Extracellular Production and Characterization of Two Streptomyces l-Asparaginases

Identification and Thermostability Modification of the Mesophilic L-asparaginase from Limosilactobacillus secaliphilus

L-asparaginase (L-ASNase, E.C.3.5.1.1) could effectively inhibit the formation of acrylamide (AA) by hydrolyzing the AA precursor L-asparagine. However, most of the L-ASNases showed a relatively weak thermostability, posing a big threat on the application of enzyme at high processing temperatures. Here, the recombinant L-ASNase from mesophilic bacteria Limosilactobacillus secaliphilus was identified for the first time. The recombinant enzyme exhibited its optimal activity at pH 8.0 and 60 ℃. Additionally, the thermostability of L. secaliphilus L-ASNase was enhanced by site-directed mutagenesis after multiple sequence alignment. Ten mutants were reasonably constructed, among which the single-point mutants L24Y, S55T, and V155S showed more than 1 ℃ elevated Tm value compared to the wild-type enzyme. In addition, the half-life of mutant at 40, 50, and 55 ℃ was 376.7 min, 62.1 min, and 18.7 min, much higher than that of wild-type enzyme. The molecular dynamic simulation showed that compared to the wild-type enzyme, the structural stability of V155S was greatly strengthened due to the lower RMSF and RMSD value as well as a decreased total energy compared to that of the wild-type enzyme. The results were positive and provided some useful information for the thermostability modification of L-ASNase.

Structural and functional analyses of an L-asparaginase from Geobacillus thermopakistaniensis

Genome sequence of Geobacillus thermopakistaniensis contains an open reading frame annotated as a type II L-asparaginase (ASNaseGt). Critical structural analysis disclosed that ASNaseGt might be a type I L-asparaginase. In order to determine whether it is a type I or type II L-asparaginase, we have performed the structural-functional characterization of the recombinant protein as well as analyzed the localization of ASNaseGt in G. thermopakistaniensis. ASNaseGt exhibited optimal activity at 52 °C and pH 9.5. There was a > 3-fold increase in activity in the presence of β-mercaptoethanol. Apparent Vmax and Km values were 2735 U/mg and 0.35 mM, respectively. ASNaseGt displayed high thermostability with >80 % residual activity even after 6 h of incubation at 55 °C. Recombinant ASNaseGt existed in oligomeric form. Addition of β-mercaptoethanol lowered the degree of oligomerization and displayed that tetrameric form was the most active, with a specific activity of 4300 U/mg. Under physiological conditions, ASNaseGt displayed >50 % of the optimal activity. Localization studies in G. thermopakistaniensis revealed that ASNaseGt is a cytosolic protein. Structural and functional characterization, and localization in G. thermopakistaniensis displayed that ASNaseGt is not a type II but a type I L-asparaginase.

Endophytic Fungi as a Promising Source of Anticancer L-Asparaginase: A Review

L-asparaginase is a tetrameric enzyme from the amidohydrolases family, that catalyzes the breakdown of L-asparagine into L-aspartic acid and ammonia. Since its discovery as an anticancer drug, it is used as one of the prime chemotherapeutic agents to treat acute lymphoblastic leukemia. Apart from its use in the biopharmaceutical industry, it is also used to reduce the formation of a carcinogenic substance called acrylamide in fried, baked, and roasted foods. L-asparaginase is derived from many organisms including plants, bacteria, fungi, and actinomycetes. Currently, L-asparaginase preparations from Escherichia coli and Erwinia chrysanthemi are used in the clinical treatment of acute lymphoblastic leukemia. However, they are associated with low yield and immunogenicity problems. At this juncture, endophytic fungi from medicinal plants have gained much attention as they have several advantages over the available bacterial preparations. Many medicinal plants have been screened for L-asparaginase producing endophytic fungi and several studies have reported potent L-asparaginase producing strains. This review provides insights into fungal endophytes from medicinal plants and their significance as probable alternatives for bacterial L-asparaginase.

[Approaches for improving L-asparaginase expression in heterologous systems]

L-asparaginase (EC 3.5.1.1) is one of the most demanded enzymes used in the pharmaceutical industry as a drug and in the food industry to prevent the formation of toxic acrylamide. Researchers aimed to improve specific activity and reduce side effects to create safer and more potent enzyme products. However, protein modifications and heterologous expression remain problematic in the production of asparaginases from different species. Heterologous expression in optimized producer strains is rationally organized; therefore, modified and heterologous protein expression is enhanced, which is the main strategy in the production of asparaginase. This strategy solves several problems: incorrect protein folding, metabolic load on the producer strain and codon misreading, which affects translation and final protein domains, leading to a decrease in catalytic activity. The main approaches developed to improve the heterologous expression of L-asparaginases are considered in this paper.

Thermo-L-Asparaginases: From the Role in the Viability of Thermophiles and Hyperthermophiles at High Temperatures to a Molecular Understanding of Their Thermoactivity and Thermostability

L-asparaginase (L-ASNase) is a vital enzyme with a broad range of applications in medicine, food industry, and diagnostics. Among various organisms expressing L-ASNases, thermophiles and hyperthermophiles produce enzymes with superior performances-stable and heat resistant thermo-ASNases. This review is an attempt to take a broader view on the thermo-ASNases. Here we discuss the position of thermo-ASNases in the large family of L-ASNases, their role in the heat-tolerance cellular system of thermophiles and hyperthermophiles, and molecular aspects of their thermoactivity and thermostability. Different types of thermo-ASNases exhibit specific L-asparaginase activity and additional secondary activities. All products of these enzymatic reactions are associated with diverse metabolic pathways and are important for mitigating heat stress. Thermo-ASNases are quite distinct from typical mesophilic L-ASNases based on structural properties, kinetic and activity profiles. Here we attempt to summarize the current understanding of the molecular mechanisms of thermo-ASNases' thermoactivity and thermostability, from amino acid composition to structural-functional relationships. Research of these enzymes has fundamental and biotechnological significance. Thermo-ASNases and their improved variants, cloned and expressed in mesophilic hosts, can form a large pool of enzymes with valuable characteristics for biotechnological application.

L-Asparaginase from Penicillium sizovae Produced by a Recombinant Komagataella phaffii Strain

L-asparaginase is an important enzyme in the pharmaceutical field used as treatment for acute lymphoblastic leukemia due to its ability to hydrolyze L-asparagine, an essential amino acid synthesized by normal cells, but not by neoplastic cells. Adverse effects of L-asparaginase formulations are associated with its glutaminase activity and bacterial origin; therefore, it is important to find new sources of L-asparaginase produced by eukaryotic microorganisms with low glutaminase activity. This work aimed to identify the L-asparaginase gene sequence from Penicillium sizovae, a filamentous fungus isolated from the Brazilian Savanna (Cerrado) soil with low glutaminase activity, and to biosynthesize higher yields of this enzyme in the yeast Komagataella phaffii. The L-asparaginase gene sequence of P. sizovae was identified by homology to L-asparaginases from species of Penicillium of the section Citrina: P. citrinum and P. steckii. Partial L-asparaginase from P. sizovae, lacking the periplasmic signaling sequence, was cloned, and expressed intracellularly with highest enzymatic activity achieved by a MUT⁺ clone cultured in BMM expression medium; a value 5-fold greater than that obtained by native L-asparaginase in P. sizovae cells. To the best of our knowledge, this is the first literature report of the heterologous production of an L-asparaginase from a filamentous fungus by a yeast.

A Novel L-Asparaginase from Hyperthermophilic Archaeon Thermococcus sibiricus: Heterologous Expression and Characterization for Biotechnology Application

L-asparaginase (L-ASNase) is a vital enzyme with a broad range of applications in medicine and food industry. Drawbacks of current commercial L-ASNases stimulate the search for better-producing sources of the enzyme, and extremophiles are especially attractive in this view. In this study, a novel L-asparaginase originating from the hyperthermophilic archaeon Thermococcus sibiricus (TsA) was expressed in Escherichia coli, purified and characterized. The enzyme is optimally active at 90 °C and pH 9.0 with a specific activity of 2164 U/mg towards L-asparagine. Kinetic parameters KM and Vmax for the enzyme are 2.8 mM and 1200 µM/min, respectively. TsA is stable in urea solutions 0-6 M and displays no significant changes of the activity in the presence of metal ions Ni2+, Cu2+, Mg2+, Zn2+ and Ca2+ and EDTA added in concentrations 1 and 10 mmol/L except for Fe3+. The enzyme retains 86% of its initial activity after 20 min incubation at 90 °C, which should be enough to reduce acrylamide formation in foods processed at elevated temperatures. TsA displays strong cytotoxic activity toward cancer cell lines K562, A549 and Sk-Br-3, while normal human fibroblasts WI-38 are almost unsensitive to it. The enzyme seems to be a promising candidate for further investigation and biotechnology application.

Efficient control of acrylamide in French fries by an extraordinarily active and thermo-stable l-asparaginase: A lab-scale study

As a potential carcinogen, acrylamide (AA) widely exists in starch-rich foods during frying, triggering international health alerts. l-Asparaginase (l-ASNase, EC 3.5.1.1) could efficiently inhibit the AA by hydrolyzing its precursor l-Asparagine. Here, a novel recombinant l-ASNase from Palaeococcus ferrophilus was identified for the first time. The purified enzyme exhibited its highest activity at pH 8.5 and 95 °C and retained more than 70% relative activity after incubation at 80 °C for 2 h. Compared to untreated French fries, the AA content in the enzyme-treated (10 U/mL, 85 °C, 15 min) French fries was significantly reduced by 79%. Notably, the l-ASNase could remain over 98% of initial activity after three months of storage at 4 °C, suggesting good storage stability. These results demonstrated that P. ferrophilusl-ASNase could be a great candidate in controlling AA in the food industry, especially at high blanching temperature.

Development of Escherichia coli asparaginase II for the Treatment of Acute Lymphocytic Leukemia: In Silico Reduction of asparaginase II Side Effects by a Novel Mutant (V27F)

Acute lymphoblastic leukemia (ALL) is a common blood disease in children that is accountable for many deaths. Due to major improvements in treatment procedures in the past 50 years, the survivability of this disease has risen dramatically to about 90 percent today. L-asparaginase (ASNase) has been used to treat ALL. The glutaminase (GLNase) activity of this enzyme causes some side effects and is unnecessary for anticancer activity. This study investigated mutagenesis in Escherichia coli ASNase II to find a mutant with lower GLNase activity via molecular dynamics (MD) simulation. Residues with low binding energy to asparagine (Asn) and high binding energy to glutamine (Gln) were chosen for mutagenesis. A mutant with low free binding energy to Gln was then selected for molecular docking and MD studies. The results showed that V27F is a good candidate for reducing GLNase activity and that it has little effect on enzyme ASNase activity. A simulation analysis showed that the V27F mutant was more stable than the WT ASNase and that mutagenesis was quite successful.

[L-asparaginases of extremophilic microorganisms in biomedicine]

L-asparaginase is extensively used in the treatment of acute lymphoblastic leukemia and several other lymphoproliferative diseases. In addition to its biomedical application, L-asparaginase is also of prospective use in food industry to reduce the formation of acrylamide, which is classified as probably neurotoxic and carcinogenic to human, and in biosensors for determination of L-asparagine level in medicine and food chemistry. The importance of L-asparaginases in different fields, disadvantages of commercial ferments, and the fact that they are widespread in nature stimuli the search for biobetter L-asparaginases from new producing microorganisms. In this regard, extremofile microorganisms exhibit unique physiological properties such as thermal stability, adaptability to extreme cold conditions, salt and pH tolerance and so provide one of the most valuable sources for novel L-asparaginases. The present review summarizes the recent results on studying the structural, functional, physicochemical and kinetic properties, stability of extremophilic L-asparaginases in comparison with their mesophilic homologues.

A comprehensive review on microbial l-asparaginase: Bioprocessing, characterization, and industrial applications

l-Asparaginase (E.C.3.5.1.1.) is a vital enzyme that hydrolyzes l-asparagine to l-aspartic acid and ammonia. This property of l-asparaginase inhibits the protein synthesis in cancer cells, making l-asparaginase a mainstay of pediatric chemotherapy practices to treat acute lymphoblastic leukemia (ALL) patients. l-Asparaginase is also recognized as one of the important food processing agent. The removal of asparagine by l-asparaginase leads to the reduction of acrylamide formation in fried food items. l-Asparaginase is produced by various organisms including animals, plants, and microorganisms, however, only microorganisms that produce a substantial amount of this enzyme are of commercial significance. The commercial l-asparaginase for healthcare applications is chiefly derived from Escherichia coli and Erwinia chrysanthemi. A high rate of hypersensitivity and adverse reactions limits the long-term clinical use of l-asparaginase. Present review provides thorough information on microbial l-asparaginase bioprocess optimization including submerged fermentation and solid-state fermentation for l-asparaginase production, downstream purification, its characterization, and issues related to the clinical application including toxicity and hypersensitivity. Here, we have highlighted the bioprocess techniques that can produce improved and economically viable yields of l-asparaginase from promising microbial sources in the current scenario where there is an urgent need for alternate l-asparaginase with less adverse effects.

Insights into the Microbial L-Asparaginases: from Production to Practical Applications

L-asparaginase is a valuable protein therapeutic drug utilized for the treatment of leukemia and lymphomas. Administration of asparaginase leads to asparagine starvation causing inhibition of protein synthesis, growth, and proliferation of tumor cells. Besides its clinical significance, the enzyme also finds application in the food sector for mitigation of a cancer-causing agent acrylamide. The numerous applications ensue huge market demands and create a continued interest in the production of costeffective, more specific, less immunogenic and stable formulations which can cater both the clinical and food processing requirements. The current review article approaches the process parameters of submerged and solid-state fermentation strategies for the microbial production of the L-asparaginase from diverse sources, genetic engineering approaches used for the production of L-asparaginase enzyme and major applications in clinical and food sectors. The review also addresses the immunological issues associated with the L-asparaginase usage and the immobilization strategies, drug delivery systems employed to circumvent the toxicity complications are also discussed. The future prospects for microbial Lasparaginase production are discussed at the end of the review article.

Novel mutant of Escherichia coli asparaginase II to reduction of the glutaminase activity in treatment of acute lymphocytic leukemia by molecular dynamics simulations and QM-MM studies

L-Asparaginases (ASNase) belong to a family of amidohydrolases, have both asparaginase and glutaminase activity. Acute lymphocytic leukemia (ALL) is an outrageous disease worldwide. Bacterial ASNase has been used for the treatment of ALL. Glutaminase activity of enzyme causes some side effect and it is not essential for anticancer activity. The aim of this study was engineering of Escherichia coli asparaginase II to find a mutant with reduced glutaminase activity by molecular docking, molecular dynamics (MD) and QM-MM (Quantum mechanics molecular dynamics) simulations. Residues with low free energy of binding to Asn and high free binding energy to Gln were chosen for mutagenesis. Then, a mutant with higher glutaminase free binding energy was selected for further studies. Additionally, the MD simulation and QM-MM computation of wild type (WT) were employed and the selected mutated ASNase were analyzed and discussed. Our data showed that V27T is a good candidate to reduction the glutaminase activity, while has no remarkable effect on asparaginase activity of the enzyme. The simulation analysis revealed that V27T mutant is more stable than WT and mutant simulation was successful completely. QM-MM results confirmed the successfulness of our mutagenesis.

Current applications and different approaches for microbial l-asparaginase production

l-asparaginase (EC 3.5.1.1) is an enzyme that catalysis mainly the asparagine hydrolysis in l-aspartic acid and ammonium. This enzyme is presented in different organisms, such as microorganisms, vegetal, and some animals, including certain rodent's serum, but not unveiled in humans. It can be used as important chemotherapeutic agent for the treatment of a variety of lymphoproliferative disorders and lymphomas (particularly acute lymphoblastic leukemia (ALL) and Hodgkin's lymphoma), and has been a pivotal agent in chemotherapy protocols from around 30 years. Also, other important application is in food industry, by using the properties of this enzyme to reduce acrylamide levels in commercial fried foods, maintaining their characteristics (color, flavor, texture, security, etc.) Actually, l-asparaginase catalyzes the hydrolysis of l-asparagine, not allowing the reaction of reducing sugars with this aminoacid for the generation of acrylamide. Currently, production of l-asparaginase is mainly based in biotechnological production by using some bacteria. However, industrial production also needs research work aiming to obtain better production yields, as well as novel process by applying different microorganisms to increase the range of applications of the produced enzyme. Within this context, this mini-review presents l-asparaginase applications, production by different microorganisms and some limitations, current investigations, as well as some challenges to be achieved for profitable industrial production.

Thermophilic and alkaliphilic Actinobacteria: biology and potential applications

Microbes belonging to the phylum Actinobacteria are prolific sources of antibiotics, clinically useful bioactive compounds and industrially important enzymes. The focus of the current review is on the diversity and potential applications of thermophilic and alkaliphilic actinobacteria, which are highly diverse in their taxonomy and morphology with a variety of adaptations for surviving and thriving in hostile environments. The specific metabolic pathways in these actinobacteria are activated for elaborating pharmaceutically, agriculturally, and biotechnologically relevant biomolecules/bioactive compounds, which find multifarious applications.

Cloning, expression, and characterization of L-asparaginase from a newly isolated Bacillus subtilis B11-06

This study focused on the cloning, overexpression, and characterization of the gene encoding L-asparaginase (ansZ) from a nonpathogenic strain of Bacillus subtilis B11-06. The recombinant enzyme showed high thermostability and low affinity to L-glutamine. The ansZ gene, encoding a putative L-asparaginase II, was amplified by PCR and expressed in B. subtilis 168 using the shuttle vector pMA5. The activity of the recombinant enzyme was 9.98 U/mL, which was significantly higher than that of B. subtilis B11-06. The recombinant enzyme was purified by a two-step procedure including ammonium sulfate fractionation and hydrophobic interaction chromatography. The optimum pH and temperature of the recombinant enzyme were 7.5 and 40 °C, respectively. The enzyme was quite stable at a pH range of 6.0-9.0 and exhibited about 14.7 and 9.0% retention of activity following 2 h incubation at 50 or 60 °C, respectively. The Km for L-asparagine was 0.43 mM, and the Vmax was 77.51 μM/min. Results of this study also revealed the potential industrial application of this enzyme in reducing acrylamide formation during the potato frying process.

Extracellular production and characterization of Streptomyces X-prolyl dipeptidyl aminopeptidase

X-prolyl dipeptidyl aminopeptidases (X-PDAPs) are useful in various food industries. In this study, we performed sequence-based screening to obtain a stable X-PDAP enzyme from thermophilic Streptomyces strains. We found three genes that encoded X-PDAP from Streptomyces thermoluteus subsp. fuscus NBRC 14270 (14270 X-PDAP), Streptomyces thermocyaneoviolaceus NBRC 14271 (14271 X-PDAP), and Streptomyces thermocoerulescens NBRC 14273, which were subsequently cloned and sequenced. The deduced amino acid sequences of these genes showed high similarity, with ~80% identity with each other. The isolated X-PDAPs and an X-PDAP from Streptomyces coelicolor were expressed in Streptomyces lividans using a hyperexpression vector: pTONA5a. Among these genes, only 14270 and 14271 X-PDAPs caused overexpression and extracellular production without artificial signal peptides. We also characterized the biochemical properties of purified 14271 X-PDAP. In addition, we found that, in peptide synthesis via an aminolysis reaction, this enzyme recognized D-amino acid derivatives as acyl acceptors, similar to L-amino acid derivatives.