Purification and characterisation of tyrosine decarboxylase and aromatic-L-amino-acid decarboxylase

Discovery and inhibition of an interspecies gut bacterial pathway for Levodopa metabolism

The human gut microbiota metabolizes the Parkinson’s disease medication Levodopa (L-dopa), potentially reducing drug availability and causing side effects. However, the organisms, genes, and enzymes responsible for this activity in patients and their susceptibility to inhibition by host-targeted drugs are unknown. Here, we describe an interspecies pathway for gut bacterial L-dopa metabolism. Conversion of L-dopa to dopamine by a pyridoxal phosphate-dependent tyrosine decarboxylase from Enterococcus faecalis is followed by transformation of dopamine to m-tyramine by a molybdenum-dependent dehydroxylase from Eggerthella lenta. These enzymes predict drug metabolism in complex human gut microbiotas. Although a drug that targets host aromatic amino acid decarboxylase does not prevent gut microbial L-dopa decarboxylation, we identified a compound that inhibits this activity in Parkinson’s patient microbiotas and increases L-dopa bioavailability in mice.

Improving Soluble Expression of Tyrosine Decarboxylase from Lactobacillus brevis for Tyramine Synthesis with High Total Turnover Number

The soluble expression of tyrosine decarboxylase (TDC) in heterologous host is often challenging. Here, acidic condition was found to be favorable for improving the soluble expression of TDC from Lactobacillus brevis in Escherichia coli, while addition of carbohydrates (such as glucose, arabinose, and fructose) was vital for decreasing the insoluble fraction. By simple pH control and addition of glucose, the specific activity of TDC in crude extract was enhanced to 46.3 U mg^-1, 3.67-fold of that produced from LB medium. Optimization of the reaction conditions revealed that Tween-80 was effective in improving the tyramine production catalyzed by TDC, especially at high tyrosine loadings. As much as 400 mM tyrosine could be completely converted into tyramine with a substrate to catalyst ratio of 29.0 g g^-1 and total turnover number of 23,300. This study provides efficient strategies for the highly soluble expression of TDC and biocatalytic production of tyramine.

Biocatalytic approaches towards the stereoselective synthesis of vicinal amino alcohols

The global need for clean manufacturing technologies and the management of hazardous chemicals and waste present new research challenges to both chemistry and biotechnology.

Crystal structure of tyrosine decarboxylase and identification of key residues involved in conformational swing and substrate binding

Tyrosine decarboxylase (TDC) is a pyridoxal 5-phosphate (PLP)-dependent enzyme and is mainly responsible for the synthesis of tyramine, an important biogenic amine. In this study, the crystal structures of the apo and holo forms of Lactobacillus brevis TDC (LbTDC) were determined. The LbTDC displays only 25% sequence identity with the only reported TDC structure. Site-directed mutagenesis of the conformationally flexible sites and catalytic center was performed to investigate the potential catalytic mechanism. It was found that H241 in the active site plays an important role in PLP binding because it has different conformations in the apo and holo structures of LbTDC. After binding to PLP, H241 rotated to the position adjacent to the PLP pyridine ring. Alanine scanning mutagenesis revealed several crucial regions that determine the substrate specificity and catalytic activity. Among the mutants, the S586A variant displayed increased catalytic efficiency and substrate affinity, which is attributed to decreased steric hindrance and increased hydrophobicity, as verified by the saturation mutagenesis at S586. Our results provide structural information about the residues important for the protein engineering of TDC to improve catalytic efficiency in the green manufacturing of tyramine.

Reducing biogenic-amine-producing bacteria, decarboxylase activity, and biogenic amines in raw milk cheese by high-pressure treatments

Biogenic amines may reach concentrations of public health concern in some cheeses. To minimize biogenic amine buildup in raw milk cheese, high-pressure treatments of 400 or 600 MPa for 5 min were applied on days 21 and 35 of ripening. On day 60, counts of lactic acid bacteria, enterococci, and lactobacilli were 1 to 2 log units lower in cheeses treated at 400 MPa and 4 to 6 log units lower in cheeses treated at 600 MPa than in control cheese. At that time, aminopeptidase activity was 16 to 75% lower in cheeses treated at 400 MPa and 56 to 81% lower in cheeses treated at 600 MPa than in control cheese, while the total free amino acid concentration was 35 to 53% higher in cheeses treated at 400 MPa and 3 to 15% higher in cheeses treated at 600 MPa, and decarboxylase activity was 86 to 96% lower in cheeses treated at 400 MPa and 93 to 100% lower in cheeses treated at 600 MPa. Tyramine, putrescine, and cadaverine were the most abundant amines in control cheese. The total biogenic amine concentration on day 60, which reached a maximum of 1.089 mg/g dry matter in control cheese, was 27 to 33% lower in cheeses treated at 400 MPa and 40 to 65% lower in cheeses treated at 600 MPa. On day 240, total biogenic amines attained a concentration of 3.690 mg/g dry matter in control cheese and contents 11 to 45% lower in cheeses treated at 400 MPa and 73 to 76% lower in cheeses treated at 600 MPa. Over 80% of the histidine and 95% of the tyrosine had been converted into histamine and tyramine in control cheese by day 60. Substrate depletion played an important role in the rate of biogenic amine buildup, becoming a limiting factor in the case of some amino acids.

Tyramine and phenylethylamine biosynthesis by food bacteria

Tyramine poisoning is caused by the ingestion of food containing high levels of tyramine, a biogenic amine. Any foods containing free tyrosine are subject to tyramine formation if poor sanitation and low quality foods are used or if the food is subject to temperature abuse or extended storage time. Tyramine is generated by decarboxylation of the tyrosine through tyrosine decarboxylase (TDC) enzymes derived from the bacteria present in the food. Bacterial TDC have been only unequivocally identified and characterized in Gram-positive bacteria, especially in lactic acid bacteria. Pyridoxal phosphate (PLP)-dependent TDC encoding genes (tyrDC) appeared flanked by a similar genetic organization in several species of lactic acid bacteria, suggesting a common origin by a single mobile genetic element. Bacterial TDC are also able to decarboxylate phenylalanine to produce phenylethylamine (PEA), another biogenic amine. The molecular knowledge of the genes involved in tyramine production has led to the development of molecular methods for the detection of bacteria able to produce tyramine and PEA. These rapid and simple methods could be used for the analysis of the ability to form tyramine by bacteria in order to evaluate the potential risk of tyramine biosynthesis in food products.

First evidence of a membrane-bound, tyramine and beta-phenylethylamine producing, tyrosine decarboxylase in Enterococcus faecalis: a two-dimensional electrophoresis proteomic study

The soluble and membrane proteome of a tyramine producing Enterococcus faecalis, isolated from an Italian goat cheese, was investigated. A detailed analysis revealed that this strain also produces small amounts of beta-phenylethylamine. Kinetics of tyramine and beta-phenylethylamine accumulation, evaluated in tyrosine plus phenylalanine-enriched cultures (stimulated condition), suggest that the same enzyme, the tyrosine decarboxylase (TDC), catalyzes both tyrosine and phenylalanine decarboxylation: tyrosine was recognized as the first substrate and completely converted into tyramine (100% yield) while phenylalanine was decarboxylated to beta-phenylethylamine (10% yield) only when tyrosine was completely depleted. The presence of an aspecific aromatic amino acid decarboxylase is a common feature in eukaryotes, but in bacteria only indirect evidences of a phenylalanine decarboxylating TDC have been presented so far. Comparative proteomic investigations, performed by 2-DE and MALDI-TOF/TOF MS, on bacteria grown in conditions stimulating tyramine and beta-phenylethylamine biosynthesis and in control conditions revealed 49 differentially expressed proteins. Except for aromatic amino acid biosynthetic enzymes, no significant down-regulation of the central metabolic pathways was observed in stimulated conditions, suggesting that tyrosine decarboxylation does not compete with the other energy-supplying routes. The most interesting finding is a membrane-bound TDC highly over-expressed during amine production. This is the first evidence of a true membrane-bound TDC, longly suspected in bacteria on the basis of the gene sequence.

De-racemization of enantiomers versus de-epimerization of diastereomers--classification of dynamic kinetic asymmetric transformations (DYKAT)

The isolation of single stereoisomers from a racemic (or diastereomeric) mixture by enzymatic or chemical resolution techniques goes in hand with the disposal of 50% (racemate) or more (diastereomeric mixtures) of the "undesired" substrate isomer(s). In order to circumvent this drawback, dynamic systems have been developed for the de-racemization of enantiomers and the de-epimerizations of diastereomers. Key strategies within this area are discussed and are classified according to their underlying kinetics, that is, dynamic kinetic resolution (DKR), dynamic kinetic asymmetric transformations (DYKAT), and hybrids between both of them. Finally, two novel types of DYKAT are defined.

Amino Acid Catabolic Pathways of Lactic Acid Bacteria

Lactic acid bacteria (LAB) constitute a diverse group of Gram positive obligately fermentative microorganisms which include both beneficial and pathogenic strains. LAB generally have complex nutritional requirements and therefore they are usually associated with nutrient-rich environments such as animal bodies, plants and foodstuffs. Amino acids represent an important resource for LAB and their utilization serves a number of physiological roles such as intracellular pH control, generation of metabolic energy or redox power, and resistance to stress. As a consequence, the regulation of amino acid catabolism involves a wide set of both general and specific regulators and shows significant differences among LAB. Moreover, due to their fermentative metabolism, LAB amino acid catabolic pathways in some cases differ significantly from those described in best studied prokaryotic model organisms such as Escherichia coli or Bacillus subtilis. Thus, LAB amino acid catabolism constitutes an interesting case for the study of metabolic pathways. Furthermore, LAB are involved in the production of a great variety of fermented products so that the products of amino acid catabolism are also relevant for the safety and the quality of fermented products.

Tyramine and phenylethylamine production among lactic acid bacteria isolated from wine

The ability of wine lactic acid bacteria to produce tyramine and phenylethylamine was investigated by biochemical and genetic methods. An easy and accurate plate medium was developed to detect tyramine-producer strains, and a specific PCR assay that detects the presence of tdc gene was employed. All strains possessing the tdc gene were shown to produce tyramine and phenylethylamine. Wines containing high quantities of tyramine and phenylethylamine were found to contain Lactobacillus brevis or Lactobacillus hilgardii. The main tyramine producer was L. brevis. The ability to produce tyramine was absent or infrequent in the rest of the analysed wine species.

First genetic characterization of a bacterial β-phenylethylamine biosynthetic enzyme in Enterococcus faecium RM58

Enterococcus faecium RM58 produces beta-phenylethylamine and tyramine. A gene from Ent. faecium RM58 coding for a 625 amino-acid residues protein that shows 85% identity to Enterococcus faecalis tyrosine decarboxylase has been expressed in Escherichia coli, resulting in L-phenylalanine and L-tyrosine decarboxylase activities. Both activities were lost when a truncated protein lacking 84 amino acids at its C-terminus was expressed in E. coli. This study constitutes the first genetic characterization of a bacterial protein having L-phenylalanine decarboxylase activity and solves a long-standing question regarding the specificity of tyrosine decarboxylases in enterococci.

Production of biogenic amines by lactic acid bacteria: screening by PCR, thin-layer chromatography, and high-performance liquid chromatography of strains isolated from wine and must

Biogenic amines are frequently found in wine and other fermented food. We investigated the ability of 133 strains of lactic acid bacteria isolated from musts and wines of different origins to produce histamine, tyramine, and putrescine. We detected the genes responsible for encoding the corresponding amino acid decarboxylases through PCR assays using two primer sets for every gene: histidine decarboxylase (hdc), tyrosine decarboxylase (tdc), and ornithine decarboxylase (odc); these primers were taken from the literature or designed by us. Only one strain of Lactobacillus hilgardii was shown to possess the hdc gene, whereas four strains of Lactobacillus brevis had the tdc gene. None of the Oenococcus oeni strains, the main agents of malolactic fermentation, was a biogenic amine producer. All PCR amplicon band-positive results were confirmed by thin-layer chromatography and high-performance liquid chromatography analyses.

Sequencing of the tyrosine decarboxylase cluster of Lactococcus lactis IPLA 655 and the development of a PCR method for detecting tyrosine decarboxylating lactic acid bacteria

The enzymatic decarboxylation of tyrosine produces tyramine, the most abundant biogenic amine in dairy products-especially in cheeses. The screening of lactic acid bacteria isolated from different artisanal cheeses and a number of microbial collections identified 22 tyramine-producing strains belonging to different genera. The Lactococcus lactis strain IPLA 655 was selected, and the genes encoding a putative tyrosyl tRNA synthetase, a tyrosine decarboxylase (tdcA), and a tyrosine-tyramine antiporter, found together as a cluster, were sequenced. The disruption of tdcA yielded a strain unable to produce tyramine. Comparison of the L. lactis IPLA 655 tdcA gene with database tdcA sequences led to the design of two primers for use in a PCR method that identified potential tyramine-producing strains. The proposed method can use purified DNA, isolated colonies, milk, curd, and even cheese as a template. Molecular tools for the rapid detection of tyramine-producing bacteria at any time during the fermentation process could help prevent tyramine accumulation in fermented foods. The proposed technique could be of great use to the food industry.

The tyrosine decarboxylase operon of Lactobacillus brevis IOEB 9809: characterization and conservation in tyramine-producing bacteria

Bacterial genes of tyrosine decarboxylases were recently identified. Here we continued the sequencing of the tyrosine decarboxylase locus of Lactobacillus brevis IOEB 9809 and determined a total of 7979 bp. The sequence contained four complete genes encoding a tyrosyl-tRNA synthetase, the tyrosine decarboxylase, a probable tyrosine permease and a Na+/H+ antiporter. Rapid amplification of cDNA ends (RACE) was employed to determine the 5'-end of mRNAs containing the tyrosine decarboxylase gene. It was located only 34-35 nucleotides upstream of the start codon, suggesting that the preceding tyrosyl-tRNA synthetase gene was transcribed separately. In contrast, reverse transcription-polymerase chain reactions (RT-PCRs) carried out with primers designed to amplify regions spanning gene junctions showed that some mRNAs contained the four genes. Homology searches revealed similar clusters of four genes in the genome sequences of Enterococcus faecalis and Enterococcus faecium. Phylogenetic analyses supported the hypothesis that these genes evolved all together. These data suggest that bacterial tyrosine decarboxylases are encoded in an operon containing four genes.

Preliminary characterization of beta-decarboxylase activities in Staphylococcus carnosus 833, a strain used in sausage fermentation

In sausage, Staphylococcus carnosus increases the levels of methyl ketones which could arise from incomplete beta-oxidation of fatty acids followed by a decarboxylation. The objective of this work was to characterize the beta-decarboxylase activities in cell-free extract. By using different substrates, at least two kinds of beta-decarboxylase activities were shown: an acetoacetate-like and an oxaloacetate-like. The first one leads to the production of ketones from ethylbutyryl acetate or acetoacetic acid. The activity was optimal at pH 6.0, stimulated by pyridoxal phosphate but ethylenediamine tetraacetic acid (EDTA), NaCl, iodoacetate and curing additives were inhibitory. The second decarboxylase activity leads to the production of pyruvic acid from oxaloacetic acid. This activity was optimal at pH 5.0 and stimulated by divalent ions and biotin.

Identification of the Enterococcus faecalis tyrosine decarboxylase operon involved in tyramine production

Screening of a library of Enterococcus faecalis insertional mutants allowed isolation of a mutant affected in tyramine production. The growth of this mutant was similar to that of the wild-type E. faecalis JH2-2 strain in Maijala broth, whereas high-performance liquid chromatography analyses showed that tyramine production, which reached 1,000 microg ml(-1) for the wild-type strain, was completely abolished. Genetic analysis of the insertion locus revealed a gene encoding a decarboxylase with similarity to eukaryotic tyrosine decarboxylases. Sequence analysis revealed a pyridoxal phosphate binding site, indicating that this enzyme belongs to the family of amino acid decarboxylases using this cofactor. Reverse transcription-PCR analyses demonstrated that the gene (tdc) encoding the putative tyrosine decarboxylase of E. faecalis JH2-2 is cotranscribed with the downstream gene encoding a putative tyrosine-tyramine antiporter and with the upstream tyrosyl-tRNA synthetase gene. This study is the first description of a tyrosine decarboxylase gene in prokaryotes.

Purification and partial gene sequence of the tyrosine decarboxylase of Lactobacillus brevis IOEB 9809

Some lactic acid bacteria contain a tyrosine decarboxylase (TDC) which converts tyrosine to tyramine, a biogenic amine frequently encountered in fermented food and wine. Purification and microsequencing of the TDC of Lactobacillus brevis IOEB 9809 allowed us to determine a partial sequence of the TDC gene encoding 264 amino acids of the enzyme. Analysis of this protein sequence revealed typical features of pyridoxal phosphate-dependent amino acid decarboxylases while not any known decarboxylase was closely related to the TDC of L. brevis IOEB 9809. In addition, we could detect other L. brevis strains carrying a TDC gene in a rapid assay based on the polymerase chain reaction.

Purification and characterization of tyrosine decarboxylase of Lactobacillus brevis IOEB 9809 isolated from wine

Tyrosine decarboxylase (EC 4.1.1.25) (TDC) from the wine Lactobacillus brevis IOEB 9809 was purified by a rapid procedure involving anion exchange chromatography, ultrafiltration and hydrophobic interaction chromatography. The protein comprised two subunits of identical molecular mass (approximately 70000 Da). Enzyme activity was dependent on exogenously supplied pyridoxal 5'-phosphate and the enzyme was stable at 4 degrees C in the presence of the coenzyme. Optimum pH for the pure enzyme was 5.0. At this pH, TDC exhibited Michaelis-Menten kinetics (K(m) 0.63 mM, V(max) 998 units) and was highly substrate-specific for L-tyrosine. Other amino acids and L-DOPA are not converted by the protein. Tyramine acted as a mixed non-competitive inhibitor. Significant similarities in some biochemical properties were observed with the corresponding decarboxylase enzyme of Streptococcus faecalis, the sole bacterial TDC described to date.

Tyrosine decarboxylase activity of Lactobacillus brevis IOEB 9809 isolated from wine and L. brevis ATCC 367

Tyramine, a frequent amine in wines, is produced from tyrosine by the tyrosine decarboxylase (TDC) activity of bacteria. The tyramine-producing strain Lactobacillus brevis IOEB 9809 isolated from wine and the reference strain L. brevis ATCC 367 were studied. At the optimum pH, 5.0, K(m) values of IOEB 9809 and ATCC 367 crude extracts for L-tyrosine were 0.58 mM and 0.67 mM, and V(max) was higher for the wine strain (115 U) than the ATCC 367 (66 U). TDC exhibited a preference for L-tyrosine over L-DOPA as substrate. Enzyme activity was pyridoxal-5'-phosphate (PLP)-dependent and it was stabilized by the substrate and coenzyme. In contrast, glycerol and beta-mercaptoethanol strongly inhibited TDC. Tyramine competitively inhibited TDC for both strains. Citric acid, lactic acid and ethanol had an inhibitory effect on cells and crude extracts, but none could inhibit TDC at the usual concentrations in wines.