Regulation of phenylalanine ammonia lyase in Rhodotorula glutinis

Rhodotorula mucilaginosa-alternative sources of natural carotenoids, lipids, and enzymes for industrial use

Biotechnologically useful yeast strains have been receiving important attention worldwide for the demand of a wide range of industries. Rhodotorula mucilaginosa is recognized as a biotechnologically important yeast that has gained great interest as a promising platform strain, owing to the diverse substrate appetites, robust stress resistance, and other gratifying features. Due to its attractive properties, R. mucilaginosa has been regarded as an excellent candidate for the biorefinery of carotenoids, lipids, enzymes, and other functional bioproducts by utilizing low-cost agricultural waste materials as substrates. These compounds have aroused great interest as the potential alternative sources of health-promoting food products, substrates for so-called third-generation biodiesel, and dyes or functional ingredients for cosmetics. Furthermore, the use of R. mucilaginosa has rapidly increased as a result of advancements in fermentation for enhanced production of these valuable bioactive compounds. This review focuses on R. mucilaginosa in these advancements and summarizes its potential prospects as alternative sources of natural bioproducts.

Descriptive and hedonic analyses of low-Phe food formulations containing corn (Zea mays) seedling roots: toward development of a dietary supplement for individuals with phenylketonuria

BACKGROUND

Seedling roots of anthocyanin-rich corn (Zea mays) cultivars contain high levels of phenylalanine ammonia lyase (PAL) activity. The development of a natural dietary supplement containing corn roots could provide the means to improve the restrictive diet of phenylketonuria (PKU) patients by increasing their tolerance to dietary phenylalanine (Phe). Therefore this research was undertaken to explore the sensory characteristics of roots of four corn cultivars as well as to develop and evaluate food products (cereal bar, beverage, jam-like spread) to which roots had been added.

RESULTS

Sensory profiles of corn roots were investigated using ten trained judges. Roots of Japanese Striped corn seedlings were more bitter, pungent and astringent than those of white and yellow cultivars, while roots from the Blue Jade cultivar had a more pronounced earthy/mushroom aroma. Consumer research using 24 untrained panelists provided hedonic (degree-of-liking) assessments for products with and without roots (controls). The former had lower mean scores than the controls; however, the cereal bar had scores above 5 on the nine-point scale for all hedonic assessments compared with the other treated products.

CONCLUSION

By evaluating low-Phe food products containing corn roots, this research ascertained that the root-containing low-Phe cereal bar was an acceptable 'natural' dietary supplement for PKU-affected individuals.

Phenylalanine ammonia-lyase, a key component used for phenylpropanoids production by metabolic engineering

Phenylalanine ammonia-lyase, a versatile enzyme with industrial and medical applications.

Preservation of high phenylalanine ammonia lyase activities in roots of Japanese Striped corn: a potential oral therapeutic to treat phenylketonuria

Phenylketonuria (PKU) is an inherited metabolic disorder caused by deficient phenylalanine hydroxylase (PAH) activity, the enzyme responsible for the disposal of excess amounts of the essential amino acid phenylalanine (Phe). Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) has potential to serve as an enzyme substitution therapy for this human genetic disease. Using 7-day-old Japanese Striped corn seedlings (Japonica Striped maize, Zea mays L. cv. japonica) that contain high activities of PAL, we investigated a number of methods to preserve the roots as an intact food and for long-term storage. The cryoprotectant effects of maple syrup and other edible sugars (mono- and oligosaccharides) were evaluated. Following thawing, the preserved roots were then examined to determine whether the rigid plant cell walls could protect the PAL enzyme from proteolysis during simulated (in vitro) digestion comprised of gastric and intestinal phases. While several treatments led to retention of PAL activity during freezing, upon thawing and in vitro digestion, root tissues that had been previously frozen in the presence of maple syrup exhibited the highest residual PAL activities (∼50% of the initial enzyme activity), in marked contrast to all of the treatments using other edible sugars. The structural integrity of the root cells, and the stability of the functional PAL tetramer were also preserved with the maple syrup protocol. These results have significance for the formulation of oral enzyme/protein therapeutics. When plant tissues are adequately preserved, the rigid cell walls constitute a protective barrier even under harsh (e.g. gastrointestinal-like) conditions.

Biosynthesis and cellular localization of functional polyketides in the gastropod mollusc Scaphander lignarius

Opisthobranchs belong to a subclass of highly evolved and specialised marine gastropods that rely on the use of secondary metabolites for their survival. Here we report the full elucidation of the biosynthesis of aromatic metabolites, lignarenones, in one of these gastropods, the cephalaspidean Scaphander lignarius. Feeding experiments with ²H- and ¹³C-labelled precursors revealed a mixed acetate/propionate polyketide pathway primed by benzoic acid. Phenylalanine ammonia lyase (PAL), unprecedented in animals, is central to the synthesis of this aromatic precursor by oxidative deamination of L-phenylalanine to cinnamic acid. Lignarenones are synthesised in the cytoplasm of specialised eukaryotic cells named Blochmann's glands, which are distributed in biosynthetic tissue localised in the vulnerable mantle of the mollusc. This result supports the hypothesis that this lineage of gastropods has acquired the genetic information to produce the chemical substances that they use for their survival.

What we know that could influence future treatment of phenylketonuria

Phenylketonuria (PKU), a Mendelian autosomal recessive phenotype (OMIM 261600), is an inborn error of metabolism that can result in impaired postnatal cognitive development. The phenotypic outcome is multifactorial in origin, based both in nature, the mutations in the gene encoding the L-phenylalanine hydroxylase enzyme, and nurture, the nutritional experience introducing L-phenylalanine into the diet. The PKU story contains many messages including a framework to appreciate the complexity of this disease where phenotype reflects both locus-specific and genomic components. This knowledge is now being applied in the development of patient-specific therapies.

Preclinical evaluation of multiple species of PEGylated recombinant phenylalanine ammonia lyase for the treatment of phenylketonuria

Phenylketonuria (PKU) is a metabolic disorder, in which loss of phenylalanine hydroxylase activity results in neurotoxic levels of phenylalanine. We used the Pah(enu2/enu2) PKU mouse model in short- and long-term studies of enzyme substitution therapy with PEGylated phenylalanine ammonia lyase (PEG-PAL conjugates) from 4 different species. The most therapeutically effective PAL (Av, Anabaena variabilis) species was one without the highest specific activity, but with the highest stability; indicating the importance of protein stability in the development of effective protein therapeutics. A PEG-Av-p.C503S/p.C565S-PAL effectively lowered phenylalanine levels in both vascular space and brain tissue over a >90 day trial period, resulting in reduced manifestations associated with PKU, including reversal of PKU-associated hypopigmentation and enhanced animal health. Phenylalanine reduction occurred in a dose- and loading-dependent manner, and PEGylation reduced the neutralizing immune response to the enzyme. Human clinical trials with PEG-Av-p.C503S/p.C565S-PAL as a treatment for PKU are underway.

First biosynthetic evidence on the phenyl-containing polyketides of the marine mollusc Scaphander lignarius

The biosynthesis of lignarenones 1 and 2, the major polyketides of the Mediterranean mollusc Scaphander lignarius is described. The process is primed by benzoic acid and requires acetate and propionate as extender units. The labeling pattern suggests PKS-like synthesis of an unusual E,Z,E-triene chain and origin of the benzoate unit from phenylalanine. 13C-13C NMR COSY has been used to establish the labeling positions due to incorporation of 13C2-acetate.

Development of a Combined Biological and Chemical Process for Production of Industrial Aromatics from Renewable Resources

Production of industrial aromatic chemicals from renewable resources could provide a competitive alternative to traditional chemical synthesis routes. This review describes the engineering of microorganisms for the production of p-hydroxycinnamic acid (pHCA) and p-hydroxystyrene (pHS) from glucose. The initial process concept was demonstrated using a tyrosine-producing Escherichia coli strain that overexpressed both fungal phenylalanine/tyrosine ammonia lyase (PAL) and bacterial pHCA decarboxylase (pdc) genes. Further development of this bioprocess resulted in uncoupling the pHCA and pHS production steps to mitigate their toxicity to the production host. The final process consists of a fermentation step to convert glucose to tyrosine using a tyrosine-overproducing E. coli strain. This step is followed by a single biotransformation reaction to deaminate tyrosine to pHCA through immobilized E. coli cells that overexpress the Rhodotorula glutinis PAL gene. Finally, chemical decarboxylation of pHCA produces pHS. This multifaceted approach, which integrates biology, chemistry, and engineering, has allowed development of an economical process at scales suitable for industrial applications.

Phenylalanine ammonia lyase, enzyme substitution therapy for phenylketonuria, where are we now?

Phenylketonuria (PKU) is an autosomal recessive genetic disorder in which mutations in the phenylalanine-4-hydroxylase (PAH) gene result in an inactive enzyme (PAH, EC 1.14.16.1). The effect is an inability to metabolize phenylalanine (Phe), translating into elevated levels of Phe in the bloodstream (hyperphenylalaninemia). If therapy is not implemented at birth, mental retardation can occur. PKU patients respond to treatment with a low-phenylalanine diet, but compliance with the diet is difficult, therefore the development of alternative treatments is desirable. Enzyme substitution therapy with a recombinant phenylalanine ammonia lyase (PAL) is currently being explored. This enzyme converts Phe to the harmless metabolites, trans-cinnamic acid and trace ammonia. Taken orally and when non-absorbable and protected, PAL lowers plasma Phe in mutant hyperphenylalaninemic mouse models. Subcutaneous administration of PAL results in more substantial lowering of plasma and significant reduction in brain Phe levels, however the metabolic effect is not sustained following repeated injections due to an immune response. We have chemically modified PAL by pegylation to produce a protected form of PAL that possesses better specific activity, prolonged half-life, and reduced immunogenicity in vivo. Subcutaneous administration of pegylated molecules to PKU mice has the desired metabolic response (prolonged reduction in blood Phe levels) with greatly attenuated immunogenicity.

Production of l -Phenylalanine from Starch by Analog-Resistant Mutants of Bacillus polymyxa

p -Fluorophenylalanine-resistant mutants of starch-degrading Bacillus polymyxa ATCC 842, generated by ethyl methanesulfonate mutagenesis followed by incubation with caffeine, overproduced small amounts of l -phenylalanine ( l -phe) from starch. A β-2-thienylalanine-resistant mutant (BT R -7) derived from p -fluorophenylalanine mutant (C-4000 FP R -4) and resistant to both p -fluorophenylalanine and β-2-thienylalanine produced 0.5 g of l -phe and 0.15 g of l -tyrosine per liter from 10 g of starch per liter when growing in a minimal medium. trans -Cinnamic acid (CA) was also excreted by both mutants, indicating the possibility of l -phenylalanine ammonia-lyase-induced deamination of l -phe to CA. The amount of l -phe-derived CA detected in BT R -7 was less compared with mutant C-4000 FP R -4. CA production was induced in the parent only when l -phe was used as a sole nitrogen source. Time of CA production in the two mutants could be delayed by addition of other nitrogen sources, an indication of possible l -phenylalanine ammonia-lyase inhibition or repression. The presence of l -phenylalanine ammonia-lyase in B. polymyxa mutant C-4000 FP R -4 was confirmed by assays of cell-free extracts from cells grown in starch minimal medium containing l -phe as the sole nitrogen source. Preliminary studies of the regulation of deoxy- d -arabino-heptulosonate-7-phosphate synthase and prephenate dehydratase in the wild-type strain showed that deoxy- d -arabino-heptulosonate-7-phosphate synthase was subject to feedback inhibition by l -phe, l -tyrosine, and l -tryptophan. Inhibition by each amino acid was to a similar extent singly or in combination at a 0.5 mM level of each amino acid. Prephenate dehydratase was feedback inhibited by l -phe, but not by l -tyrosine or l -tryptophan or both. In the double analog-resistant mutant BT R -7, deoxy- d -arabino-heptulosonate-7-phosphate synthase had specific activity similar to that in the wild type, and the enzyme was still subject to feedback inhibition. However, prephenate dehydratase had increased specific activity and it was also insensitive to feedback inhibition by l -phe. The overproduction of aromatic amino acids by BT R -7 was thought to be due, at least in part, to deregulation of feedback inhibition of prephenate dehydratase. Chorismate mutase was not subject to feedback inhibition in the wild type and was unaffected in the mutant.