Microbial l-methioninase: production, molecular characterization, and therapeutic applications

Enzymatic properties of ornithine decarboxylase from Clostridium aceticum DSM1496

Clostridium aceticum DSM1496 is an acid-resistant strain in which ornithine decarboxylase (ODC) plays a crucial role in acid resistance. In this study, we expressed ODC derived from C. aceticum DSM1496 in Escherichia coli BL21 (DE3) and thoroughly examined its enzymatic properties. The enzyme has a molecular weight of 55.27 kDa and uses pyridoxal-5'-phosphate (PLP) as a coenzyme with a Km = 0.31 mM. ODC exhibits optimal activity at pH 7.5, and it maintains high stability even at pH 4.5. The peak reaction temperature for ODC is 30°C. Besides, it can be influenced by certain metal ions such as Mn2+. Although l-ornithine serves as the preferred substrate for ODC, the enzyme also decarboxylates l-arginine and l-lysine simultaneously. The results indicate that ODC derived from C. aceticum DSM1496 exhibits the ability to produce putrescine, cadaverine, and agmatine through decarboxylation. These polyamines have the potential to neutralize acid in an acidic environment, facilitating the growth of microorganisms. These significant findings provide a strong basis for further investigation into the acid-resistant mechanisms contributed by ODC.

Conjugation to gold nanoparticles of methionine gamma-lyase, a cancer-starving enzyme. Physicochemical characterization of the nanocomplex for prospective nanomedicine applications

The pyridoxal 5'-dependent enzyme methionine γ-lyase (MGL) catalyzes the degradation of methionine. This activity has been profitable to develop an antitumor agent exploiting the strict dependence of most malignant cells on the availability of methionine. Indeed, methionine depletion blocks tumor proliferation and leads to an increased susceptibility to anticancer drugs. Here, we explore the conjugation of MGL to gold nanoparticles capped with citrate (AuNPs) as a novel strategy to deliver MGL to cancer cells. Measurements of Transmission Electron Microscopy, Dynamic Light Scattering, Asymmetrical Flow Field-Flow Fractionation, X-ray Photoelectron Spectroscopy, and Circular Dichroism allowed to achieve an extensive biophysical and biochemical characterization of the MGL-AuNP complex including particle size, size distribution, MGL loading yield, enzymatic activity, and impact of gold surface on protein structure. Noticeably, we found that activity retention was improved over time for the enzyme adsorbed to AuNPs with respect to the enzyme free in solution. The acquired body of knowledge on the nanocomplex properties and this encouraging stabilizing effect upon conjugation are the necessary basis for further studies aimed at the evaluation of the therapeutic potential of MGL-AuNP complex in a biological milieu.

Isolation and characterization of Trichoderma harzianum L-methioninase with promising a powerful anticancer

Bioactive components derived from medicinal herbs have recently acquired popularity due to their efficacy in treating various ailments, including cancer and infectious diseases. In this study, the anticancer enzyme, L-methioninase isolated from medicinal plants endophytic fungi, then evaluated its promising therapeutic agents against different types of human cancers. L methionine was purified using column chromatography with the stationary phase of Sephadex G-200 with 6.6-fold purification, which increased the specific activity of 71.3 U/mg of protein with a recovery rate of 48.2 %. On the SDS-PAGE chromatogram, the apparent molecular mass of the isolated enzyme was 48 kDa, and its highest activity was observed at pH 8 and 35 °C. The enzyme was catalytically stable within the pH range of 6.0-9.0 and below 40 °C. This study demonstrates that isolated L-methioninase is particularly efficient against tumour cell lines in vitro. The crude and purified L-methioninase inhibited 60 and 80 % of the growth of the breast cancer cell line (MCF-7), respectively, with an estimated IC50 = 12.6 μg/ml (crude) and IC50 = 5.0 μg/ml for purified L-methioninase from isolate 8 with accession no MZ675362. Because of this, pure L-methioninase has better catalytic characteristics and significant thermal stability, which could be used as a cancer-fighting substance than the enzyme purified from other sources.

Biochemical, molecular and anti-tumor characterization of L-methionine gamma lyase produced by local Pseudomonas sp. in Egypt

A soil inhabiting Pseudomonas sp. has been examined for producing L- methionine gamma-lyase enzyme. The identity of the tested bacteria was verified by VITEK2, and MALDI-TOF analysis in addition to molecular confirmation by 16S rDNA sequence and submitted in Genbank under accession number ON993898.1. Production of the targeted enzyme was done using a commercial medium including L-methionine, as the main substrate. This obtained enzyme was precipitated using acetone (1:1v/v) followed by purification with Sephadex G100 and sepharose columns. The specific activity of the purified enzyme (105.8 µmol/ mg/min) increased by 1.89 folds after the purification steps. The peptide fingerprint of the native MGL was verified from the proteomics analysis, with identical conserved active site domains with database-deposited MGLs. The molecular mass of the pure MGL denatured subunit was (>40 kDa) and that of the native enzyme was (>150 kDa) ensuring their homotetrameric identity. The purified enzyme showed absorption spectra at 280 nm and 420 nm for the apo-MGL and PLP coenzyme, respectively. Amino acids suicide analogues analysis by DTNB, hydroxylamine, iodoacetate, MBTH, mercaptoethanol and guanidine thiocyanate reduced the relative activity of purified MGL. From the kinetic properties, the catalytic effectiveness (K_cat/k_m) of Pseudomonas sp. MGL was 10.8 mM ^-1 S^-1 for methionine and 5.51 mM ^-1 S^-1 for cysteine, respectively. The purified MGL showed highly significant antiproliferative activity towards the liver carcinoma cell line (HEPG-2) and breast carcinoma cell line (MCF-7) with half inhibitory concentration values (IC₅₀) 7.23 U/ml and 21.14 U/ml, respectively. No obvious signs of toxicity on liver and kidney functions in the examined animal models were observed.

Cytotoxic activity of l-lysine alpha-oxidase against leukemia cells

Cancer cells exhibit higher proliferation rates than normal cells, and as a consequence, a higher nutritional demand for metabolites such as amino acids. Such cells demonstrate high expression of amino acid transporters and are significantly dependent on the external uptake of amino acids. Moreover, some types of cancer cells exhibit oncogenic mutations that render them auxotrophic to certain amino acids. This metabolic difference between tumor and normal cells has been explored for developing anticancer drugs. Enzymes capable of depleting certain amino acids in the bloodstream can be employed to inhibit the proliferation of cancer cells and promote cell death. Certain microbial enzymes, such as l-asparaginase and l-amino acid oxidases, have been studied for this purpose. In this paper, we discuss the role of l-asparaginase, the only enzyme currently used as a chemotherapeutic agent. We also review the studies on a new potential antineoplastic agent, l-lysine α-oxidase, an enzyme of l-amino acid oxidase family.

Discovery of Homogentisic Acid as a Precursor in Trimethoprim Metabolism and Natural Product Biosynthesis

Opportunistic infections by Burkholderia cenocepacia are life threatening for patients suffering from cystic fibrosis and chronic granulomatous disease. These infections are often associated with variable clinical outcomes, prompting an interest in molecular investigations of phenotypes associated with disease severity. The production of the pyomelanin pigment is one such phenotype, which was recently linked to the ability of clinical strains to carry out biotransformation of the antibiotic trimethoprim. However, this biotransformation product was not identified, and differences in metabolite production associated with pyomelanin pigmentation are poorly understood. Here, we identify several key metabolites produced exclusively by the pyomelanin-producing strains. To provide insight into the structures and biosynthetic origin of these metabolites, we developed a mass spectrometry-based strategy coupling unsupervised in silico substructure prediction with stable isotope labeling referred to as MAS-SILAC (Metabolite Annotation assisted by Substructure discovery and Stable Isotope Labeling by Amino acids in Cell culture). This approach led to discovery of homogentisic acid as a precursor for biosynthesis of several natural products and for biotransformation of trimethoprim, representing a previously unknown mechanism of antibiotic tolerance. This work presents application of computational methods for analysis of untargeted metabolomic data to link the chemotype of pathogenic microorganisms with a specific phenotype. The observations made in this study provide insights into the clinical significance of the melanated phenotype.

Serine 339 in the Catalysis of γ- and β-Elimination Reactions

Serine 339 of the active site of Citrobacter freundii methionine γ-lyase (MGL) is a conserved amino acid in most pyridoxal 5’-phosphate-dependent enzymes of the cystathionine β-lyase subclass, to which MGL belongs. The reaction mechanism of the MGL-catalyzed γ-elimination reaction is poorly explored. We replaced serine 339 with alanine using site-directed mutagenesis. The replacement of serine 339 with alanine led to a significant (by two orders of magnitude) decrease in efficiency in the catalysis of the γ- and β-elimination reactions by the mutant form of the enzyme. The exchange rates of the C-α- and C-β-protons in the amino acids in complexes consisting of the enzyme and competitive inhibitors decreased by one-two orders of magnitude. The spectral characteristics of the mutant form indicated that the replacement did not lead to significant changes in the conformation and tautomerism of MGL internal aldimine. We crystallized the holoenzyme and determined its spatial structure at 1.7 E resolution. The replacement of serine 339 with alanine did not affect the overall course of the polypeptide chain of the MGL subunit and the tetrameric enzyme structure. An analysis of the obtained kinetic and spectral data, as well as the known spatial structures of C. freundii MGL, indicates that serine 339 is necessary for efficient catalysis of γ- and β-elimination reactions at the stage of C-α-proton abstraction from the external aldimine, the γ-elimination reaction at the stages of coenzyme C4’-atom protonation, and C-β-proton abstraction from a ketimine intermediate.

Purification and Biochemical Characterization of Taxadiene Synthase from Bacillus koreensis and Stenotrophomonas maltophilia

Taxadiene synthase (TDS) is the rate-limiting enzyme of Taxol biosynthesis that cyclizes the geranylgeranyl pyrophosphate into taxadiene. Attenuating Taxol productivity by fungi is the main challenge impeding its industrial application; it is possible that silencing the expression of TDS is the most noticeable genomic feature associated with Taxol-biosynthetic abolishing in fungi. As such, the characterization of TDS with unique biochemical properties and autonomous expression that is independent of transcriptional factors from the host is the main challenge. Thus, the objective of this study was to kinetically characterize TDS from endophytic bacteria isolated from different plants harboring Taxol-producing endophytic fungi. Among the recovered 23 isolates, Bacillus koreensis and Stenotrophomonas maltophilia achieved the highest TDS activity. Upon using the Plackett–Burman design, the TDS productivity achieved by B. koreensis (18.1 µmol/mg/min) and S. maltophilia (14.6 µmol/mg/min) increased by ~2.2-fold over the control. The enzyme was purified by gel-filtration and ion-exchange chromatography with ~15 overall folds and with molecular subunit structure 65 and 80 kDa from B. koreensis and S. maltophilia, respectively. The chemical identity of taxadiene was authenticated from the GC-MS analyses, which provided the same mass fragmentation pattern of authentic taxadiene. The tds gene was screened by PCR with nested primers of the conservative active site domains, and the amplicons were sequenced, displaying a higher similarity with tds from T. baccata and T. brevifolia. The highest TDS activity by both bacterial isolates was recorded at 37–40 °C. The Apo-TDSs retained ~50% of its initial holoenzyme activities, ensuring their metalloproteinic identity. The activity of purified TDS was completely restored upon the addition of Mg2+, confirming the identity of Mg2+ as a cofactor. The TDS activity was dramatically reduced upon the addition of DTNB and MBTH, ensuring the implementation of cysteine-reactive thiols and ammonia groups on their active site domains. This is the first report exploring the autonomous robust expression TDS from B. koreensis and S. maltophilia with a higher affinity to cyclize GGPP into taxadiene, which could be a novel platform for taxadiene production as intermediary metabolites of Taxol biosynthesis.

PeMetR-mediated sulfur assimilation is essential for virulence and patulin biosynthesis in Penicillium expansum

Penicillium expansum, as the causal agent of blue mould and a main producer of mycotoxin patulin, is a global concern for economic and food safety. To date, the nutritional requirements of the pathogen during infection and patulin biosynthesis are poorly understood. Here, we genetically characterized the role of the bZIP transcription factor PeMetR in sulfur metabolism, virulence and patulin biosynthesis of P. expansum. The PeMetR regulator is crucial for normal germination and growth on inorganic S-sources but dispensable for utilization of organic S-sources. Accordingly, it is involved in regulating the expression of genes in sulfur assimilation pathway rather than methionine metabolic processes. Disruption of PeMetR resulted in a complete loss of virulence on various fruits. Additionally, the mutant showed a remarkably reduced ability to produce patulin. Exogenous methionine could partially or completely rescue the impaired phenotypes of the mutant. Inactivation of the sulfur assimilation pathway genes, PesA, PesB, PesC, PesF, generated growth, virulence and patulin production defects similar to those of ΔPeMetR. Overall, our study provides evidence that PeMetR-mediated sulfur assimilation is essential for growth and infection and shows for the first time that regulation of sulfur assimilation affects biosynthesis of an important mycotoxin patulin in P. expansum.

Use of Exogenous Enzymes in Human Therapy: Approved Drugs and Potential Applications

The development of safe and efficacious enzyme-based human therapies has increased greatly in the last decades, thanks to remarkable advances in the understanding of the molecular mechanisms responsible for different diseases, and the characterization of the catalytic activity of relevant exogenous enzymes that may play a remedial effect in the treatment of such pathologies. Several enzyme-based biotherapeutics have been approved by FDA (the U.S. Food and Drug Administration) and EMA (the European Medicines Agency) and many are undergoing clinical trials. Apart from enzyme replacement therapy in human genetic diseases, which is not discussed in this review, approved enzymes for human therapy find applications in several fields, from cancer therapy to thrombolysis and the treatment, e.g., of clotting disorders, cystic fibrosis, lactose intolerance and collagen-based disorders. The majority of therapeutic enzymes are of microbial origin, the most convenient source due to fast, simple and cost-effective production and manipulation. The use of microbial recombinant enzymes has broadened prospects for human therapy but some hurdles such as high immunogenicity, protein instability, short half-life and low substrate affinity, still need to be tackled. Alternative sources of enzymes, with reduced side effects and improved activity, as well as genetic modification of the enzymes and novel delivery systems are constantly searched. Chemical modification strategies, targeted- and/or nanocarrier-mediated delivery, directed evolution and site-specific mutagenesis, fusion proteins generated by genetic manipulation are the most explored tools to reduce toxicity and improve bioavailability and cellular targeting. This review provides a description of exogenous enzymes that are presently employed for the therapeutic management of human diseases with their current FDA/EMA-approved status, along with those already experimented at the clinical level and potential promising candidates.

Purification, characterization and anticancer evaluation of l-methioninase from Trichoderma harzianum

The Trichoderma harzianum l-methioninase was purified 7.15-fold with a recovery of 47.9% and the specific activity of 74.4 U/mg of protein. The purified enzyme has an apparent molecular mass of 48 kDa on SDS-PAGE and exhibited maximum activity at pH 8 and 35 °C. The enzyme was catalytically stable below 50 °C and at a pH range of 6.0-8.5. The thermal inactivation of l-methioninase exhibited first-order kinetics with the k value between 5.71 × 10-4 min-1 and 1.83 × 10-2 min-1. The studies on thermodynamic parameters of l-methioninase indicated the compaction and aggregation of the enzyme molecule during denaturation. This is the first report of thermodynamic analysis of thermal inactivation in l-methioninase. The enzyme activity was enhanced by Li+ and inhibited by Cu2+, Co2+, Fe2+, Hydroxylamine and PMSF. The purified enzyme showed K m , V max and k cat value of 1.19 mM, 21.27 U/mg/min and 16.11 s-1, respectively. The l-methioninase inhibited the growth of human cell lines hepatocellular carcinoma (Hep-G2) and breast carcinoma (MCF-7) with IC50 values of 14.12 μg/ml and 20.07 μg/ml, respectively. The in vivo antitumor activity of l-methioninase was evaluated against DAL cell lines bearing in Swiss albino mice. The enzyme effectively reduced tumor volume, packed cell volume, viable cell count and restored hematological parameters, serum enzyme and lipid profile to normal levels compared to DAL control mice. The present study has demonstrated the high efficacy of Trichoderma harzianum l-methioninase against cancer cell lines in vitro and in vivo conditions. The purified l-methioninase has significant thermal stability and better catalytic properties than the enzyme purified from other sources.

Exploiting the Biosynthetic Potency of Taxol from Fungal Endophytes of Conifers Plants; Genome Mining and Metabolic Manipulation

Endophytic fungi have been considered as a repertoire for bioactive secondary metabolites with potential application in medicine, agriculture and food industry. The biosynthetic pathways by fungal endophytes raise the argument of acquisition of these machineries of such complex metabolites from the plant host. Diterpenoids "Taxol" is the most effective anticancer drug with highest annual sale, since its discovery in 1970 from the Pacific yew tree, Taxus brevifolia. However, the lower yield of Taxol from this natural source (bark of T. brevifolia), availability and vulnerability of this plant to unpredicted fluctuation with the ecological and environmental conditions are the challenges. Endophytic fungi from Taxus spp. opened a new avenue for industrial Taxol production due to their fast growth, cost effectiveness, independence on climatic changes, feasibility of genetic manipulation. However, the anticipation of endophytic fungi for industrial Taxol production has been challenged by the loss of its productivity, due to the metabolic reprograming of cells, downregulating the expression of its encoding genes with subculturing and storage. Thus, the objectives of this review were to (1) Nominate the endophytic fungal isolates with the Taxol producing potency from Taxaceae and Podocarpaceae; (2) Emphasize the different approaches such as molecular manipulation, cultural optimization, co-cultivation for enhancing the Taxol productivities; (3) Accentuate the genome mining of the rate-limiting enzymes for rapid screening the Taxol biosynthetic machinery; (4) Triggering the silenced rate-limiting genes and transcriptional factors to activates the biosynthetic gene cluster of Taxol.

Bacterium Hafnia alvei secretes l-methioninase enzyme: Optimization of the enzyme secretion conditions

I isolated bacteria from blue cheese in order to find bacterial strains secreting l-methioninase enzyme, and optimized the conditions for the most efficient enzyme secretion. The efficient isolate, identified according to the 16S rRNA gene sequence analysis, was Hafnia alvei belonging to Enterobacteriaceae. I confirmed that the H. alvei strain harbored the methionase gene, mdeA (1194 bp). The environmental (pH, temperature) and nutritional (carbon and nitrogen sources and Mg concentration) factors influencing the l-methioninase production of H. alvei were optimized. The highest yield of l-methioninase enzyme was reached after 48 h of incubation when the acidity of the growing medium was adjusted to pH 7.5 and the temperature was 35 °C. The following concentrations of the supplements increased the l-methioninase yield in the medium: galactose (2.0 g L-1), MgSO4 (0.25 g L-1), l-methionine as an inducer (2.0 g L-1), and l-asparagine as an additional N source (1.5 g L-1). I introduce a bacterial strain of H. alvei that is previously unreported to secrete l-methioninase enzyme and show that a carbon source is a mandatory supplement whereas l-methionine is not a mandatory supplement for l-methioninase enzyme production of H. alvei.

Microbial enzymes for deprivation of amino acid metabolism in malignant cells: biological strategy for cancer treatment

Amino acid deprivation therapy (AADT) is emerging as a promising strategy for the development of novel therapeutics against cancer. This biological therapy relies upon the differences in the metabolism of cancer and normal cells. The rapid growth of tumors results in decreased expression of certain enzymes leading to auxotrophy for some specific amino acids. These auxotrophic tumors are targeted by amino acid-depleting enzymes. The depletion of amino acid selectively inhibits tumor growth as the normal cells can synthesize amino acids by their usual machinery. The enzymes used in AADT are mostly obtained from microbes for their easy availability. Microbial L-asparaginase is already approved by FDA for the treatment of acute lymphoblastic leukemia. Arginine deiminase and methionase are under clinical trials and the therapeutic potential of lysine oxidase, glutaminase and phenylalanine ammonia lyase is also being explored. The present review provides an overview of microbial amino acid depriving enzymes. Various attributes of these enzymes like structure, mode of action, production, formulations, and targeted cancers are discussed. The challenges faced and the combat strategies to establish AADT in standard cancer armamentarium are also reviewed.Key Points • Amino acid deprivation therapy is a potential therapy for auxotrophic tumors. • Microbial enzymes are used due to their ease of manipulation and high productivity. • Enzyme properties are improved by PEGylation, encapsulation, and genetic engineering. • AADT can be employed as combinational therapy for better containment of cancer.

Aspergillus nidulans thermostable arginine deiminase-Dextran conjugates with enhanced molecular stability, proteolytic resistance, pharmacokinetic properties and anticancer activity

The potential anticancer activity of arginine deiminase (ADI) via deimination of l-arginine into citrulline has been extensively verified against various arginine-auxotrophic tumors, however, the higher antigenicity, structural instability and in vivo proteolysis are the major challenges that limit this enzyme from further clinical implementation. Since, this clinically applied enzyme was derived from Mycobacterium spp, thus, searching for ADI from eukaryotic microbes "especially thermophilic fungi" could have a novel biochemical, conformational and catalytic properties. Aspergillus nidulans ADI was purified with 5.3 folds, with molecular subunit structure 48 kDa and entire molecular mass 120 kDa, ensuring its homotrimeric identity. The peptide fingerprinting analysis revealing the domain Glu⁹⁵-Gly⁹⁶-Gly⁹⁷ as the conserved active site of A. nidulans ADI, with higher proximity to Mycobacterium ADI clade IV. In an endeavor to fortify the structural stability and anticancer activity of A. nidulans ADI, the enzyme was chemically modified with dextran. The optimal activity of Dextran-ADI conjugates was determined at 0.08:20 M ratio of ADI: Dextran, with an overall increase to ADI molecular subunit mass to ˜100 kDa. ADI was conjugated with dextran via the ε-amino groups interaction of surface lysine residues of ADI. The resistance of Dextran-ADI conjugate to proteolysis had been increased by 2.5 folds to proteinase K and trypsin, suggesting the shielding of >50% of ADI surface proteolytic recognition sites. The native and Dextran-ADI conjugates have the same optimum reaction temperature (37 °C), reaction pH and pH stability (7.0-8.0) with dependency on K⁺ ions as a cofactor. Dextran-ADI conjugates exhibited a higher thermal stability by ˜ 2 folds for all the tested temperatures, ensuring the acquired structural and catalytic stability upon dextran conjugation. Dextran conjugation slightly protect the reactive amino and thiols groups of surface amino acids of ADI from amino acids suicide inhibitors. The affinity of ADI was increased by 5.3 folds to free L-arginine with a dramatic reduction in citrullination of peptidylarginine residues upon dextran conjugation. The anticancer activity of ADI to breast (MCF-7), liver (HepG-2) and colon (HCT8, HT29, DLD1 and LS174 T) cancer cell lines was increased by 1.7 folds with dextran conjugation in vitro. Pharmacokinetically, the half-life time of ADI was increased by 1.7 folds upon dextran conjugation, in vivo. From the biochemical and hematological parameters, ADIs had no signs of toxicity to the experimental animals. In addition to the dramatic reduction of L-arginine in serum, citrulline level was increased by 2.5 folds upon dextran conjugation of ADI. This is first report exploring thermostable ADI from thermophilic A. nidulans with robust structural stability, catalytic efficiency and proteolytic resistance.

Purification and Characterization of Ornithine Decarboxylase from Aspergillus terreus; Kinetics of Inhibition by Various Inhibitors

l-Ornithine decarboxylase (ODC) is the rate-limiting enzyme of de novo polyamine synthesis in humans and fungi. Elevated levels of polyamine by over-induction of ODC activity in response to tumor-promoting factors has been frequently reported. Since ODC from fungi and human have the same molecular properties and regulatory mechanisms, thus, fungal ODC has been used as model enzyme in the preliminary studies. Thus, the aim of this work was to purify ODC from fungi, and assess its kinetics of inhibition towards various compounds. Forty fungal isolates were screened for ODC production, twenty fungal isolates have the higher potency to grow on L-ornithine as sole nitrogen source. Aspergillus terreus was the most potent ODC producer (2.1 µmol/mg/min), followed by Penicillium crustosum and Fusarium fujikuori. These isolates were molecularly identified based on their ITS sequences, which have been deposited in the NCBI database under accession numbers MH156195, MH155304 and MH152411, respectively. ODC was purified and characterized from A. terreus using SDS-PAGE, showing a whole molecule mass of ~110 kDa and a 50 kDa subunit structure revealing its homodimeric identity. The enzyme had a maximum activity at 37 °C, pH 7.4-7.8 and thermal stability for 20 h at 37 °C, and 90 days storage stability at 4 °C. A. terreus ODC had a maximum affinity (K_m) for l-ornithine, l-lysine and l-arginine (0.95, 1.34 and 1.4 mM) and catalytic efficiency (k_cat/K_m) (4.6, 2.83, 2.46 × 10^-5 mM^-1·s^-1). The enzyme activity was strongly inhibited by DFMO (0.02 µg/mL), curcumin (IC₅₀ 0.04 µg/mL), propargylglycine (20.9 µg/mL) and hydroxylamine (32.9 µg/mL). These results emphasize the strong inhibitory effect of curcumin on ODC activity and subsequent polyamine synthesis. Further molecular dynamic studies to elucidate the mechanistics of ODC inhibition by curcumin are ongoing.

Methionine Gamma Lyase from Clostridium sporogenes Increases the Anticancer Efficacy of Doxorubicin on A549 Cancer Cells In Vitro and Human Cancer Xenografts

The anticancer efficacy of methionine γ-lyase (MGL) from Clostridium sporogenes (C. sporogenes) is described. MGL was active against cancer cells in vitro and in vivo. Doxorubicin (DOX) and MGL were more effective on A549 human lung-cancer growth inhibition than either agent alone in vitro and in vivo.

Amino Acid Degrading Enzymes and their Application in Cancer Therapy

BACKGROUND

Amino acids are essential components in various biochemical pathways. The deprivation of certain amino acids is an antimetabolite strategy for the treatment of amino acid-dependent cancers which exploits the compromised metabolism of malignant cells. Several studies have focused on the development and preclinical and clinical evaluation of amino acid degrading enzymes, namely L-asparaginase, L-methionine γ-lyase, L-arginine deiminase, L-lysine α-oxidase. Further research into cancer cell metabolism may therefore define possible targets for controlling tumor growth.

OBJECTIVE

The purpose of this review was to summarize recent progress in the relationship between amino acids metabolism and cancer therapy, with a particular focus on Lasparagine, L-methionine, L-arginine and L-lysine degrading enzymes and their formulations, which have been successfully used in the treatment of several types of cancer.

METHODS

We carried out a structured search among literature regarding to amino acid degrading enzymes. The main aspects of search were in vitro and in vivo studies, clinical trials concerning application of these enzymes in oncology.

RESULTS

Most published research are on the subject of L-asparaginase properties and it's use for cancer treatment. L-arginine deiminase has shown promising results in a phase II trial in advanced melanoma and hepatocellular carcinoma. Other enzymes, in particular Lmethionine γ-lyase and L-lysine α-oxidase, were effective in vitro and in vivo.

CONCLUSION

The findings of this review revealed that therapy based on amino acid depletion may have the potential application for cancer treatment but further clinical investigations are required to provide the efficacy and safety of these agents.

Isolation and screening of extracellular anticancer enzymes from halophilic and halotolerant bacteria from different saline environments in Iran

It was confirmed that several enzymes have anti-cancer activity. The enzymes L-asparaginase, L-glutaminase, and L-arginase were chosen according to amino acids starvation in cancer cells and screened in halophilic and halotolerant bacteria, given probably less immunological reactions of halophilic or halotolerant enzymes in patients. Out of 110 halophilic and halotolerant strains, isolated from different saline environments in Iran and screened, some could produce a variety of anticancer enzymes. A total of 29, 4, and 2 strains produced L-asparaginase, L-glutaminase, and L-arginase, respectively. According to the phenotypic characteristics and partial 16S rRNA gene sequence analysis, the positive strains-strains with the ability to produce these anticancer enzymes-were identified as the members of the genera: Bacillus, Dietzia, Halobacillus, Rhodococcus, Paenibacillus and Planococcus as Gram-positive bacteria and Pseudomonas, Marinobacter, Halomonas, Idiomarina, Vibrio and Stappia as Gram-negative bacteria. The production of anticancer enzymes was mostly observed in the rod-shaped Gram-negative isolates, particularly in the members of the genera Halomonas and Marinobacter. Most of the enzymes were produced in the stationary phase of growth and the maximum enzyme activity was experienced in strain GBPx3 (Vibrio sp.) for L-asparaginase at 1.0 IU/ml, strain R₂S₂₅ (Rhodococcus sp.) for L-glutaminase at 0.6 IU/ml and strain GAAy3 (Planococcus sp.) for L-arginase at 3.1 IU/ml. The optimum temperature and pH for L-asparaginase and L-glutaminase activities in selected strains were similar to the physiological conditions of human body and the enzymes could tolerate NaCl up to 7.5% concentration.

Biochemical characterization of peptidylarginine deiminase-like orthologs from thermotolerant Emericella dentata and Aspergillus nidulans

Peptidylarginine deiminases (PADs) are a group of hydrolases, mediating the deimination of peptidylarginine residues into peptidyl-citrulline. Equivocal protein citrullination by PADs of fungal pathogens has a strong relation to the progression of multiple human diseases, however, the biochemical properties of fungal PADs remain ambiguous. Thus, this is the first report exploring the molecular properties of PAD from thermotolerant fungi, to imitate the human temperature. The teleomorph Emericella dentata and anamorph Aspergillus nidulans have been morphologically and molecularly identified, with observed robust growth at 37-40 °C, and strong PAD productivity. The physiological profiles of E. dentata and A. nidulans for PADs production in response to carbon, nitrogen sources, initial medium pH and incubation temperature were relatively identical, emphasizing the taxonomical proximity of these fungal isolates. PADs were purified from E. dentata and A. nidulans with apparent molecular masses 41 and 48 kDa, respectively. The peptide fingerprints of PADs from E. dentata and A. nidulans have been analyzed by MALDI-TOF/MS, displaying a higher sequence similarity to human PAD4 by 18% and 31%, respectively. The conserved peptide sequences of E. dentata and A. nidulans PADs displayed a higher similarity to human PAD than A. fumigatus PADs clade. PADs from both fungal isolates have an optimum pH and pH stability at 7.0-8.0, with putative pI 5.0-5.5, higher structural denaturation at pH 4.0-5.5 and 9.5-12 as revealed from absorbance at λ₂₈₀nm. E. dentata PAD had a higher conformationally thermal stability than A. nidulans PAD as revealed from its lower K_r value. From the proteolytic mapping, the orientation of trypsinolytic recognition sites on the PADs surface from both fungal isolates was very similar. PADs from both isolates are calcium dependent, with participation of serine and cysteine residues on their catalytic sites. PADs displayed a higher affinity to deiminate the peptidylarginine residues with a feeble affinity to work as ADI. So, PADs from E. dentata and A. nidulans had a relatively similar conformational and kinetic properties. Further molecular modeling analysis are ongoing to explore the role of PADs in citrullination of human proteins in Aspergillosis, that will open a new avenue for unraveling the vague of protein-protein interaction of human A. nidulans pathogen.

Revisiting the methionine salvage pathway and its paralogues

Methionine is essential for life. Its chemistry makes it fragile in the presence of oxygen. Aerobic living organisms have selected a salvage pathway (the MSP) that uses dioxygen to regenerate methionine, associated to a ratchet-like step that prevents methionine back degradation. Here, we describe the variation on this theme, developed across the tree of life. Oxygen appeared long after life had developed on Earth. The canonical MSP evolved from ancestors that used both predecessors of ribulose bisphosphate carboxylase oxygenase (RuBisCO) and methanethiol in intermediate steps. We document how these likely promiscuous pathways were also used to metabolize the omnipresent by-products of S-adenosylmethionine radical enzymes as well as the aromatic and isoprene skeleton of quinone electron acceptors.

Enzymes in Metabolic Anticancer Therapy

Cancer treatment has greatly improved over the last 50 years, but it remains challenging in several cases. Useful therapeutic targets are normally unique peculiarities of cancer cells that distinguish them from normal cells and that can be tackled with appropriate drugs. It is now known that cell metabolism is rewired during tumorigenesis and metastasis as a consequence of oncogene activation and oncosuppressors inactivation, leading to a new cellular homeostasis typically directed towards anabolism. Because of these modifications, cells can become strongly or absolutely dependent on specific substrates, like sugars, lipids or amino acids. Cancer addictions are a relevant target for therapy, as removal of an essential substrate can lead to their selective cell-cycle arrest or even to cell death, leaving normal cells untouched. Enzymes can act as powerful agents in this respect, as demonstrated by asparaginase, which has been included in the treatment of Acute Lymphoblastic Leukemia for half a century. In this review, a short outline of cancer addictions will be provided, focusing on the main cancer amino acid dependencies described so far. Therapeutic enzymes which have been already experimented at the clinical level will be discussed, along with novel potential candidates that we propose as new promising molecules. The intrinsic limitations of their present molecular forms, along with molecular engineering solutions to explore, will also be presented.

Methionine gamma lyase from Clostridium sporogenes increases the anticancer effect of doxorubicin in A549 cells and human cancer xenografts

The anti-cancer efficacy of methionine γ-lyase (MGL) from Clostridium sporogenes (C. sporogenes) is described. MGL was active against cancer models in vitro and in vivo. The calculated EC50 values for MGL were 4.4 U/ml for A549, 7.5 U/ml for SK-BR3, 2.4 U/ml for SKOV3, and 0.4 U/ml for MCF7 cells. The combination of doxorubicin (DOX) and MGL was more effective for A549 human lung cancer growth inhibition than either agent alone in vitro and in vivo. MGL reduced the EC50 of doxorubicin from 35.9 μg/mL to 0.01-0.265 μg/mL. The growth inhibitory effect of DOX + MGL on A549 xenografts in vivo was reflective of the results obtained in vitro. The inhibition rate of tumor growth in the combined arm was 57%, significantly higher than that in the doxorubicin (p = 0.033)-alone arm.

Methionine tumor starvation by erythrocyte-encapsulated methionine gamma-lyase activity controlled with per os vitamin B6

Erymet is a new therapy resulting from the encapsulation of a methionine gamma-lyase (MGL; EC number 4.4.1.11) in red blood cells (RBC). The aim of this study was to evaluate erymet potential efficacy in methionine (Met)-dependent cancers. We produced a highly purified MGL using a cGMP process, determined the pharmacokinetics/pharmacodynamics (PK/PD) properties of erymet in mice, and assessed its efficacy on tumor growth prevention. Cytotoxicity of purified MGL was tested in six cancer cell lines. CD1 mice were injected with single erymet product supplemented or not with vitamin B6 vitamer pyridoxine (PN; a precursor of PLP cofactor). NMRI nude mice were xenografted in the flank with U-87 MG-luc2 glioblastoma cells for tumor growth study following five intravenous (IV) injections of erymet with daily PN oral administration. Endpoints included efficacy and event-free survival (EFS). Finally, a repeated dose toxicity study of erymet combined with PN cofactor was conducted in CD1 mice. Recombinant MGL was cytotoxic on 4/6 cell lines tested. MGL half-life was increased from <24 h to 9-12 days when encapsulated in RBC. Conversion of PN into PLP by RBC was demonstrated. Combined erymet + PN treatment led to a sustained Met depletion in plasma for several days with a 85% reduction of tumor volume after 45 days following cells implantation, and a significant EFS prolongation for treated mice. Repeated injections in mice exhibited a very good tolerability with only minor impact on clinical state (piloerection, lean aspect) and a slight decrease in hemoglobin and triglyceride concentrations. This study demonstrated that encapsulation of methioninase inside erythrocyte greatly enhanced pharmacokinetics properties of the enzyme and is efficacy against tumor growth. The perspective on these results is the clinical evaluation of the erymet product in patients with Met starvation-sensitive tumors.

Molecular and Spectroscopic Characterization of Aspergillus flavipes and Pseudomonas putida L-Methionine γ-Lyase in Vitro

Pseudomonas putida L-methionine γ-lyase (PpMGL) has been recognized as an efficient anticancer agent, however, its antigenicity and stability remain as critical challenges for its clinical use. From our studies, Aspergillus flavipes L-methionine γ-lyase (AfMGL) displayed more affordable biochemical properties than PpMGL. Thus, the objective of this work was to comparatively assess the functional properties of AfMGL and PpMGL via stability of their internal aldimine linkage, tautomerism of pyridoxal 5'-phosphate (PLP) and structural stability responsive to physicochemical factors. The internal Schiff base of AfMGL and PpMGL have the same stability to hydroxylamine and human serum albumin. Acidic pHs resulted in strong cleavage of the internal Schiff base, inducing the unfolding of MGLs, compared to neutral-alkaline pHs. At λ 280 nm excitation, both AfMGL and PpMGL have identical fluorescence emission spectra at λ 335 nm for the intrinsic tryptophan and λ 560 nm for the internal Schiff base. The maximum PLP tautomeric shift of ketoenamine to enolimine was detected at acidic pH causing complete enzyme unfolding, subunits dissociation and tautomeric shift of intrinsic PLP, rather than neutral-alkaline ones. The T _m of AfMGL and PpMGL in presence of thermal stabilizer/ destabilizer was assayed by DSF. The T _m of AfMGL and PpMGL was 73.1 °C and 74.4 °C, respectively, suggesting the higher proximity to the tertiary structure of both enzymes. The T _m of AfMGL and PpMGL was slightly increased by trehalose and EDTA in contrast to guanidine HCl and urea. The active site and PLP-binding domains are identically conserved in both AfMGL and PpMGL.

Clonostachys rosea demethiolase STR3 controls the conversion of methionine into methanethiol

Eukaryote-derived methioninase, catalyzing the one-step degradation of methionine (Met) to methanethiol (MTL), has received much attention for its low immunogenic potential and use as a therapeutic agent against Met-dependent tumors. Although biological and chemical degradation pathways for Met-MTL conversion are proposed, the concrete molecular mechanism for Met-MTL conversion in eukaryotes is still unclear. Previous studies demonstrated that α-keto-methylthiobutyric acid (KMBA), the intermediate for Met-MTL conversion, was located extracellularly and the demethiolase STR3 possessed no activities towards Met, which rule out the possibility of intracellular Met-MTL conversion pathway inside eukaryotes. We report here that degradation of Met resulted in intracellular accumulation of KMBA in Clonostachys rosea. Addition of Met to culture media led to the production of MTL and downregulation of STR3, while incubation of Met with surrogate substrate α-ketoglutaric acid enhanced the synthesis of MTL and triggered the upregulation of STR3. Subsequent biochemical analysis with recombinant STR3 showed that STR3 directly converted both Met and its transamination product KMBA to MTL. These results indicated that STR3 as rate-limiting enzyme degrades Met and KMBA into MTL. Our findings suggest STR3 is a potential target for therapeutic agents against Met-dependent tumors and aging.

Recombinant Engineering of L-Methioninase Using Two Different Promoter and Expression Systems and in vitro Analysis of Its Anticancer Efficacy on Different Human Cancer Cell Lines

Recombinant methioninase (rMETase) is an enzyme that has antitumor activity. In this work, METase gene from Pseudomonas putida ATTCC 8209 was cloned to pT7-7 plasmid (yielded, PT7-METase-R7 clone) and expressed in E. coli strain BL21 (DE3). A protein band with a molecular massof 42 kDa was visualized by SDS-PAGE. The applied protocol yielded a total protein of 3.13 g with a recovery of 66.89% and a specific activity of 18.59 U mg-1 which considered as a low yield. However, when the METase gene was cloned to the vector (pTrc99A, clone: pTrc99A-MET-3) cells of E. coli JM109 yielded a total protein of 32.63 g with a recovery of 41.62% and a specific activity of 54.86 U mg-1 which revealed that the enhancement of METase gene expression by trc promoter was more than the T7 RNA polymerase promoter. The t1/2 of the rMETase was 2 h asanalyzed in mice by IV injection. Antitumor efficacy of rMETase was studied in five human cancer cell lines. At 1 U mL-1 the growth rate of treated colon cancer cell lines, Colo205 and SW620, with rMETase was 46 and 32% relative to control, respectively. With the ovarian cancer cell line (A2780) rMETase produced an inhibition effect of 54% at 1.5 U mL-1. In addition, the growth rate was reduced to 45 and 53% with the skin cancer cell line (A375) and the breast cancer cell line (MCF-7), respectively. These results indicate the feasibility of rMETase for use as a potent antitumor agent.

Transcriptional and Proteomic Profiling of Aspergillus flavipes in Response to Sulfur Starvation

Aspergillus flavipes has received considerable interest due to its potential to produce therapeutic enzymes involved in sulfur amino acid metabolism. In natural habitats, A. flavipes survives under sulfur limitations by mobilizing endogenous and exogenous sulfur to operate diverse cellular processes. Sulfur limitation affects virulence and pathogenicity, and modulates proteome of sulfur assimilating enzymes of several fungi. However, there are no previous reports aimed at exploring effects of sulfur limitation on the regulation of A. flavipes sulfur metabolism enzymes at the transcriptional, post-transcriptional and proteomic levels. In this report, we show that sulfur limitation affects morphological and physiological responses of A. flavipes. Transcription and enzymatic activities of several key sulfur metabolism genes, ATP-sulfurylase, sulfite reductase, methionine permease, cysteine synthase, cystathionine β- and γ-lyase, glutathione reductase and glutathione peroxidase were increased under sulfur starvation conditions. A 50 kDa protein band was strongly induced by sulfur starvation, and the proteomic analyses of this protein band using LC-MS/MS revealed similarity to many proteins involved in the sulfur metabolism pathway.

Purification, Characterization of L-Methioninase from Candida tropicalis, and Its Application as an Anticancer

The aim of the present study is to purify L-methioninase from Candida tropicalis 34.19-fold with 27.98% recovery after ion exchange chromatography followed by gel filtration. The purified enzyme revealed a single band on SDS-PAGE gel with a molecular weight of 46 KDa. Its optimum temperature was 45 to 55 and thermal stability was 55°C for 15 min. The enzyme had optimum pH at 6.5 and stability at a pH range of 5.5 to 7.0 for 24 hr. The maximum activity was observed with substrate concentration of 30 µM and Km was 0.5 mM. The enzyme was strongly inhibited by Cd(+2) and Cu(+2) while it was enhanced by Na(+), Ni(+2), and Mg(+2) at 10 mM while Ca(+2) had slight activation at 20 mM. In addition, the potential application of the L-methioninase as an anticancer agent against various types of tumor cell lines is discussed.

Biochemical and Pharmacokinetic Properties of PEGylated Cystathionine γ-Lyase from KF723837

Cystathionine &#947;-lyase (CGL) was purified to its electrophoretic homogeneity from<i> Aspergillus carneus</i> by various chromatographic approaches. The purified enzyme has four identical subunits of 52 kDa based on SDS and native PAGE analyses. To improve its structural stability, purified CGL was modified by covalent binding to polyethylene glycol moieties. The specific activity of free-CGL and PEG-CGL was 59.71 and 48.71 U/mg, respectively, with a PEGylation yield of 81.5 and 70.7% modification of surface ε-amino groups. Free- and modified CGL have the same pattern of pH stability (8.0-9.0). At 50°C, the thermal stability [half-life time (T_1/2)] of PEG-CGL was increased by 40% in comparison to free-CGL. The activity of CGL was completely inhibited by hydroxylamine and Hg⁺², with no effect by EDTA. Free-CGL (0.04 m<smlcap>M</smlcap>^-1s^-1) and PEG-CGL (0.03 m<smlcap>M</smlcap>^-1s^-1) have a similar catalytic efficiency to <smlcap>L</smlcap>-cystathionine as a substrate. The inhibition constant values of propargylglycine were 0.31 and 0.52 µ<smlcap>M</smlcap> for the free- and PEG-CGL, respectively. By in vitro proteolysis, PEG-CGL retains >50% of its initial activity compared to <10% of the free-CGL for acid protease for 30 min. From in vivo pharmacokinetics in New Zealand white rabbits, the T_1/2 was 19.1 and 28.9 h for the Holo free-CGL and PEG-CGL, respectively, ensuring the role of PEGylation on shielding the CGL surface from proteolytic attack, reducing its antigenicity, and stabilizing its internal Schiff base. By external infusion of pyridoxal 5′-phosphate (10 µ<smlcap>M</smlcap>), the T_1/2 of free- and PEG-CGL was prolonged to 24 and 33 h, respectively, so dissociation of pyridoxal 5′-phosphate was one of the main causes of loss of enzyme activity. The biochemical and hematological responses of rabbits to free- and PEG-CGL were assessed, with relative similarity to the negative control, confirming the nil toxicity of enzymes. The titer of IgG was duplicated in response to free- versus PEG-CGL after 45 days. To the best of our knowledge, this is the first report concerned with purification and PEGylation of CGL from fungi, with higher affinity for <smlcap>L</smlcap>-cystathionine. With further molecular studies, CGL will be a promising enzyme against various cardiovascular diseases and antioxidant deficiency, as well as for generation of a neurotransmitter (H₂S).

Screening, morphological and molecular characterization of fungi producing cystathionine γ-lyase

The potency for production of cystathionine γ-lyase (CGL) by the fungal isolates was screened. Among the tested twenty-two isolates, Aspergillus carneus was the potent CGL producer (6.29 U/mg), followed by A. ochraceous (6.03 U/mg), A. versicolor (2.51 U/mg), A. candidus (2.12 U/mg), A. niveus and Penicillium notatum (2.0 U/mg). The potent six isolates producing CGL was characterized morphologically, A. carneus KF723837 was further molecularly characterized based on the sequence of 18S-28S rDNA. Upon sulfur starvation, the yield of A. carneus extracellular CGL was increased by about 1.7- and 4.1-fold comparing to non-sulfur starved and L-methionine free medium, respectively. Also, the uptake of L-methionine was duplicated upon sulfur starvation, assuming the activation of specific transporters for L-methionine and efflux of CGL. Also, the intracellular thiols and GDH activity of A. carneus was strongly increased by S starvation, revealing the activation of in vivo metabolic antioxidant systems. Upon irradiation of A. carneus by 2.0 kGy of γ-rays, the activity of CGL was increased by two-fold, regarding to control, with an obvious decreases on its yield upon further doses. Practically, CGL activity from the solid A. carneus cultures, using rice bran as substrate, was increased by 1.2-fold, comparing to submerged cultures, under optimum conditions.

Purification, immobilization, and biochemical characterization of l-arginine deiminase from thermophilic Aspergillus fumigatus KJ434941: anticancer activity in vitro

l-Arginine deiminase (ADI) has a powerful anticancer activity against various tumors, via arginine depletion, arresting the cell cycle at G1 phase. However, the current clinically tried bacterial ADI displayed a higher antigenicity and lower thermal stability. Thus, our objective was to purify and characterize this enzyme from thermophilic fungi, to explore its catalytic and antigenic properties for therapeutic uses. ADI was purified from thermophilic Aspergillus fumigatus KJ434941 to its electrophoretic homogeneity by 5.1-fold, with molecular subunit 50 kDa. The purified ADI was PEGylated and covalently immobilized on dextran to explore its catalytic properties. The specific activity of free ADI, PEG-ADI, and Dex-ADI was 26.7, 21.5, and 18.0 U/mg, respectively. At 50°C, PEG-ADI displays twofold resistance to thermal denaturation (t1/2 13.9 h), than free ADI (t1/2 6.9 h), while at 70°C, the thermal stability of PEG-ADI was increased by 1.7-fold, with similar stability to Dex-ADI with the free one. Kinetically, free ADI had the higher catalytic affinity to arginine, followed by PEG-ADI and Dex-ADI. Upon proteolysis for 30 min, the residual activity of native ADI, PEG-ADI, and Dex-AD was 8.0, 32.0, and 20.0% for proteinase K and 10.0, 52.0, and 90.0% for acid protease, respectively. The anticancer activity of the ADIs was assessed against HCT, HEP-G2, and MCF7, in vitro. The free and PEG-ADI exhibits a similar cytotoxic efficacy for the tested cells, lower than Dex-ADI. The free ADI had IC50 value 22.0, 16.6, and 13.9 U/mL, while Dex-ADI had 3.98, 5.18, and 4.43 U/mL for HCT, MCF7, and HEPG-2, respectively. The in vitro anticancer activity of ADI against HCT, MCF7, and HEPG-2 was increased by five-, three-, and threefold upon covalent modification by dextran. The biochemical and hematological parameters of the experimented animals were not affected by ADIs dosing, with no signs of anti-ADI immunoglobulins in vivo. The in vivo half-life time of free ADI, PEG-ADI, and Dex-ADI was 29.7, 91.1, 59.6 h, respectively. The present findings explored a novel thermostable, less antigenic ADI from thermophilic A. fumigatus, with further molecular and crystallographic analyses, this enzyme will be a powerful candidate for clinical trials.

Selenium and Human Health: Witnessing a Copernican Revolution?

In humans, selenium was hypothesized to lower the risk of several chronic diseases, mainly due to the antioxidant activity of selenium-containing proteins. Recent epidemiologic and laboratory studies, however, are changing our perception of the biological effects of this nutritionally essential trace element. We reviewed the most recent epidemiologic and biochemical literature on selenium, synthesizing the findings from these studies into a unifying view. Randomized trials have shown that selenium did not protect against cancer and other chronic diseases, but even increased the risk of specific neoplasms such as advanced prostate cancer and skin cancer, in addition to type 2 diabetes. Biochemical studies indicate that selenium may exert a broad pattern of toxic effects at unexpectedly low concentrations. Furthermore, its upregulation of antioxidant proteins (selenium-dependent and selenium-independent) may be a manifestation of self-induced oxidative stress. In conclusion, toxic effects of selenium species occur at lower concentrations than previously believed. Those effects may include a large range of proteomic changes and adverse health effects in humans. Since the effects of environmental exposure to this element on human health still remain partially unknown, but are potentially serious, the toxicity of selenium exposure should be further investigated and considered as a public health priority.

Pre-steady-state kinetic and structural analysis of interaction of methionine γ-lyase from Citrobacter freundii with inhibitors

Methionine γ-lyase (MGL) catalyzes the γ-elimination of l-methionine and its derivatives as well as the β-elimination of l-cysteine and its analogs. These reactions yield α-keto acids and thiols. The mechanism of chemical conversion of amino acids includes numerous reaction intermediates. The detailed analysis of MGL interaction with glycine, l-alanine, l-norvaline, and l-cycloserine was performed by pre-steady-state stopped-flow kinetics. The structure of side chains of the amino acids is important both for their binding with enzyme and for the stability of the external aldimine and ketimine intermediates. X-ray structure of the MGL·l-cycloserine complex has been solved at 1.6 Å resolution. The structure models the ketimine intermediate of physiological reaction. The results elucidate the mechanisms of the intermediate interconversion at the stages of external aldimine and ketimine formation.

Purification and immobilization of L-arginase from thermotolerant Penicillium chrysogenum KJ185377.1; with unique kinetic properties as thermostable anticancer enzyme

L-Arginase, hydrolyzing L-arginine to L-ornithine and urea, is a powerful anticancer, L-arginine-depleting agent, against argininosuccinate synthase expressing tumors. Otherwise, the higher antigenicity and lower thermal stability of this enzyme was the main biochemical hurdles. Since, the intrinsic thermal stability of enzymes follow the physiological temperature of their producer, thus, characterization of L-arginase from thermotolerant Penicillium chrysogenum was the objective of this study. L-Arginase (Arg) was purified to its homogeneity from P. chrysogenum by 10.1-fold, with 37.0 kDa under denaturing PAGE, optimum reaction at 50 °C, pH stability (6.8-7.9), with highest molar ratio of constitutional arginine, glutamic acid, lysine and aspartic acid. The purified enzyme was PEGylated and immobilized on chitosan, with 41.9 and 22.1 % yield of immobilization. At 40 °C, the T1/2 value of free-Arg, PEG-Arg and Chit-Arg was 10.4, 15.6, 20.5 h, respectively. The free-Arg and Chit-Arg have a higher affinity to L-arginine (K m 4.8 mM), while, PEG-Arg affinity was decreased by about 3 fold (K m 15.2 mM). The inhibitory constants to the free and PEG-Arg were relatively similar towards HA and PPG. The IC50 for the free enzyme against HEPG-2 and A549 tumor cells was 0.136 and 0.165 U/ml, comparing to 0.232 and 0.496 U/ml for PEG-Arg, respectively. The in vivo T1/2 to the free Arg and PEG-Arg was 16.4 and 20.4 h, respectively as holo-enzyme. The residual L-arginine level upon using free Arg was 156.9 and 144.5 µM, after 6 and 8 h, respectively, regarding to initials at 253.6 µM, while for Peg-Arg the level of L-arginine was nil till 7 h of initial dosing. The titer of IgG was induced by 10-15 % in response to free-Arg after 28 days comparing to IgG titer for PEG-Arg.

L-methionase: a therapeutic enzyme to treat malignancies

Cancer is an increasing cause of mortality and morbidity throughout the world. L-methionase has potential application against many types of cancers. L-Methionase is an intracellular enzyme in bacterial species, an extracellular enzyme in fungi, and absent in mammals. L-Methionase producing bacterial strain(s) can be isolated by 5,5′-dithio-bis-(2-nitrobenzoic acid) as a screening dye. L-Methionine plays an important role in tumour cells. These cells become methionine dependent and eventually follow apoptosis due to methionine limitation in cancer cells. L-Methionine also plays an indispensable role in gene activation and inactivation due to hypermethylation and/or hypomethylation. Membrane transporters such as GLUT1 and ion channels like Na²⁺, Ca²⁺, K⁺, and Cl⁻ become overexpressed. Further, the α-subunit of ATP synthase plays a role in cancer cells growth and development by providing them enhanced nutritional requirements. Currently, selenomethionine is also used as a prodrug in cancer therapy along with enzyme methionase that converts prodrug into active toxic chemical(s) that causes death of cancerous cells/tissue. More recently, fusion protein (FP) consisting of L-methionase linked to annexin-V has been used in cancer therapy. The fusion proteins have advantage that they have specificity only for cancer cells and do not harm the normal cells.