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MEANtools integrates multi-omics data to identify metabolites and predict biosynthetic pathways.

During evolution, plants have developed the ability to produce a vast array of specialized metabolites, which play crucial roles in helping plants adapt to different environmental niches. However, their biosynthetic pathways remain largely elusive. In the past decades, increasing numbers of plant biosynthetic pathways have been elucidated based on approaches utilizing genomics, transcriptomics, and metabolomics. These efforts, however, are limited by the fact that they typically adopt a target-based approach, requiring prior knowledge. Here, we present MEANtools, a systematic and unsupervised computational integrative omics workflow to predict candidate metabolic pathways de novo by leveraging knowledge of general reaction rules and metabolic structures stored in public databases. In our approach, possible connections between metabolites and transcripts that show correlated abundance across samples are identified using reaction rules linked to the transcript-encoded enzyme families. MEANtools thus assesses whether these reactions can connect transcript-correlated mass features within a candidate metabolic pathway. We validate MEANtools using a paired transcriptomic-metabolomic dataset recently generated to reconstruct the falcarindiol biosynthetic pathway in tomato. MEANtools correctly anticipated five out of seven steps of the characterized pathway and also identified other candidate pathways involved in specialized metabolism, which demonstrates its potential for hypothesis generation. Altogether, MEANtools represents a significant advancement to integrate multi-omics data for the elucidation of biochemical pathways in plants and beyond.

Metabolomics

Identification and Catalytic Optimization of Pinene Oxidases in Paeoniflorin Biosynthetic Pathway.

Paeoniflorin is a pharmacologically important cage-like monoterpene glycoside characteristic of Paeonia plants, yet its biosynthetic pathway has remained largely unresolved, hindering sustainable production. Here, we confirmed that paeoniflorin biosynthesis originates from α-pinene and identified three novel cytochrome P450 enzymes that catalyze pinene oxidation. CYP71AN126 catalyzes the hydroxylation of α-pinene at positions C4 and C10, followed by further oxidation of the alcohol to a ketone at C4, whereas CYP76A225/226 exclusively catalyze C10 hydroxylation. Virus-induced gene silencing (VIGS) assays demonstrated that silencing CYP71AN126, but not CYP76A225 and CYP76A226, significantly reduced the paeoniflorin content, indicating that C4 hydroxylation plays an important role in paeoniflorin biosynthesis, whereas C10 hydroxylation is not. Through the analysis of natural sequence and activity divergence among CYP71AN126 and CYP76A225/226, combined with protein structure prediction and site-directed mutagenesis, we identified L493 as a critical residue involved in regulating catalytic site specificity and substrate specificity of CYP71AN126. Mutation of L493 reduced or eliminated the formation of undesired C10 hydroxylation side-product and enhanced substrate specificity. These findings establish C4 oxidation of α-pinene as the critical committed step in paeoniflorin biosynthesis. Our study lays a foundation for elucidating the complete biosynthetic pathway of paeoniflorin in Paeonia and provides a target for enzyme engineering of CYP71AN126 aimed at the efficient production of paeoniflorin via synthetic biology approaches.

Paeonia genus

Structural characterization and predicted biosynthetic pathway of the polysaccharide component of bioflocculant from starch-degrading Bacillus subtilis ZHX3.

Polysaccharides-based bioflocculant is a promising eco-friendly alternative to conventional flocculants, yet their application is limited by high production cost. Understanding the biosynthetic pathway is essential for targeted strain improvement. In this study, we characterized polysaccharides structure of bioflocculant MBF-ZHX3 from Bacillus subtilis ZHX3 and predicted its biosynthetic pathway via genomic analysis combined with quantitative real-time PCR (qPCR). Two purified polysaccharide fractions, PS1-1 (5982 Da) and PS2-1 (17,577 Da), were obtained. Both were mainly composed of glucose, with a backbone of →4)-α-D-Glcp-(1 → and α-D-Glcp-(1 → branches attached at O-6. Whole-genome sequencing revealed a circular chromosome of 4,122,369 bp and two plasmids. Functional annotation showed high carbohydrate metabolism activity, with 284 genes (9.52%) and 264 genes (11.28%) assigned to carbohydrate metabolism in the COG and KEGG database, respectively. A complete eps gene cluster consisting of 15 open reading frames was identified. qPCR showed that key genes involved in substrate uptake (ptsG, malP, mdxEFG-msmX) and nucleotide sugar synthesis (pgcA, gtaB) were significantly upregulated. The priming glycosyltransferase (GT) epsL and the primary GT epsF were upregulated, along with the flippase epsK, polymerase epsG, and chain-length regulators epsA and epsB. Based on these findings, we propose a putative biosynthetic pathway for the polysaccharide component of MBF-ZHX3, and identify epsL, epsF, and epsG as prioritized targets for future genetic engineering. This work provides an integrated structural-genomic-transcriptomic framework that can guide rational strain improvement to enhance bioflocculant production.

Polysaccharides structure

Immunological cross reactivity of four enzymes involved in the biosynthetic pathway of lysine, methionine and threonine in Escherichia coli K12.

In Escherichia coli K12 the biosynthetic pathway of lysine, methionine and threonine is characterized by three isofunctional aspartokinases and two homoserine dehydrogenases. A single polypeptide chain carries the threonine-sensitive aspartokinase and homoserine dehydrogenase (AK I-HDH I), and a different polypeptide chain carries the methionine-repressible aspartokinase and homoserine dehydrogenase (AK II-HDH II). Immuno-adsorbants prepared with rabbit antibodies against AK I-HDH I bind the lysine-sensitive aspartokinase (AK III), the AK II-HDH II, and the homoserine kinase (HSK), an enzyme of the threonine biosynthetic pathway. Saturation of the immunoadsorbant with AK I-HDH I results in a decreased binding capacity for the other enzymes. Displacement of bound AK III or HSK can be obtained with pure AK I-HDH I, showing that the affinity of the antibodies to homologous antigens is higher than to heterologous ones. Immunoadsorbants prepared with anti-HSK antibodies show the same type of recognition: binding of the three aspartkinases and a capacity to displace the heterologous antigens bound. Accordingly, the same antibodies, implicated in the binding of the homologous antigen, bind the other enzymes. None of the other enzymes of the pathway, or the other kinases tested are recognized by the two immunoadsorbants. It can be postulated that in E. coli K12, duplication of a common ancestor gene gave rise to the three aspartokinases and to the homoserine kinase; two of the genes coding for the aspartokinases fused with those coding for the homoserine dehydrogenases. Indicating that only few epitopes are shared by these enzymes, by conventional immuno-diffusion techniques no precipitation lines appeared with antibodies against AK I-HDH I and the other proteins.

Alcohol Oxidoreductases

A chromosome-level genome assembly of Lycoris radiata reveals the evolutionary origin of Amaryllidaceae alkaloids and elucidates the complete galanthamine biosynthetic pathway.

Amaryllidaceae alkaloids (AmAs) comprise a structurally diverse group of specialized metabolites produced almost exclusively by species of the Amaryllidoideae subfamily and are of substantial pharmacological importance. However, the limited availability of high-quality genomes from Amaryllidoideae plants has constrained systematic investigations of the genes and evolutionary processes underlying AmA biosynthesis. Here, we present a chromosome-level genome assembly of Lycoris radiata, which enabled the discovery of key downstream enzymes in the galanthamine biosynthetic pathway and uncovered reversible reactions between two critical metabolite pairs. These findings provide new mechanistic insight into pathway architecture and enable reconstruction of the galanthamine biosynthetic pathway in Yarrowia lipolytica. Comparative genomic analyses indicate that several core genes for AmA biosynthesis originated in ancestral angiosperms, whereas the complete pathway was likely assembled in the Amaryllidoideae subfamily through gene duplication and neofunctionalization. Furthermore, integrated metabolomic and transcriptomic analyses suggest that roots contribute actively to AmA metabolism in Lycoris. Together, these findings provide a genomic and biochemical framework for understanding the evolution and engineering of AmA biosynthesis.

Lycoris

Steroid secretion by in vitro perfused testes: testosterone biosynthetic pathways.

Alternative metabolic pathways for the biosynthesis of testosterone from pregnenolone exist in mammalian testes. The following experiments were designed to identify the preferred testosterone biosynthetic pathway in rat and rabbit testes. The experimental protocol included the infusion of steroidogenic reaction inhibitors and testosterone biosynthetic intermediates into testes perfused in vitro. Under these conditions, the testicular steroid secretions were a measure of specific reaction activities. Infusion of medrogestone (6,17-dimethyl-4,6-pregnadiene-3,20-dione, Ayerst), an inhibitor of delta5-4isomerization, permitted the reactions converting pregnenolone to androstenediol to be studied separately from those converting progesterone to testosterone. For example, the activity of the pregnenolone vector 17alpha-hydroxypregnenolone reaction was measured as the total of the 17alpha-hydroxypregnenolone, dehydroepiandrosterone, and androstenediol secreted by medrogestone-inhibited testes. The reactions convering delta5-3beta-hydroxysteroids to delta4-3-ketosteroids were studied in testes infused with SU-10603 (7-chloro-3,4-dihydro-2-[3-pyridyl]-1(2H)-naphthalenone. Ciba-Geigy), an inhibitor of 17alpha-hydroxylation and C-17, C-20 cleavage reactions. The results indicated that preferred testosterone biosynthetic pathways are present and different in rat and rabbit testes.

Animals

The Biosynthetic Pathway to the Pyrroloiminoquinone Marine Natural Product Ammosamide C.

Ammosamide C is a marine natural product containing a highly decorated pyrroloiminoquinone core. Studies on the biosynthetic gene cluster (BGC) that produces ammosamides previously revealed that they are made by a series of posttranslational modifications (PTMs). The BGC includes genes encoding a precursor peptide AmmA and four enzymes known as PEptide Aminoacyl-tRNA Ligases (PEARLs). Initial studies into the ammosamide biosynthetic pathway demonstrated Trp addition to a precursor peptide by the PEARL AmmB2. Thereafter, sequential modifications by several enzymes, including two other PEARLs lead to the formation of a peptide intermediate bearing a C-terminal diaminoquinone. In the present work, we present the biosynthetic steps that convert this intermediate to ammosamide C. The PEARL AmmB4 unexpectedly appends an arginine to the C-terminus of the aforementioned intermediate. Then, C-terminal proteolysis by the heterodimeric TldD/E-like protease Amm12/13 releases a dipeptide, which is subsequently cleaved by the dipeptidase Amm19 to produce a Trp-derived diaminoquinone. Amm3 next catalyzes the conversion of this Trp derivative to the corresponding chlorinated ammosamaic acid. Finally, a putative aminotransferase Amm20 performs an amidation, and Amm23 methylates this intermediate to arrive at ammosamide C; the order of these last two steps could not be determined definitively. This study reveals an unexpectedly lengthy route to ammosamide that illustrates the opportunistic nature of natural product biosynthesis, demonstrates a role for a PEARL that is unlike previous roles, identifies steps that are not PTMs, and adds Arg-tRNA to the growing repertoire of aminoacyl tRNAs that are used by PEARLs.

Biological Products

Repression of the tyrosine, lysine, and methionine biosynthetic pathways in a hisT mutant of Salmonella typhimurium.

A comparison was made of the repressibility of certain enzymes in the tyrosine, methionine, and lysine biosynthetic pathways in wild-type Salmonella typhimurium and a hisT mutant. The results show that (i) tyrosine represses the synthesis of the tyrosine-sensitive 3-deoxy-D-arabino-heptulsonic acid 7-phosphate synthetase and the tyrosine aminotransferase to the same extent in a hisT mutant as in wild type and (ii) there is no detectable alteration in the extent to which methionine represses O-succinylhomoserine synthetase or in the extent to which lysine represses the lysine-sensitive beta-aspartokinase as a result of the hisT mutation.

2-Isopropylmalate Synthase

Evolution of biosynthetic pathways: immunological approach.

Through the use of specific immunoadsorbent columns, it is shown that Escherichia coli aspartokinase I-homoserine dehydrogenase I, aspartokinase II-homoserine dehydrogenase II, aspartokinase III, and homoserine kinase, enzymes involved in the same complex biosynthetic pathway, share antigenic determinants. This raises the question of a common origin for the four cibtenoirart kinases. (Aspartate kinase or ATP:L aspartate 4-phosphotransferase, EC 2.7.2.4; homoserine dehydrogenase or Lhomoserine:NADP oxidoreductase, EC 1.1.1.3; homoserine kinase or ATP:L-homoserine O-phosphotransferase, EC 2.7.1.39.)

Alcohol Oxidoreductases

The immediate nucleotide precursor, guanosine triphosphate, in the riboflavin biosynthetic pathway.

In the present paper, the nucleotide precursor of riboflavin was investigated by experiments with labeled purines using non-growing cells of Eremothecium ashybii. The added purines, at 10(-4) M, were effectively incorporated into riboflavin at an early stage of riboflavin biosynthesis under the experimental conditions. In particular, both labeled xanthine and labeled guanine were specifically transported to guanosine nucleotides, GMP, GDP, GDP-Mannose and GTP, in the course of the riboflavin biosynthesis. A comparison of specific activities of labeled guanosine nucleotides and labeled riboflavin indicated that the nucleotide precursor of riboflavin is guanosine triphosphate. From the results obtained, a biosynthetic pathway of riboflavin is proposed under "DISCUSSION."

Ascomycota

Enzymatic innovations in Angelica pubescens reveal dual coumarin biosynthetic pathways driving metabolic diversification.

Coumarins are structurally diverse phenylpropanoid derivatives with ecological and pharmacological significance, yet the biosynthetic logic underlying their diversification remains incompletely understood in non-model medicinal plants. Angelica pubescens (Apiaceae), widely used in traditional Chinese medicine, accumulates a rich repertoire of furanocoumarins and dihydrofuranocoumarins, making it an ideal system to investigate this metabolic complexity. Here, we combined chromosome-level genome assembly, transcriptome and metabolite profiling, phylogenetics, and heterologous expression assays to dissect coumarin biosynthesis in A. pubescens. We identified two functionally specialized O-methyltransferases, ApOMT1 and ApOMT2, which catalyze regioselective methylation of xanthotoxol and bergaptol to yield the furanocoumarins xanthotoxin and bergapten. We also characterized ApCYP736A121, a cytochrome P450 enzyme that converts osthenol to the dihydrofuranocoumarin columbianetin via a previously unknown mechanism. Gene expression and metabolite accumulation patterns across tissues and developmental stages revealed functional partitioning among pathway branches. Phylogenetic and syntenic analyses indicated that ApOMT1 and ApOMT2 arose through subfunctionalization following gene duplication, whereas ApCYP736A121 evolved via neofunctionalization from a distantly related CYP736 ancestor. Together, our findings uncover dual biosynthetic routes to structurally distinct coumarins in A. pubescens and provide insights into the evolutionary mechanisms contributing to metabolic innovation in Apiaceae. This work lays a foundation for future efforts to engineer coumarin pathways and understand their ecological functions in medicinal plants.

Coumarins

Regulation of enzyme synthesis in the arginine biosynthetic pathway of Pseudomonas aeruginosa.

In Pseudomonas aeruginosa the synthesis of only two out of eight arginine biosynthetic enzymes tested was regulated. Comparisons were made between the specific activities of these enzymes in bacteria grown on arginine or on its precursor, glutamate. N2-Acetylornithine 5-aminotransferase (ACOAT), an enzyme involved in both the biosynthesis and catabolism of arginine, was induced about 14-fold during growth of the organism on arginine as the only carbon and nitrogen source, and the anabolic ornithine carbamoyltransferase (aOTC), a strictly biosynthetic enzyme, was repressed 18-fold. Addition of various carbon sources to the arginine medium led to repression of ACOAT and to derepression of aOTC. Fructose, which supported only slow growth of P. aeruginosa, had a weak regulatory effect on the synthesis of the two arginine enzymes while citrate, a good carbon source for this organism, had a strong effect. The repression of ACOAT by citrate was not relieved by adding cyclic AMP to the medium. Under a variety of growth conditions leading to different enzyme activities, a linear relationship between the reciprocal of the specific activity of ACOAT and the specific activity of aOTC was observed. This inverse regulation of the formation of the two enzymes suggested that a single regulatory system governs their synthesis. Such a view was supported by the isolation of citrate-resistant regulatory mutants which constitutively formed ACOAT at the induced level and aOTC at the repressed level.

Arginine

Pyrimidine biosynthetic pathway of Baccillus subtilis.

Biochemical and genetic data were obtained from a series of 51 Pyr- strains of Bacillus subtilis. The observed enzymatic deficiencies allowed the mutants to be placed into 12 clases, some of which represent defects in more than one of the six known pyrimidine biosynthetic enzymes. Mapping analysis by transformation has shown that all the Pyr- mutations are located in a single small area of the B. subtilis genome. A correlation of the biochemical defects and the genetic data has been made. Those mutations conferring similar enzymatic deficiencies were found to be contiguous on the B. subtilis map. Regulatory aspects of the pyrimidine pathway have also been investigated and are compared to previously reported results from other organisms. Evidence is presented which bears upon the possible physical association of the first three enzymes and the association of at least some of the enzymes of this pathway with particulate elements of the cell. A model for the organization of the enzymes is presented with dihydroorotate dehydrogenase as the central enzyme in a proposed aggregate.

Aspartate Carbamoyltransferase

Mechanism of suppression in Drosophila. V. Localization of the purple mutant of Drosophila melanogaster in the pteridine biosynthetic pathway.

The suppressible eye color mutant purple (pr) of Drosophila melanogaster is known to be unable to synthesize a wild-type complement of pteridine eye pigments. This study measures the reduced levels of drosopterins, sepiapterin, and an unidentified presumed pteridine in pr and prbw. Pteridine analyses in double mutants combining pr with one of three other eye color mutants sepia, Henna-recessive3, and prune2, suggest that the metabolic block in pr occurs prior to sepiapterin biosynthesis. Measurements of GTP and GTP cyclohydrolase in pr showed wild-type levels and indicate the metabolic block in pr to be at one of the steps converting dihydroneopterin triphosphate to sepiapterin. Quantitation of pteridines in suppressed purple [su(s)2; pr and pr; su(pr)e3] shows restoration of pteridines to wild-type or nearly wild-type levels.

Aging