate a variety of primary and specialized secondary metabolites. The typically acylated products have greatly improved stability, lipid solubility, and bioavailability and thus show significant differences in their physicochemical properties and pharmacological activities. Here, we review the protein structure, catalytic mechanism, and phylogenetic reconstruction of plant BAHD acyltransferases to describe their family characteristics, acylation reactions, and the processes of potential functional differentiation. Moreover, the potential applications of the BAHD family in human activities are discussed from the perspectives of improving the quality of economic plants, enhancing the efficacy of medicinal plants, improving plant biomass for use in biofuel, and promoting stress resistance of land plants. This review provides a reference for the research and production of plant BAHD acyltransferases.

Coordinating caffeic acid and salvianic acid A pathways for efficient production of rosmarinic acid in Escherichia coli

Rosmarinic acid is a natural hydroxycinnamic acid ester used widely in the food and pharmaceutical industries. Although many attempts have been made to screen rate-limiting enzymes and optimize modules through co-culture fermentation, the titer of rosmarinic acid remains at the microgram level by microorganisms. A de novo biosynthetic pathway for rosmarinic acid was constructed based on caffeic acid synthesis modules in Escherichia coli. Knockout of competing pathways increased the titer of rosmarinic acid and reduced the synthesis of rosmarinic acid analogues. An L-amino acid deaminase was introduced to balance metabolic flux between the synthesis of caffeic acid and salvianic acid A. The ratio of FADH₂/FAD was maintained via the coordination of deaminase and HpaBC, which is responsible for caffeic acid synthesis. Knockout of menI, encoding an endogenous thioesterase, increased the stability of caffeoyl-CoA. The final strain produced 5780.6 mg/L rosmarinic acid in fed-batch fermentation, the highest yet reported for microbial production. The strategies applied in this study lay a foundation for the synthesis of other caffeic acid and rosmarinic acid derivatives.

Molecular evolution and structural analyses of proteins involved in metabolic pathways of volatile organic compounds in Petunia hybrida (Solanaceae)

The association between plants and their pollinators is essential for increasing the diversity in angiosperms. Morphological and physiological traits, mainly floral scent, can influence the pollination dynamics and select pollinators for each plant species. In this work, we studied two proteins involved in producing volatile organic compounds in plants, conyferyl alcohol acyltransferase (CFAT) and benzoyl-CoA:benzyl alcohol/phenyl ethanol benzoyl transferase (BPBT) genes. We aimed to understand these proteins with respect to evolutionary and structural aspects and functions in Solanaceae using phylogenetic methods and comparative molecular modeling. We used Bayesian inference to describe the proteins' evolutionary history using Petunia x hybrida as a query to search for homologs in the Solanaceae family. Theoretical 3D models were obtained for both proteins using Panicum virgatum as a template. The phylogenetic tree included several different enzymes with diverse biological roles in Solanaceae, displaying the transferase domain. We identified only one sequence of CFAT in the databases, which belongs to Petunia x hybrida, and found several BPBT sequences from the genera Nicotiana, Solanum, and Capsicum. The 3D structures of CFAT and BPBT have two different domains, and we have identified the amino acid residues essential for the enzymatic activity and interaction with substrates.

Advances in Production of Hydroxycinnamoyl-Quinic Acids: From Natural Sources to Biotechnology

Hydroxycinnamoyl-quinic acids (HCQAs) are polyphenol esters formed of hydroxycinnamic acids and (-)-quinic acid. They are naturally synthesized by plants and some micro-organisms. The ester of caffeic acid and quinic acid, the chlorogenic acid, is an intermediate of lignin biosynthesis. HCQAs are biologically active dietary compounds exhibiting several important therapeutic properties, including antioxidant, antimicrobial, anti-inflammatory, neuroprotective, and other activities. They can also be used in the synthesis of nanoparticles or drugs. However, extraction of these compounds from biomass is a complex process and their synthesis requires costly precursors, limiting the industrial production and availability of a wider variety of HCQAs. The recently emerged production through the bioconversion is still in an early stage of development. In this paper, we discuss existing and potential future strategies for production of HCQAs.

Consecutive action of two BAHD acyltransferases promotes tetracoumaroyl spermine accumulation in chicory

Fully substituted phenolamide accumulation in the pollen coat of Eudicotyledons is a conserved evolutionary chemical trait. Interestingly, spermidine derivatives are replaced by spermine derivatives as the main phenolamide accumulated in the Asteraceae family. Here, we show that the full substitution of spermine in chicory (Cichorium intybus) requires the successive action of two enzymes, that is spermidine hydroxycinnamoyl transferase-like proteins 1 and 2 (CiSHT1 and CiSHT2), two members of the BAHD enzyme family. Deletion of these genes in chicory using CRISPR/Cas9 gene editing technology evidenced that CiSHT2 catalyzes the first N-acylation steps, whereas CiSHT1 fulfills the substitution to give rise to tetracoumaroyl spermine. Additional experiments using Nicotiana benthamiana confirmed these findings. Expression of CiSHT2 alone promoted partially substituted spermine accumulation, and coexpression of CiSHT2 and CiSHT1 promoted synthesis and accumulation of the fully substituted spermine. Structural characterization of the main product of CiSHT2 using nuclear magnetic resonance revealed that CiSHT2 preferentially catalyzed N-acylation of secondary amines to form N5,N10-dicoumaroyl spermine, whereas CiSHT1 used this substrate to synthesize tetracoumaroyl spermine. We showed that spermine availability may be a key determinant toward preferential accumulation of spermine derivatives over spermidine derivatives in chicory. Our results reveal a subfunctionalization among the spermidine hydroxycinnamoyl transferase that was accompanied by a modification of free polyamine metabolism that has resulted in the accumulation of this new phenolamide in chicory and most probably in all Asteraceae. Finally, genetically engineered yeast (Saccharomyces cerevisiae) was shown to be a promising host platform to produce these compounds.

Engineering Saccharomyces cerevisiae for production of the capsaicinoid nonivamide

Background

Capsaicinoids are produced by plants in the Capsicum genus and are the main reason for the pungency of chili pepper fruits. They are strong agonists of TRPV1 (the transient receptor potential cation channel subfamily V member 1) and used as active ingredients in pharmaceuticals for the treatment of pain. The use of bioengineered microorganisms in a fermentation process may be an efficient route for their preparation, as well as for the discovery of (bio-)synthetic capsaicinoids with improved or novel bioactivities.

Results

Saccharomyces cerevisiae was engineered to over-express a selection of amide-forming N-acyltransferase and CoA-ligase enzyme cascades using a combinatorial gene assembly method, and was screened for nonivamide production from supplemented vanillylamine and nonanoic acid. Data from this work demonstrate that Tyramine N-hydroxycinnamoyl transferase from Capsicum annuum (CaAT) was most efficient for nonivamide formation in yeast, outcompeting the other candidates including AT3 (Pun1) from Capsicum spp. The CoA-ligase partner with highest activity from the ones evaluated here were from Petunia hybrida (PhCL) and Spingomonas sp. Ibu-2 (IpfF). A yeast strain expressing CaAT and IpfF produced 10.6 mg L⁻¹ nonivamide in a controlled bioreactor setup, demonstrating nonivamide biosynthesis by S. cerevisiae for the first time.

Conclusions

Baker’s yeast was engineered for production of nonivamide as a model capsaicinoid, by expressing N-acyltransferases and CoA-ligases of plant and bacterial origin. The constructed yeast platform holds potential for in vivo biocatalytic formation of capsaicinoids and could be a useful tool for the discovery of novel drugs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01831-3.

Towards engineered yeast as production platform for capsaicinoids

Capsaicinoids are bioactive alkaloids produced by the chili pepper fruit and are known to be the most potent agonists of the human pain receptor TRPV1 (Transient Receptor Potential Cation Channel Subfamily V Member 1). They are currently produced by extraction from chili pepper fruit or by chemical synthesis. Transfer of the biosynthetic route to a microbial host could enable more efficient capsaicinoid production by fermentation and may also enable the use of synthetic biology to create a diversity of new compounds with potentially improved properties. This review summarises the current state of the art on the biosynthesis of capsaicinoid precursors in baker's yeast, Saccharomyces cerevisiae, and discusses bioengineering strategies for achieving total synthesis from sugar.

Identification and characterization of a set of monocot BAHD monolignol transferases

Plant BAHD acyltransferases perform a wide range of enzymatic tasks in primary and secondary metabolism. Acyl-CoA monolignol transferases, which couple a CoA substrate to a monolignol creating an ester linkage, represent a more recent class of such acyltransferases. The resulting conjugates may be used for plant defense but are also deployed as important "monomers" for lignification, in which they are incorporated into the growing lignin polymer chain. p-Coumaroyl-CoA monolignol transferases (PMTs) increase the production of monolignol p-coumarates, and feruloyl-CoA monolignol transferases (FMTs) catalyze the production of monolignol ferulate conjugates. We identified putative FMT and PMT enzymes in sorghum (Sorghum bicolor) and switchgrass (Panicum virgatum) and have compared their activities to those of known monolignol transferases. The putative FMT enzymes produced both monolignol ferulate and monolignol p-coumarate conjugates, whereas the putative PMT enzymes produced monolignol p-coumarate conjugates. Enzyme activity measurements revealed that the putative FMT enzymes are not as efficient as the rice (Oryza sativa) control OsFMT enzyme under the conditions tested, but the SbPMT enzyme is as active as the control OsPMT enzyme. These putative FMTs and PMTs were transformed into Arabidopsis (Arabidopsis thaliana) to test their activities and abilities to biosynthesize monolignol conjugates for lignification in planta. The presence of ferulates and p-coumarates on the lignin of these transformants indicated that the putative FMTs and PMTs act as functional feruloyl-CoA and p-coumaroyl-CoA monolignol transferases within plants.

Alleviation of the Byproducts Formation Enables Highly Efficient Biosynthesis of Rosmarinic Acid in Saccharomyces cerevisiae

Rosmarinic acid as a polyphenolic compound has great values in the pharmaceutical, cosmetic, and food industries. To achieve efficient biosynthesis of rosmarinic acid, the major obstacles such as imbalanced metabolic flux among branching pathways and substrate promiscuity of pathway enzymes should be eliminated. Here, a rosmarinic acid producing Saccharomyces cerevisiae strain was constructed by introducing codon optimized d-lactate dehydrogenase gene mutant (OD-LDHY52A), 4-coumarate CoA ligase gene (OPc4CL2), and rosmarinic acid synthase gene (OMoRAS) into a previously constructed caffeic acid hyper-producer. To identify the metabolic bottleneck, the substrate specificity of OPc4CL2 and OMoRAS was figured out by bioconversion experiments and HPLC-MS/MS analysis. Subsequently, the byproducts formation was alleviated by removing prephenate dehydratase and tuning down the expression level of OPc4CL2. The final strain YRA113-15B produced 208 mg/L rosmarinic acid in a shake-flask culture (a 63-fold improvement over the initial strain), which was the highest rosmarinic acid titer by engineered microbial cells reported to date. This work provides a promising platform for fermentative production of rosmarinic acid and offers a strategy to overcome the intrapathway competition.

Systematic identification and expression profiles of the BAHD superfamily acyltransferases in barley (Hordeum vulgare)

BAHD superfamily acyltransferases play an important role in catalyzing and regulating secondary metabolism in plants. Despite this, there is relatively little information regarding the BAHD superfamily in barley. In this study, we identified 116 HvBAHD acyltransferases from the barley genome. Based on phylogenetic analysis and classification in model monocotyledonous and dicotyledonous plants, we divided the genes into eight groups, I-a, I-b, II, III-a, III-b, IV, V-a and V-b. The Clade IV genes, including Agmatine Coumarol Transferase (ACT) that is associated with resistance of plants to Gibberella fungi, were absent in Arabidopsis. Cis-regulatory element analysis of the HvBAHDs showed that the genes respond positively to GA3 treatment. In-silico expression and qPCR analysis showed the HvBAHD genes are expressed in a range of tissues and developmental stages, and highly enriched in the seedling stage, consistent with diverse roles. Single nucleotide polymorphism (SNP) scanning analysis revealed that the natural variation in the coding regions of the HvBAHDs is low and the sequences have been conserved during barley domestication. Our results reveal the complexity of the HvBAHDs and will help facilitate their analysis in further studies.

De novo Biosynthesis of Salvianolic Acid B in Saccharomyces cerevisiae Engineered with the Rosmarinic Acid Biosynthetic Pathway

Salvianolic acid B (SAB), also named lithospermic acid B, belongs to a class of water-soluble phenolic acids, originating from plants such as Salvia miltiorrhiza. SAB exhibits a variety of biological activities and has been clinically used to treat cardio- and cerebrovascular diseases and also has great potential as a health care product and medicine for other disorders. However, its biosynthetic pathway has not been completely elucidated. Here, we report the de novo biosynthesis of SAB in Saccharomyces cerevisiae engineered with the heterologous rosmarinic acid (RA) biosynthetic pathway. The created pathway contains seven genes divided into three modules on separate plasmids, pRS424-FjTAL-Sm4CL2, pRS425-SmTAT-SmHPPR or pRS425-SmTAT-CbHPPR, and pRS426-SmRAS-CbCYP-CbCPR. These three modules were cotransformed into S. cerevisiae, resulting in the recombinant strains YW-44 and YW-45. Incubation of the recombinant strains in a basic medium without supplementing any substrates yielded 34 and 30 μg/L of SAB. The findings in this study indicate that the created heterologous RA pathway cooperates with the native metabolism of S. cerevisiae to enable the de novo biosynthesis of SAB. This provides a novel insight into a biosynthesis mechanism of SAB and also lays the foundation for the production of SAB using microbial cell factories.

Metagenomic Insights into the Composition and Function of Microbes Associated with the Rootzone of Datura inoxia

The purpose of this paper is to elucidate the roles that microbes may be playing in the rootzone of the medicinal plant Daturainoxia. We hypothesized that the microbes associated with the Datura rootzone would be significantly different than the similar surrounding fields in composition and function. We also hypothesized that rhizospheric and endophytic microbes would be associated with similar metabolic functions to the plant rootzone they inhabited. The methods employed were microbial barcoding, tests of essential oils against antibiotic resistant bacteria and other soil bacterial isolates, 16S Next Generation Sequencing (NGS) metabarcoding, and Whole Genome Shotgun (WGS) taxonomic and functional analyses. A few of the main bacterial genera of interest that were differentially abundant in the Datura root microbiome were Flavobacterium (p = 0.007), Chitinophaga (p = 0.0007), Pedobacter (p = 6 × 10−5), Bradyhizobium (p = 1 × 10−8), and Paenibacillus (p = 1.46 × 10−6). There was significant evidence that the microbes associated with the Datura rootzone had elevated function related to bacterial chalcone synthase (p = 1.49 × 10−3) and permease genes (p < 0.003). There was some evidence that microbial functions in the Datura rootzone provided precursors to important plant bioactive molecules or were beneficial to plant growth. This is important because these compounds are phyto-protective antioxidants and are precursors to many aromatic bioactive compounds that are relevant to human health. In the context of known interactions, and current results, plants and microbes influence the flavonoid biosynthetic pathways of one other, in terms of the regulation of the phenylpropanoid pathway. This is the first study to focus on the microbial ecology of the Datura rootzone. There are possible biopharmaceutical and agricultural applications of the natural interplay that was discovered during this study of the Datura inoxia rhizosphere.

Tools for protein structure prediction and for molecular docking applied to enzyme active site analysis: A case study using a BAHD hydroxycinnamoyltransferase

Elucidating the structure of an enzyme and how substrates bind to the active site is an important step for understanding its reaction mechanism and function. Nevertheless, the methods available to obtain three-dimensional structures of proteins, such as x-ray crystallography and NMR, can be expensive and time-consuming. Considering this, an alternative is using structural bioinformatic tools to predict the tertiary structure of a protein from its primary sequence, followed by molecular docking of one or more substrates into the enzyme structure model. In the past few years, significant advances have been made in these computational tools, which can give useful information about the active site and enzyme-substrate interactions before the structure can be resolved using physical methods. Here, using common bean (Phaseolus vulgaris) hydroxycinnamoyl-coenzyme A:tetrahydroxyhexanedioic acid hydroxycinnamoyltransferase (HHHT) as an example, we describe methods and workflows for protein structure prediction and molecular docking that can be performed on a personal computer using only open-source tools.

Catalytic function, mechanism, and application of plant acyltransferases

Acyltransferases (ATs) are important tailoring enzymes that contribute to the diversity of natural products. They catalyze the transfer of acyl groups to the skeleton, which improves the lipid solubility, stability, and pharmacological activity of natural compounds. In recent years, a number of ATs have been isolated from plants. In this review, we have summarized 141 biochemically characterized ATs during the period July 1997 to October 2020, including their function, heterologous expression systems, and catalytic mechanisms. Their catalytic performance and application potential has been further discussed.

Approaches for the enzymatic synthesis of alkyl hydroxycinnamates and applications thereof

Alkyl hydroxycinnamates (AHs) is a group of molecules of biotechnological interest due to their cosmetic, food, and pharmaceutical applications. Among their most interesting uses are as UV protectants, skin depigmentation agents, and antioxidant ingredients which are often claimed for their antitumoral potential. Nowadays, many sustainable enzymatic approaches using low-cost starting materials are available and interesting immobilization techniques are helping to increase the reuse of the biocatalysts, allowing the intensification of the processes and increasing AHs accessibility. Here a convenient summary of AHs most interesting biological activities and possible applications is presented. A deeper analysis of the art state to obtain AHs, focusing on most employed enzymatic synthesis approaches, their sustainability, acyl donors relevance, and most interesting enzyme immobilization strategies is provided.Key points• Most interesting alkyl hydroxycinnamates applications are summarized.• Enzymatic approaches to obtain alkyl hydroxycinnamates are critically discussed.• Outlook of enzyme immobilization strategies to attain alkyl hydroxycinnamates.

Identification and characterization of piperine synthase from black pepper, Piper nigrum L

Black pepper (Piper nigrum L.) is the world's most popular spice and is also used as an ingredient in traditional medicine. Its pungent perception is due to the interaction of its major compound, piperine (1-piperoyl-piperidine) with the human TRPV-1 or vanilloid receptor. We now identify the hitherto concealed enzymatic formation of piperine from piperoyl coenzyme A and piperidine based on a differential RNA-Seq approach from developing black pepper fruits. This enzyme is described as piperine synthase (piperoyl-CoA:piperidine piperoyl transferase) and is a member of the BAHD-type of acyltransferases encoded by a gene that is preferentially expressed in immature fruits. A second BAHD-type enzyme, also highly expressed in immature black pepper fruits, has a rather promiscuous substrate specificity, combining diverse CoA-esters with aliphatic and aromatic amines with similar efficiencies, and was termed piperamide synthase. Recombinant piperine and piperamide synthases are members of a small gene family in black pepper. They can be used to facilitate the microbial production of a broad range of medicinally relevant aliphatic and aromatic piperamides based on a wide array of CoA-donors and amine-derived acceptors, offering widespread applications.

Exploiting Spermidine N-Hydroxycinnamoyltransferase Diversity and Substrate Promiscuity to Produce Various Trihydroxycinnamoyl Spermidines and Analogues in Engineered Yeast

Trihydroxycinnamoyl spermidines (THCSpd) are plant specialized metabolites with promising pharmacological activities as antifungals, antibacterial, antiviral, and antidepressant drugs. However, their characterization and potential pharmaceutical exploitation are greatly impaired by the sourcing of these compounds, restricted to the pollen of core Eudicot plant species. In this work, we developed a precursor-directed biosynthesis of THCSpd in yeast using a dual enzymatic system based on 4-coumarate-CoA ligases (4CL) and spermidine N-hydroxycinnamoyltransferases (SHT). The system relies on the yeast endogenous spermidine pool and only requires hydroxycinnamic acids as exogenous precursors. By exploring 4CL isoforms and SHT diversity among plants, we have driven the production of 8 natural THCSpd, using single or mixed hydroxycinnamic acid precursors. Substrate promiscuities of 4CL and SHT were genuinely exploited to produce 8 new-to-nature THCSpd from exotic hydroxycinnamic and dihydrohydroxycinnamic acids, together with 3 new-to-nature THCSpd containing halogenated hydroxycinnamoyl moieties. In this work, we established a versatile and modular biotechnological production platform allowing the tailor-made THCSpd synthesis, constituting pioneer metabolic engineering for access to these valuable natural products.

Phenolamides: Plant specialized metabolites with a wide range of promising pharmacological and health-promoting interests

Phenolamides constitute a family of metabolites, widely represented in the plant kingdom, that can be found in all plant organs with a predominance in flowers and pollen grains. They represent a large and structurally diverse family, resulting from the association of phenolic acids with aliphatic or aromatic amines. Initially revealed as active compounds in several medicinal plant extracts, phenolamides have been extensively studied for their health-promoting and pharmacological properties. Indeed, phenolamides have been shown to exhibit antioxidant, anti-inflammatory, anti-cancer and antimicrobial properties, but also protective effects against metabolic syndrome and neurodegenerative diseases. The purpose of this review is to summarise this large body of literature, including in vitro and in vivo studies, by describing the diversity of their biological properties and our actual knowledge of the molecular mechanisms behind them. With regard to their considerable pharmacological interest, the question of industrial production is also tackled through chemical and biological syntheses in engineered microorganisms. The diversity of biological activities already described, together with the active discovery of the broad structural diversity of this metabolite family, make phenolamides a promising source of new active compounds on which future studies should be focused.

Towards renewable flavors, fragrances, and beyond

Esters constitute a large space of unique molecules with broad range of applications as flavors, fragrances, pharmaceuticals, cosmetics, green solvents, and advanced biofuels. Global demand of natural esters in food, household cleaner, personal care, and perfume industries is increasing while the ester supply from natural sources has been limited. Development of novel microbial cell factories for ester production from renewable feedstocks can potentially provide an alternative and sustainable source of natural esters and hence help fulfill growing demand. Here, we highlight recent advances in microbial production of esters and provide perspectives for improving its economic feasibility. As the field matures, microbial ester production platforms will enable renewable and sustainable production of flavors and fragrances, and open new market opportunities beyond what nature can offer.

Phenolic cross-links: building and de-constructing the plant cell wall

Covering: Up to 2019Phenolic cross-links and phenolic inter-unit linkages result from the oxidative coupling of two hydroxycinnamates or two molecules of tyrosine. Free dimers of hydroxycinnamates, lignans, play important roles in plant defence. Cross-linking of bound phenolics in the plant cell wall affects cell expansion, wall strength, digestibility, degradability, and pathogen resistance. Cross-links mediated by phenolic substituents are particularly important as they confer strength to the wall via the formation of new covalent bonds, and by excluding water from it. Four biopolymer classes are known to be involved in the formation of phenolic cross-links: lignins, extensins, glucuronoarabinoxylans, and side-chains of rhamnogalacturonan-I. Lignins and extensins are ubiquitous in streptophytes whereas aromatic substituents on xylan and pectic side-chains are commonly assumed to be particular features of Poales sensu lato and core Caryophyllales, respectively. Cross-linking of phenolic moieties proceeds via radical formation, is catalyzed by peroxidases and laccases, and involves monolignols, tyrosine in extensins, and ferulate esters on xylan and pectin. Ferulate substituents, on xylan in particular, are thought to be nucleation points for lignin polymerization and are, therefore, of paramount importance to wall architecture in grasses and for the development of technology for wall disassembly, e.g. for the use of grass biomass for production of 2^nd generation biofuels. This review summarizes current knowledge on the intra- and extracellular acylation of polysaccharides, and inter- and intra-molecular cross-linking of different constituents. Enzyme mediated lignan in vitro synthesis for pharmaceutical uses are covered as are industrial exploitation of mutant and transgenic approaches to control cell wall cross-linking.

Engineering a microbial biosynthesis platform for de novo production of tropane alkaloids

Tropane alkaloids (TAs) are a class of phytochemicals produced by plants of the nightshade family used for treating diverse neurological disorders. Here, we demonstrate de novo production of tropine, a key intermediate in the biosynthetic pathway of medicinal TAs such as scopolamine, from simple carbon and nitrogen sources in yeast (Saccharomyces cerevisiae). Our engineered strain incorporates 15 additional genes, including 11 derived from diverse plants and bacteria, and 7 disruptions to yeast regulatory or biosynthetic proteins to produce tropine at titers of 6 mg/L. We also demonstrate the utility of our engineered yeast platform for the discovery of TA derivatives by combining biosynthetic modules from distant plant lineages to achieve de novo production of cinnamoyltropine, a non-canonical TA. Our engineered strain constitutes a starting point for future optimization efforts towards realizing industrial fermentation of medicinal TAs and a platform for the synthesis of TA derivatives with enhanced bioactivities.

Tropane alkaloids (TAs) are a group of phytochemicals that are used to treat neurological disorders. Here, the authors engineer baker’s yeast to produce tropine, a key intermediate in the biosynthetic pathway of TAs, and cinnamoyltropine, a non-canonical TA, from simple carbon and nitrogen sources.

Production of clovamide and its analogues in Saccharomyces cerevisiae and Lactococcus lactis

Clovamide and its analogues are N-hydroxycinnamoyl-L-amino acids (HAA) that exhibit antioxidant activities. For environmental and economic reasons, biological synthesis of these plant-derived metabolites has garnered interest. In this study, we exploited HDT1, a BAHD acyltransferase recently isolated from red clover, for the production of clovamide and derivatives in S. cerevisiae and L. lactis. HDT1 catalyses the transfer of hydroxycinnamoyl-coenzyme A (CoA) onto aromatic amino acids. Therefore, by heterologously co-expressing HDT1 with 4-coumarate:CoA ligase (4CL), we succeeded in the biological production of clovamide and more than 20 other HAA, including halogenated ones, upon feeding the engineered micro-organisms with various combinations of cinnamates and amino acids. To the best of our knowledge, this is the first report on the biological synthesis of HAA and, more generally, on the synthesis of plant-derived antioxidant phenolic compounds in L. lactis. The production of these health beneficial metabolites in Generally Recognized As Safe (GRAS) micro-organisms such as S. cerevisiae and L. lactis provides new options for their delivery as therapeutics. SIGNIFICANCE AND IMPACT OF THE STUDY: N-hydroxycinnamoyl-L-amino acids such as clovamide are bioactive plant-derived phenolic compounds with health beneficial effects. Relying on chemical synthesis or direct extraction from plant sources for the supply of these valuable molecules poses challenges to environmental sustainability. As an alternative route, this work demonstrates the potential for biological synthesis of N-hydroxycinnamoyl-L-amino acids using engineered microbial hosts such as Saccharomyces cerevisiae and Lactococcus lactis. Besides being more eco-friendly, this approach should also provide more structurally diverse compounds and offer new methods for their delivery to the human body.

Biosynthesis of angelyl-CoA in Saccharomyces cerevisiae

Background

The angelic acid moiety represents an essential modification in many biologically active products. These products are commonly known as angelates and several studies have demonstrated their therapeutic benefits, including anti-inflammatory and anti-cancer effects. However, their availability for use in the development of therapeutics is limited due to poor extraction yields. Chemical synthesis has been achieved but its complexity prevents application, therefore microbial production may offer a promising alternative. Here, we engineered the budding yeast Saccharomyces cerevisiae to produce angelyl-CoA, the CoA-activated form of angelic acid.

Results

For yeast-based production of angelyl-CoA we first expressed genes recently identified in the biosynthetic cluster ssf of Streptomyces sp. SF2575 in S. cerevisiae. Exogenous feeding of propionate and heterologous expression of a propionyl-CoA synthase from Streptomyces sp. were initially employed to increase the intracellular propionyl-CoA level, resulting in production of angelyl-CoA in the order of 5 mg/L. Substituting the Streptomyces sp. propionyl-CoA carboxylase with a carboxylase derived from Streptomyces coelicolor resulted in angelyl-CoA levels up to 6.4 mg/L. In vivo analysis allowed identification of important intermediates in the pathway, including methyl-malonyl-CoA and 3-hydroxyl-2-methyl-butyryl-CoA. Furthermore, methyl-malonate supplementation and expression of matB CoA ligase from S. coelicolor allowed for methyl-malonyl-CoA synthesis and supported, together with parts of the ssf pathway, angelyl-CoA titres of approximately 1.5 mg/L. Finally, feeding of angelic acid to yeasts expressing acyl-CoA ligases from plant species led to angelyl-CoA production rates of approximately 40 mg/L.

Conclusions

Our results demonstrate the biosynthesis of angelyl-CoA in yeast from exogenously supplied carboxylic acid precursors. This is the first report on the activity of the ssf genes. We envision that our approach will provide a platform for a more sustainable production of the pharmaceutically important compound class of angelates.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0925-8) contains supplementary material, which is available to authorized users.

Tyrosine biosynthesis, metabolism, and catabolism in plants

L-Tyrosine (Tyr) is an aromatic amino acid (AAA) required for protein synthesis in all organisms, but synthesized de novo only in plants and microorganisms. In plants, Tyr also serves as a precursor of numerous specialized metabolites that have diverse physiological roles as electron carriers, antioxidants, attractants, and defense compounds. Some of these Tyr-derived plant natural products are also used in human medicine and nutrition (e.g. morphine and vitamin E). While the Tyr biosynthesis and catabolic pathways have been extensively studied in microbes and animals, respectively, those of plants have received much less attention until recently. Accumulating evidence suggest that the Tyr biosynthetic pathways differ between microbes and plants and even within the plant kingdom, likely to support the production of lineage-specific plant specialized metabolites derived from Tyr. The interspecies variations of plant Tyr pathway enzymes can now be used to enhance the production of Tyr and Tyr-derived compounds in plants and other synthetic biology platforms.

Engineering a bacterial platform for total biosynthesis of caffeic acid derived phenethyl esters and amides

Caffeic acid has been widely recognized as a versatile pharmacophore for synthesis of new chemical entities, among which caffeic acid derived phenethyl esters and amides are the most extensively-investigated bioactive compounds with potential therapeutical applications. However, the natural biosynthetic routes for caffeic acid derived phenethyl esters or amides remain enigmatic, limiting their bio-based production. Herein, product-directed design of biosynthetic schemes allowed the development of thermodynamically favorable pathways for these compounds via acyltransferase (ATF) mediated trans-esterification. Production based screening identified a microbial O-ATF from Saccharomyces cerevisiae and a plant N-ATF from Capsicum annuum capable of forming caffeic acid derived esters and amides, respectively. Subsequent combinatorial incorporation of caffeic acid with various aromatic alcohol or amine biosynthetic pathways permitted the de novo bacterial production of a panel of caffeic acid derived phenethyl esters or amides in Escherichia coli for the first time. Particularly, host strain engineering via systematic knocking out endogenous caffeoyl-CoA degrading thioesterase and pathway optimization via titrating co-substrates enabled production enhancement of five caffeic acid derived phenethyl esters and amides, with titers ranging from 9.2 to 369.1mg/L. This platform expanded the capabilities of bacterial production of high-value natural aromatic esters and amides from renewable carbon source via tailoring non-natural biosynthetic pathways.