meta-Tyrosine in Festuca rubra ssp. commutata (Chewings fescue) is synthesized by hydroxylation of phenylalanine

Metabolization of Free Oxidized Aromatic Amino Acids by Saccharomyces cerevisiae

The aromatic amino acids tryptophan, phenylalanine, and tyrosine are targets for oxidation during food processing. We investigated whether S. cerevisiae can use nonproteinogenic aromatic amino acids as substrates for degradation via the Ehrlich pathway. The metabolic fate of seven amino acids (p-, o-, m-tyrosine, 3,4-dihydroxyphenylalanine (DOPA), 3-nitrotyrosine, 3-chlorotyrosine, and dityrosine) in the presence of S. cerevisiae was assessed. All investigated amino acids except dityrosine were metabolized by yeast. The amino acids 3-nitrotyrosine and o-tyrosine were removed from the medium as fast as p-tyrosine, and m-tyrosine, 3-chlorotyrosine, and DOPA more slowly. In summary, 11 metabolites were identified by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). DOPA, 3-nitrotyrosine, and p-tyrosine were metabolized predominantly to the Ehrlich alcohols, whereas o-tyrosine and m-tyrosine were metabolized predominantly to α-hydroxy acids. Our results indicate that nonproteinogenic aromatic amino acids can be taken up and transaminated by S. cerevisiae quite effectively but that decarboxylation and reduction to Ehrlich alcohols as the final metabolites is hampered by hydroxyl groups in the o- or m-positions of the phenyl ring. The data on amino acid metabolism were substantiated by the analysis of five commercial beer samples, which revealed the presence of hydroxytyrosol (ca. 0.01-0.1 mg/L) in beer for the first time.

Toxicity of meta-Tyrosine

L-Tyrosine (Tyr) is one of the twenty proteinogenic amino acids and also acts as a precursor for secondary metabolites. Tyr is prone to modifications, especially under conditions of cellular redox imbalance. The oxidation of Tyr precursor phenylalanine leads to the formation of Tyr non-proteinogenic isomers, including meta-Tyr (m-Tyr), a marker of oxidative stress. The aim of this review is to summarize the current knowledge on m-Tyr toxicity. The direct m-Tyr mode of action is linked to its incorporation into proteins, resulting in their improper conformation. Furthermore, m-Tyr produced by some plants as an allelochemical impacts the growth and development of neighboring organisms. In plants, the direct harmful effect of m-Tyr is due to its modification of the proteins structure, whereas its indirect action is linked to the disruption of reactive oxygen and nitrogen species metabolism. In humans, the elevated concentration of m-Tyr is characteristic of various diseases and ageing. Indeed, m-Tyr is believed to play an important role in cancer physiology. Thus, since, in animal cells, m-Tyr is formed directly in response to oxidative stress, whereas, in plants, m-Tyr is also synthesized enzymatically and serves as a chemical weapon in plant-plant competition, the general concept of m-Tyr role in living organisms should be specified.

Misincorporation Proteomics Technologies: A Review

Proteinopathies are diseases caused by factors that affect proteoform conformation. As such, a prevalent hypothesis is that the misincorporation of noncanonical amino acids into a proteoform results in detrimental structures. However, this hypothesis is missing proteomic evidence, specifically the detection of a noncanonical amino acid in a peptide sequence. This review aims to outline the current state of technology that can be used to investigate mistranslations and misincorporations whilst framing the pursuit as Misincorporation Proteomics (MiP). The current availability of technologies explored herein is mass spectrometry, sample enrichment/preparation, data analysis techniques, and the hyphenation of approaches. While many of these technologies show potential, our review reveals a need for further development and refinement of approaches is still required.

Peroxynitrite induced signaling pathways in plant response to non-proteinogenic amino acids

Nitro/oxidative modifications of proteins and RNA nitration resulted from altered peroxynitrite generation are elements of the indirect mode of action of canavanine and meta-tyrosine in plants Environmental conditions and stresses, including supplementation with toxic compounds, are known to impair reactive oxygen (ROS) and reactive nitrogen species (RNS) homeostasis, leading to modification in production of oxidized and nitrated derivatives. The role of nitrated and/or oxidized biotargets differs depending on the stress factors and developmental stage of plants. Canavanine (CAN) and meta-tyrosine (m-Tyr) are non-proteinogenic amino acids (NPAAs). CAN, the structural analog of arginine, is found mostly in seeds of Fabaceae species, as a storage form of nitrogen. In mammalian cells, CAN is used as an anticancer agent due to its inhibitory action on nitric oxide synthesis. m-Tyr is a structural analogue of phenylalanine and an allelochemical found in root exudates of fescues. In animals, m-Tyr is recognized as a marker of oxidative stress. Supplementation of plants with CAN or m-Tyr modify ROS and RNS metabolism. Over the last few years of our research, we have collected the complex data on ROS and RNS metabolism in tomato (Solanum lycopersicum L.) plants exposed to CAN or m-Tyr. In addition, we have shown the level of nitrated RNA (8-Nitro-guanine) in roots of seedlings, stressed by the tested NPAAs. In this review, we describe the model of CAN and m-Tyr mode of action in plants based on modifications of signaling pathways induced by ROS/RNS with a special focus on peroxynitrite induced RNA and protein modifications.

Advances and Prospects of Phenolic Acids Production, Biorefinery and Analysis

Biotechnological production of phenolic acids is attracting increased interest due to their superior antioxidant activity, as well as other antimicrobial, dietary, and health benefits. As secondary metabolites, primarily found in plants and fungi, they are effective free radical scavengers due to the phenolic group available in their structure. Therefore, phenolic acids are widely utilised by pharmaceutical, food, cosmetic, and chemical industries. A demand for phenolic acids is mostly satisfied by utilising chemically synthesised compounds, with only a low quantity obtained from natural sources. As an alternative to chemical synthesis, environmentally friendly bio-based technologies are necessary for development in large-scale production. One of the most promising sustainable technologies is the utilisation of microbial cell factories for biosynthesis of phenolic acids. In this paper, we perform a systematic comparison of the best known natural sources of phenolic acids. The advances and prospects in the development of microbial cell factories for biosynthesis of these bioactive compounds are discussed in more detail. A special consideration is given to the modern production methods and analytics of phenolic acids.

The Phytotoxicity of Meta-Tyrosine Is Associated With Altered Phenylalanine Metabolism and Misincorporation of This Non-Proteinogenic Phe-Analog to the Plant's Proteome

Plants produce a myriad of specialized (secondary) metabolites that are highly diverse chemically, and exhibit distinct biological functions. Here, we focus on meta-tyrosine (m-tyrosine), a non-proteinogenic byproduct that is often formed by a direct oxidation of phenylalanine (Phe). Some plant species (e.g., Euphorbia myrsinites and Festuca rubra) produce and accumulate high levels of m-tyrosine in their root-tips via enzymatic pathways. Upon its release to soil, the Phe-analog, m-tyrosine, affects early post-germination development (i.e., altered root development, cotyledon or leaf chlorosis, and retarded growth) of nearby plant life. However, the molecular basis of m-tyrosine-mediated (phyto)toxicity remains, to date, insufficiently understood and are still awaiting their functional characterization. It is anticipated that upon its uptake, m-tyrosine impairs key metabolic processes, or affects essential cellular activities in the plant. Here, we provide evidences that the phytotoxic effects of m-tyrosine involve two distinct molecular pathways. These include reduced steady state levels of several amino acids, and in particularly altered biosynthesis of the phenylalanine (Phe), an essential α-amino acid, which is also required for the folding and activities of proteins. In addition, proteomic studies indicate that m-tyrosine is misincorporated in place of Phe, mainly into the plant organellar proteomes. These data are supported by analyses of adt mutants, which are affected in Phe-metabolism, as well as of var2 mutants, which lack FtsH2, a major component of the chloroplast FtsH proteolytic machinery, which show higher sensitivity to m-tyrosine. Plants treated with m-tyrosine show organellar biogenesis defects, reduced respiration and photosynthetic activities and growth and developmental defect phenotypes.

Phenylalanine roles in the seed-to-seedling stage: Not just an amino acid

Phenylalanine is an aromatic amino acid that provides the carbon skeleton for the phenylpropanoid pathway, making many diverse chemicals used for structure, defense, and yet undiscovered functions. The identification of the arogenate dehydratase (ADT) enzymes in the genetic model Arabidopsis thaliana provided a platform to explore the roles of phenylalanine in all stages of life: germination, in the seed-to-seedling transition stage, organelle function, and in generation of defense mechanisms, enabling further studies in other plants. From the literature, data indicate that phenylalanine produced by ADT may have direct roles in organellar and tissue development. Recent studies implicate ADTs in cell division and protection from Reactive Oxygen Species, and in signaling and growth. Research in phenylalanine and subsequent phenylpropanoids also point to a role of phenylalanine as a purveyor of C and N nutrients. The understanding of phenylalanine action in plant cells is enhanced by recent research on phenylalanine in animal cells.

Phenylalanine meta-Hydroxylase: A Single Residue Mediates Mechanistic Control of Aromatic Amino Acid Hydroxylation

The rare nonproteinogenic amino acid, meta‐l‐tyrosine is biosynthetically intriguing. Whilst the biogenesis of tyrosine from phenylalanine is well characterised, the mechanistic basis for meta‐hydroxylation is unknown. Herein, we report the analysis of 3‐hydroxylase (Phe3H) from Streptomyces coeruleorubidus. Insights from kinetic analyses of the wild‐type enzyme and key mutants as well as of the biocatalytic conversion of synthetic isotopically labelled substrates and fluorinated substrate analogues advance understanding of the process by which meta‐hydroxylation is mediated, revealing T202 to play an important role. In the case of the WT enzyme, a deuterium label at the 3‐position is lost, whereas in in the T202A mutant 75 % retention is observed, with loss of stereospecificity. These data suggest that one of two possible mechanisms is at play; direct, enzyme‐catalysed deprotonation following electrophilic aromatic substitution or stereospecific loss of one proton after a 1,2‐hydride shift. Furthermore, our kinetic parameters for Phe3H show efficient regiospecific generation of meta‐l‐tyrosine from phenylalanine and demonstrate the enzyme's ability to regiospecifically hydroxylate unnatural fluorinated substrates.

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.

Destabilization of ROS metabolism in tomato roots as a phytotoxic effect of meta-tyrosine

meta-Tyrosine (m-Tyr) is a non-protein amino acid produced in both plants and animals. Primary mode of action of this phenylalanine analog is its incorporation into protein structure leading to formation of aberrant molecules. An increased level of m-Tyr in animal cells is detected under oxidative stress and during age-related processes characterized by overproduction of reactive oxygen species (ROS). The aim of this study was to link m-Tyr physiological action to disturbances in ROS metabolism in tomato (Solanum lycopersicum L.) seedlings roots. Treatment of tomato seedlings with m-Tyr (50 or 250 μM) for 24-72 h led to inhibition of root growth without a lethal effect. Toxicity of m-Tyr after 72 h was connected with an increase in hydrogen peroxide concentration in roots and ROS leakage into the surrounding medium. On the contrary, membrane permeability and lipid peroxidation in roots were the same as for the control. This was accompanied by a decrease in total antioxidant activity and an increased accumulation of phenolic compounds. Catalase (CAT) activity declined in roots exposed to 50 μM m-Tyr after 24 h while after 72 h activity of this enzyme was inhibited in both treated and non-treated samples. Activities of different superoxide dismutase (SOD) isoforms were similar in m-Tyr stressed roots and in the control. Prolonged culture resulted in decrease of transcript level of genes coding CAT and SOD with the exception of FeSOD. Moreover, m-Tyr increased the level of protein carbonyl groups indicating induction of oxidative stress as a non-direct mode of action.

meta-Tyrosine induces modification of reactive nitrogen species level, protein nitration and nitrosoglutathione reductase in tomato roots

A non-protein amino acid (NPAA) - meta-Tyrosine (m-Tyr), is a harmful compound produced by fescue roots. Young (3-4 days old) tomato (Solanum lycopersicum L.) seedlings were supplemented for 24-72 h with m-Tyr (50 or 250 μM) inhibiting root growth by 50 or 100%, without lethal effect. Fluorescence of DAF-FM and APF derivatives was determined to show reactive nitrogen species (RNS) localization and level in roots of tomato plants. m-Tyr-induced restriction of root elongation growth was related to formation of nitrated proteins described as content of 3-nitrotyrosine. Supplementation with m-Tyr enhanced superoxide radicals generation in extracts of tomato roots and stimulated protein nitration. It correlated well to increase of fluorescence of DAF-FM derivatives, and transiently stimulated fluorescence of APF derivatives corresponding respectively to NO and ONOO^- formation. Alterations in RNS formation induced by m-Tyr were linked to metabolism of nitrosoglutathione (GSNO). Activity of nitrosoglutatione reductase (GSNOR), catalyzing degradation of GSNO was enhanced by long term plant supplementation with m-Tyr, similarly as protein abundance, while transcripts level were only slightly altered by tested NPAA. We conclude, that although in animal cells m-Tyr is considered as a marker of oxidative stress, its secondary mode of action in tomato plants involves perturbation in RNS formation, alteration in GSNO metabolism and modification of protein nitration level.

Roles of the tyrosine isomers meta-tyrosine and ortho-tyrosine in oxidative stress

The damage to cellular components by reactive oxygen species, termed oxidative stress, both increases with age and likely contributes to age-related diseases including Alzheimer's disease, atherosclerosis, diabetes, and cataract formation. In the setting of oxidative stress, hydroxyl radicals can oxidize the benzyl ring of the amino acid phenylalanine, which then produces the abnormal tyrosine isomers meta-tyrosine or ortho-tyrosine. While elevations in m-tyrosine and o-tyrosine concentrations have been used as a biological marker of oxidative stress, there is emerging evidence from bacterial, plant, and mammalian studies demonstrating that these isomers, particularly m-tyrosine, directly produce adverse effects to cells and tissues. These new findings suggest that the abnormal tyrosine isomers could in fact represent mediators of the effects of oxidative stress. Consequently the accumulation of m- and o-tyrosine may disrupt cellular homeostasis and contribute to disease pathogenesis, and as result, effective defenses against oxidative stress can encompass not only the elimination of reactive oxygen species but also the metabolism and ultimately the removal of the abnormal tyrosine isomers from the cellular amino acid pool. Future research in this area is needed to clarify the biologic mechanisms by which the tyrosine isomers damage cells and disrupt the function of tissues and organs and to identify the metabolic pathways involved in removing the accumulated isomers after exposure to oxidative stress.

Role of Tyrosine Isomers in Acute and Chronic Diseases Leading to Oxidative Stress - A Review

Oxidative stress plays a major role in the pathogenesis of a variety of acute and chronic diseases. Measurement of the oxidative stress-related end products may be performed, e.g. that of structural isomers of the physiological para-tyrosine, namely meta- and ortho-tyrosine, that are oxidized derivatives of phenylalanine. Recent data suggest that in sepsis, serum level of meta-tyrosine increases, which peaks on the 2(nd) and 3(rd) days (p<0.05 vs. controls), and the kinetics follows the intensity of the systemic inflammation correlating with serum procalcitonin levels. In a similar study subset, urinary meta-tyrosine excretion correlated with both need of daily insulin dose and the insulin-glucose product in non-diabetic septic cases (p<0.01 for both). Using linear regression model, meta-tyrosine excretion, urinary meta-tyrosine/para-tyrosine, urinary ortho-tyrosine/para-tyrosine and urinary (meta- + orthotyrosine)/ para-tyrosine proved to be markers of carbohydrate homeostasis. In a chronic rodent model, we tried to compensate the abnormal tyrosine isomers using para-tyrosine, the physiological amino acid. Rats were fed a standard high cholesterol-diet, and were given para-tyrosine or vehicle orally. High-cholesterol feeding lead to a significant increase in aortic wall meta-tyrosine content and a decreased vasorelaxation of the aorta to insulin and the glucagon-like peptide-1 analogue, liraglutide, that both could be prevented by administration of para-tyrosine. Concluding, these data suggest that meta- and ortho-tyrosine are potential markers of oxidative stress in acute diseases related to oxidative stress, and may also interfere with insulin action in septic humans. Competition of meta- and ortho-tyrosine by supplementation of para-tyrosine may exert a protective role in oxidative stress-related diseases.

New Umami Amides: Structure-Taste Relationship Studies of Cinnamic Acid Derived Amides and the Natural Occurrence of an Intense Umami Amide in Zanthoxylum piperitum

A series of aromatic amides were synthesized from various acids and amines selected from naturally occurring structural frameworks. These synthetic amides were evaluated for umami taste in comparison with monosodium glutamate. The effect of the substitution pattern of both the acid and the amine parts on umami taste was investigated. The only intensely umami-tasting amides were those made from 3,4-dimethoxycinnamic acid. The amine part was more tolerant to structural changes. Amides bearing an alkyl- or alkoxy-substituted phenylethylamine residue displayed a clean umami taste as 20 ppm solutions in water. Ultraperformance liquid chromatography coupled with a high quadrupole-Orbitrap mass spectrometer (UPLC/MS) was subsequently used to show the natural occurrence of these amides. (E)-3-(3,4-Dimethoxyphenyl)-N-(4-methoxyphenethyl)acrylamide was shown to occur in the roots and stems of Zanthoxylum piperitum, a plant of the family Rutaceae growing in Korea, Japan, and China.

Conformational and vibrational analyses of meta-tyrosine: An experimental and theoretical study

M-tyrosine is one kind of positional isomer of tyrosine which is widely applied in agrichemical, medicinal chemistry, and food science. However, the structural and vibrational features of m-tyrosine have not been reported or systematically investigated. In this work, potential energy surface (PES) calculations were used for searching and determining the stable zwitterionic conformers of m-tyrosine, and the Raman spectra of m-tyrosine and deuterated m-tyrosine were measured and interpreted based on theoretical computation. For the spectral simulation, several DFT-based quantum chemistry (QC) methods were employed, and the M06-2X functional with SMD solvent model was found to be best in reproducing the Raman spectra and geometrical property. As such, this study has not only presented a detailed study of m-tyrosine's vibrational property which is lack in the literature, but also may shed some light on the optimal choice of QC methods for calculation of conformations and vibrational properties of zwitterionic amino acids.

Synthesis and evaluation as biodegradable herbicides of halogenated analogs of L-meta-tyrosine

L-meta-tyrosine is an herbicidal nonprotein amino acid isolated some years ago from fine fescue grasses and characterized by its almost immediate microbial degradation in soil (half-life <24 h). Nine monohalogenated or dihalogenated analogs of this allelochemical have been obtained through a seven-step stereoselective synthesis from commercial halogenated phenols. Bioassays showed a large range of biological responses, from a growth root inhibition of lettuce seedling similar to that noted with m-tyrosine [2-amino-3-(2-chloro-5-hydroxyphenyl)propanoic acid or compound 8b] to an increase of the primary root growth concomitant with a delay of secondary root initiation [2-amino-3-[2-fluoro-5-hydroxy-3-(trifluoromethyl)phenyl]propanoic acid or compound 8h]. Compound 8b was slightly less degraded than m-tyrosine in the nonsterilized nutritive solution used for lettuce development, while the concentration of compound 8h remained unchanged for at least 2 weeks. These data indicate that it is possible to manipulate both biological properties and degradation of m-tyrosine by halogen addition.

Biodegradation of the allelopathic chemical m-tyrosine by Bacillus aquimaris SSC5 involves the homogentisate central pathway

m-Tyrosine is an amino acid analogue, exuded from the roots of fescue grasses, which acts as a potent allelopathic and a broad spectrum herbicidal chemical. Although the production and toxic effects of m-tyrosine are known, its microbial degradation has not been documented yet. A soil microcosm study showed efficient degradation of m-tyrosine by the inhabitant microorganisms. A bacterial strain designated SSC5, that was able to utilize m-tyrosine as the sole source of carbon, nitrogen, and energy, was isolated from the soil microcosm and was characterized as Bacillus aquimaris. Analytical methods such as HPLC, GC-MS, and ¹H-NMR performed on the resting cell samples identified the formation of 3-hydroxyphenylpyruvate (3-OH-PPA), 3-hydroxyphenylacetate (3-OH-PhAc), and homogentisate (HMG) as major intermediates in the m-tyrosine degradation pathway. Enzymatic assays carried out on cell-free lysates of m-tyrosine-induced cells confirmed transamination reaction as the first step of m-tyrosine degradation. The intermediate 3-OH-PhAc thus obtained was further funneled into the HMG central pathway as revealed by a hydroxylase enzyme assay. Subsequent degradation of HMG occurred by ring cleavage catalyzed by the enzyme homogentisate 1, 2-dioxygenase. This study has significant implications in terms of understanding the environmental fate of m-tyrosine as well as regulation of its phytotoxic effect by soil microorganisms.

Amino acids in the rhizosphere: from plants to microbes

Often referred to as the "building blocks of proteins", the 20 canonical proteinogenic amino acids are ubiquitous in biological systems as the functional units in proteins. Sometimes overlooked are their varying additional roles that include serving as metabolic intermediaries, playing structural roles in bioactive natural products, acting as cosubstrates in enzymatic transformations, and as key regulators of cellular physiology. Amino acids can also serve as biological sources of both carbon and nitrogen and are found in the rhizosphere as a result of lysis or cellular efflux from plants and microbes and proteolysis of existing peptides. While both plants and microbes apparently prefer to take up nitrogen in its inorganic form, their ability to take up and use amino acids may confer a selective advantage in certain environments where organic nitrogen is abundant. Further, certain amino acids (e.g., glutamate and proline) and their betaines (e.g., glycine betaine) serve as compatible solutes necessary for osmoregulation in plants and microbes and can undergo rapid cellular flux. This ability is of particular importance in an ecological niche such as the rhizosphere, which is prone to significant variations in solute concentrations. Amino acids are also shown to alter key phenotypes related to plant root growth and microbial colonization, symbiotic interactions, and pathogenesis in the rhizosphere. This review will focus on the sources, transport mechanisms, and potential roles of the 20 canonical proteinogenic amino acids in the rhizosphere.