Cloning and characterization of Halomonas elongata L-asparaginase, a promising chemotherapeutic agent

Production of highly cytotoxic and low immunogenic L-asparaginase from Stenotrophomonas maltophilia EMCC2297

L-asparaginase is an important therapeutic enzyme that is frequently utilized in the chemotherapy regimens of adults as well as pediatric patients with acute lymphoblastic leukemia. However, a high rate of hypersensitivity with prolonged use has limited its utilization. Stenotrophomonas maltophilia (S. maltophilia) EMCC2297 isolate was reported as a novel and promising source for L- asparaginase. The present study aimed at the production, purification, and characterization of L- asparaginase from S. maltophilia EMCC2297 isolate. The microbial production of L-asparaginase by the test isolate could be increased by pre-exposure to chloramphenicol at 200 µg/ml concentration. S. maltophilia EMCC2297 L-asparaginase could be purified to homogeneity by ammonium sulphate precipitation and the purified form obtained by gel exclusion chromatography showed total activity of 96.4375 IU/ml and specific activity of 36.251 IU/mg protein. SDS-PAGE analysis revealed that the purified form of the enzyme is separated at an apparent molecular weight of 17 KDa. Michaelis-Menten constant analysis showed a Km value of 4.16 × 10- 2 M with L-asparagine as substrate and Vmax of 10.67 IU/ml. The antitumor activity of the purified enzyme was evaluated on different cell lines and revealed low IC50 of 2.2 IU/ml and 2.83 IU/ml for Hepatocellular cancer cell line (HepG-2), human leukemia cancer cell line (K-562), respectively whereas no cytotoxic effect could be detected on normal human lung fibroblast cells (MRC-5). However, mice treated with native L-asparaginase showed lower IgG titre compared to commercial L-asparaginase. This study highlights the promising characteristics of this enzyme making it a valuable candidate for further research and development to be an adduct in cancer chemotherapy.

Desirable L-asparaginases for treating cancer and current research trends

Amino acid depletion therapy is a promising approach for cancer treatment. It exploits the differences in the metabolic processes between healthy and cancerous cells. Certain microbial enzymes induce cancer cell apoptosis by removing essential amino acids. L-asparaginase is an enzyme approved by the FDA for the treatment of acute lymphoblastic leukemia. The enzymes currently employed in clinics come from two different sources: Escherichia coli and Erwinia chrysanthemi. Nevertheless, the search for improved enzymes and other sources continues because of several factors, including immunogenicity, in vivo instability, and protease degradation. Before determining whether L-asparaginase is clinically useful, research should consider the Michaelis constant, turnover number, and maximal velocity. The identification of L-asparaginase from microbial sources has been the subject of various studies. The primary goals of this review are to explore the most current approaches used in the search for therapeutically useful L-asparaginases and to establish whether these investigations identified the crucial characteristics of L-asparaginases before declaring their therapeutic potential.

Apoptosis and cell cycle arrest of leukemic cells by a robust and stable L-asparaginase from Pseudomonas sp. PCH199

Biomolecules obtained from microorganisms living in extreme environments possess properties that have pharmacokinetic advantages. Enzyme assay revealed recombinant L-ASNase, an extremozyme from Pseudomonas sp. PCH199 is to be highly stable with 90 % activity (200 h) at 37 °C. The stability of the enzyme in human serum (50 % activity maintained in 63 h) reveals high therapeutic potential with less dosage. The enzyme exhibited cytotoxicity to K562 blood cancer cell lines with IC50 of 0.37 U/mL without affecting the IEC-6 normal epithelial cell line. Due to the depletion of L-asparagine, K562 cells experience nutritional stress that results in the abruption of metabolic processes and eventually leads to apoptosis. Comparative studies on MCF-7 cells also revealed the same fate. Due to nutritional stress induced by L-ASNase treatment, mitochondrial membrane potential was lost, and reactive oxygen species were increased to 48 % (K562) and 21 % (MCF-7) as indicated by flow cytometric analysis. DAPI staining with prominent nuclear morphological changes visualized under the fluorescent microscope confirmed apoptosis in both cancer cells. Treatment increases pro-apoptotic Bax protein, and eventually, the cell cycle is arrested at the G2/M phase in both cell lines. Therefore, the current study paves the way for PCH199 L-ASNase to be considered a potential chemotherapeutic agent for treating acute lymphoblastic leukemia.

Dissecting dual specificity: Identifying key residues in L-asparaginase for enhanced acute lymphoid leukemia therapy and reduced adverse effects

L-asparaginase from Escherichia coli (EcA) has been used for the treatment of acute lymphoid leukemia (ALL) since the 1970s. Nevertheless, the enzyme has a second specificity that results in glutaminase breakdown, resulting in depletion from the patient's body, causing severe adverse effects. Despite the huge interest in the use of this enzyme, the exact process of glutamine depletion is still unknown and there is no consensus regarding L-asparagine hydrolysis. Here, we investigate the role of T12, Y25, and T89 in asparaginase and glutaminase activities. We obtained individual clones containing mutations in the T12, Y25 or T89 residues. After the recombinant production of wild-type and mutated EcA, The purified samples were subjected to structural analysis using Nano Differential Scanning Fluorimetry, which revealed that all samples contained thermostable molecules in their active structural conformation, the homotetramer conformation. The quaternary conformation was confirmed by DLS and SEC. The activity enzymatic assay combined with molecular dynamics simulation identified the contribution of T12, Y25, and T89 residues in EcA glutaminase and asparaginase activities. Our results mapped the enzymatic behavior paving the way for the designing of improved EcA enzymes, which is important in the treatment of ALL.

Characterization and applications of glutaminase free L-asparaginase from indigenous Bacillus halotolerans ASN9

L-asparaginase (L-ASNase) is a versatile anticancer and acrylamide reduction enzyme predominantly used in medical and food industries. However, the high specificity of L-asparaginase formulations for glutamine, low thermostability, and blood clearance are the major disadvantages. Present study describes production, characterization, and applications of glutaminase free extracellular L-asparaginase from indigenous Bacillus halotolerans ASN9 isolated from soil sample. L-asparaginase production was optimized in M9 medium (containing 0.2% sucrose and 1% L-asparagine) that yielded maximum L-ASNase with a specific activity of 256 U mg-1 at pH 6 and 37°C. L-asparaginase was purified through acetone precipitation and Sephadex G-100 column, yielding 48.9 and 24% recovery, respectively. Enzyme kinetics revealed a Vmax of 466 mM min-1 and Km of 0.097 mM. Purified L-ASNase showed no activity against glutamine. The purified glutaminase free L-ASNase has a molecular mass of 60 kDa and an optimum specific activity of 3083 U mg-1 at pH 7 and 37°C. The enzyme retains its activity and stability over a wide range of pH and temperature, in the presence of selected protein inhibitors (SDS, β-mercaptoethanol), CoCl2, KCl, and NaCl. The enzyme also exhibited antioxidant activity against DPPH radical (IC50 value 70.7 μg mL-1) and anticancer activity against U87 human malignant glioma (IC50 55 μg mL-1) and Huh7 human hepatocellular carcinoma (IC50 37 μg mL-1) cell lines. Normal human embryonic kidney cells (HEK293) had greater than 80% cell viability with purified L-ASNase indicating its least cytotoxicity against normal cells. The present work identified potent glutaminase free L-ASNase from B. halotolerans ASN9 that performs well in a wide range of environmental conditions indicating its suitability for various commercial applications.

Halomonas elongata: a microbial source of highly stable enzymes for applied biotechnology

Extremophilic microorganisms, which are resistant to extreme levels of temperature, salinity, pH, etc., have become popular tools for biotechnological applications. Due to their availability and cost-efficacy, enzymes from extremophiles are getting the attention of researchers and industries in the field of biocatalysis to catalyze diverse chemical reactions in a selective and sustainable manner. In this mini-review, we discuss the advantages of Halomonas elongata as moderate halophilic bacteria to provide suitable enzymes for biotechnology. While enzymes from H. elongata are more resistant to the presence of salt compared to their mesophilic counterparts, they are also easier to produce in heterologous hosts compared with more extremophilic microorganisms. Herein, a set of different enzymes (hydrolases, transferases, and oxidoreductases) from H. elongata are showcased, highlighting their interesting properties as more efficient and sustainable biocatalysts. With this, we aim to improve the visibility of halotolerant enzymes and their uncommon properties to integrate biocatalysis in industrial set-ups. KEYPOINTS: • Production and use of halotolerant enzymes can be easier than strong halophilic ones. • Enzymes from halotolerant organisms are robust catalysts under harsh conditions. • Halomonas elongata has shown a broad enzyme toolbox with biotechnology applications.

Biochemical characterization of extremozyme L-asparaginase from Pseudomonas sp. PCH199 for therapeutics

L-asparaginase (L-ASNase) from microbial sources is a commercially vital enzyme to treat acute lymphoblastic leukemia. However, the side effects associated with the commercial formulations of L-ASNases intrigued to explore for efficient and desired pharmacological enzymatic features. Here, we report the biochemical and cytotoxic evaluation of periplasmic L-ASNase of Pseudomonas sp. PCH199 isolated from the soil of Betula utilis, the Himalayan birch. L-ASNase production from wild-type PCH199 was enhanced by 2.2-fold using the Response Surface Methodology (RSM). Increased production of periplasmic L-ASNase was obtained using an optimized osmotic shock method followed by its purification. The purified L-ASNase was a monomer of 37.0 kDa with optimum activity at pH 8.5 and 60 ℃. It also showed thermostability retaining 100.0% (200 min) and 90.0% (70 min) of the activity at 37 and 50 ℃, respectively. The K_m and V_max values of the purified enzyme were 0.164 ± 0.009 mM and 54.78 ± 0.4 U/mg, respectively. L-ASNase was cytotoxic to the K562 blood cancer cell line (IC₅₀ value 0.309 U/mL) within 24 h resulting in apoptotic nuclear morphological changes as examined by DAPI staining. Therefore, the dynamic functionality in a wide range of pH and temperature and stability of PCH199 L-ASNase at 37 ℃ with cytotoxic potential proves to be pharmaceutically important for therapeutic application.

Characterization, Anti-proliferative Activity, and Bench-Scale Production of Novel pH-Stable and Thermotolerant L-Asparaginase from Bacillus licheniformis PPD37

Bacterial L-asparaginase (LA) is a chemotherapeutic drug that has remained mainstay of cancer treatment for several decades. LA has been extensively used worldwide for the treatment of acute lymphoblastic leukemia (ALL). A halotolerant bacterial strain Bacillus licheniformis sp. isolated from marine environment was used for LA production. The enzyme produced was subjected to purification and physico-chemical characterisation. Purified LA was thermotolerant and demonstrated more than 90% enzyme activity after 1 h of incubation at 80 °C. LA has also proved to be resistant against pH gradient and retained activity at pH ranging from 3.0 to 10. The enzyme also had high salinity tolerance with 90% LA activity at 10% NaCl concentration. Detergents like Triton X-100 and Tween-80 were observed to inhibit LA activity while more than 70% catalytic activity was maintained in the presence of metals. Electrophoretic analysis revealed that LA is a heterodimer (~ 63 and ~ 65 kDa) and has molecular mass of around 130 kDa in native form. The kinetic parameters of LA were tested with LA having low K_m value of 1.518 µM and V_max value of 6.94 µM/min/mL. Purified LA has also exhibited noteworthy antiproliferative activity against cancer cell lines-HeLa, SiHa, A549, and SH-SY-5Y. In addition, bench-scale LA production was conducted in a 5-L bioreactor using moringa leaves as cost-effective substrate.

Molecular cloning, characterization, and in-silico analysis of l-asparaginase from Himalayan Pseudomonas sp. PCH44

l-Asparaginase (l-ASNase) is a key enzyme used to treat acute lymphoblastic leukemia, a childhood blood cancer. Here, we report on the characterization of a recombinant l-ASNase (Ps44-asn II) from Pseudomonas sp. PCH44. The gene was identified from its genome, cloned, and overexpressed in the host Escherichia coli (E. coli). The recombinant l-ASNase (Ps44-ASNase II) was purified with a monomer size of 37.0 kDa and a homotetrameric size of 148.0 kDa. The purified Ps44-ASNase II exhibited optimum activity of 40.84 U/mg in Tris-HCl buffer (50 mM, pH 8.5) at 45 °C for 15 min. It retained 76.53% of enzyme activity at 45 °C after 120 min of incubation. The half-life and K _d values were 600 min and 1.10 × 10^-3 min^-1, respectively, at 45 °C. The kinetic constants values K _m and V _max were 0.56, 0.728 mM, and 29.41, 50.12 U/mg for l-asparagine and l-glutamine, respectively. However, k _cat for l-glutamine is more (30.91 s^-1) than l-asparagine (18.06 s^-1), suggesting that enzymes act more efficiently on l-glutamine than l-asparagine. The docking analysis of l-asparagine and l-glutamine with active site residues of the enzyme revealed a molecular basis for high l-glutaminase (L-GLNase) activity and provided insights into the role of key amino acid residues in the preferential enzymatic activities.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03224-0.

Biochemical and Biological Evaluation of an L-Asparaginase from Isolated Escherichia coli MF-107 as an Anti-Tumor Enzyme on MCF7 Cell Line

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Appraisal of cytotoxicity and acrylamide mitigation potential of L-asparaginase SlpA from fish gut microbiome

L-asparaginase catalyzes the hydrolysis of L-asparagine to L-aspartic acid and ammonia. It has application in the treatment of acute lymphoblastic leukemia in children, as well as in other malignancies, in addition to its role as a food processing aid for the mitigation of acrylamide formation in the baking industry. Its use in cancer chemotherapy is limited due to problems such as its intrinsic glutaminase activity and associated side effects, leading to an increased interest in the search for novel L-asparaginases without L-glutaminase activity. This study reports the cloning and expression of an L-asparaginase contig obtained from whole metagenome shotgun sequencing of Sardinella longiceps gut microbiota. Purified recombinant glutaminase-free L-asparaginase SlpA was a 74 kDa homodimer, with maximal activity at pH 8 and 30 °C. K_m and V_max of SlpA were determined to be 3.008 mM and 0.014 mM/min, respectively. SlpA displayed cytotoxic activity against K-562 (chronic myeloid leukemia) and MCF-7 (breast cancer) cell lines with IC₅₀ values of 0.3443 and 2.692 U/mL, respectively. SlpA did not show any cytotoxic activity against normal lymphocytes and was proved to be hemocompatible. Pre-treatment of biscuit and bread dough with different concentrations of SlpA resulted in a clear, dose-dependent reduction of acrylamide formation during baking. KEY POINTS: • Cloned and expressed L-asparaginase (SlpA) from fish gut microbiota • Purified SlpA displayed good cytotoxicity against K-562 and MCF-7 cell lines • SlpA addition caused a significant reduction of acrylamide formation during baking.

A critical review on exploitation of agro-industrial biomass as substrates for the therapeutic microbial enzymes production and implemented protein purification techniques

Annually, a huge amount of waste is generated by the industries that use agricultural biomass. Researchers have looked into employing this cheap and renewable agro-biomass as a substrate for enzyme production via fermentation processes to meet the ever-increasing worldwide need. Although there are a number of sources for enzyme extraction, microbial sources have dominated industrial sectors due to their easy availability and rapid growth. Microbial enzymes are currently used in a variety of industries, including pharmaceuticals, food, biofuels, textiles, paper, detergents, and so on, and using these nutritious feedstocks not only reduces production costs but also helps to reduce environmental concerns. The present review focuses on the therapeutic microbial enzymes produced using different agro-industrial biomass as raw materials, with down-streaming techniques for obtaining a final pure product. Additionally, the article also discussed biomass pretreatment processes, including physical, chemical and biological. The type of pretreatment method to be used is mostly governed by the intended use of the major molecular components of biomass (cellulose, hemicelluloses and lignin). Finally, purification challenges are included. All of this information will be useful in the industrial synthesis of high-purity targeted enzymes if the crucial aspects that have been discussed are taken into account.

Novel Insights on the Use of L-Asparaginase as an Efficient and Safe Anti-Cancer Therapy

Simple Summary

L-asparaginase (L-ASNase) therapy is key for achieving the very high cure rate of pediatric acute lymphoblastic leukemia (ALL), yet its use is mostly confined to this indication. One main reason preventing the expansion of today’s FDA-approved L-ASNases to solid cancers is their high toxicity and side effects, which become especially challenging in adult patients. The design of optimized L-ASNase molecules provides opportunities to overcome these unwanted toxicities. An additional challenge to broader application of L-ASNases is how cells can counter the pharmacological effect of this drug and the identification of L-ASNases resistance mechanisms. In this review, we discuss recent insights into L-ASNase adverse effects, resistance mechanisms, and how novel L-ASNase variants and drug combinations can expand its clinical applicability, with a focus on both hematological and solid tumors.

Abstract

L-Asparaginase (L-ASNase) is an enzyme that hydrolyses the amino acid asparagine into aspartic acid and ammonia. Systemic administration of bacterial L-ASNase is successfully used to lower the bioavailability of this non-essential amino acid and to eradicate rapidly proliferating cancer cells with a high demand for exogenous asparagine. Currently, it is a cornerstone drug in the treatment of the most common pediatric cancer, acute lymphoblastic leukemia (ALL). Since these lymphoblasts lack the expression of asparagine synthetase (ASNS), these cells depend on the uptake of extracellular asparagine for survival. Interestingly, recent reports have illustrated that L-ASNase may also have clinical potential for the treatment of other aggressive subtypes of hematological or solid cancers. However, immunogenic and other severe adverse side effects limit optimal clinical use and often lead to treatment discontinuation. The design of optimized and novel L-ASNase formulations provides opportunities to overcome these limitations. In addition, identification of multiple L-ASNase resistance mechanisms, including ASNS promoter reactivation and desensitization, has fueled research into promising novel drug combinations to overcome chemoresistance. In this review, we discuss recent insights into L-ASNase adverse effects, resistance both in hematological and solid tumors, and how novel L-ASNase variants and drug combinations can expand its clinical applicability.

Microbial L-asparaginase for Application in Acrylamide Mitigation from Food: Current Research Status and Future Perspectives

L-asparaginase (E.C.3.5.1.1) hydrolyzes L-asparagine to L-aspartic acid and ammonia, which has been widely applied in the pharmaceutical and food industries. Microbes have advantages for L-asparaginase production, and there are several commercially available forms of L-asparaginase, all of which are derived from microbes. Generally, L-asparaginase has an optimum pH range of 5.0-9.0 and an optimum temperature of between 30 and 60 °C. However, the optimum temperature of L-asparaginase from hyperthermophilic archaea is considerable higher (between 85 and 100 °C). The native properties of the enzymes can be enhanced by using immobilization techniques. The stability and recyclability of immobilized enzymes makes them more suitable for food applications. This current work describes the classification, catalytic mechanism, production, purification, and immobilization of microbial L-asparaginase, focusing on its application as an effective reducer of acrylamide in fried potato products, bakery products, and coffee. This highlights the prospects of cost-effective L-asparaginase, thermostable L-asparaginase, and immobilized L-asparaginase as good candidates for food application in the future.

Structural and biochemical properties of L-asparaginase

l-Asparaginase (a hydrolase converting l-asparagine to l-aspartic acid) was the first enzyme to be used in clinical practice as an anticancer agent after its approval in 1978 as a component of a treatment protocol for childhood acute lymphoblastic leukemia. Structural and biochemical properties of l-asparaginases have been extensively investigated during the last half-century, providing an accurate structural description of the enzyme isolated from a variety of sources, as well as clarifying the mechanism of its activity. This review provides a critical assessment of the current state of knowledge of primarily structural, but also selected biochemical properties of 'bacterial-type' l-asparaginases from different organisms. The most extensively studied members of this enzyme family are l-asparaginases highly homologous to one of the two enzymes from Escherichia coli (usually referred to as EcAI and EcAII). Members of this enzyme family, although often called bacterial-type l-asparaginases, have been also identified in such divergent organisms as archaea or eukarya. Over 100 structural models of l-asparaginases have been deposited in the Protein Data Bank during the last 30 years. One of the prime achievements of structure-centered approaches was the elucidation of the details of the mechanism of enzymatic action of this unique hydrolase that utilizes a side chain of threonine as the primary nucleophile. The molecular basis of other important properties of these enzymes, such as their substrate specificity, is still being evaluated. Results of structural and mechanistic studies of l-asparaginases are being utilized in efforts to improve the clinical properties of this important anticancer drug.

Non-classical secretion of a type I L-asparaginase in Bacillus subtilis

L-asparaginase (EC 3.5.1.1) showed great commercial value owing to its effective treatment of acute lymphoblastic leukemia (ALL), lymphoid system malignancies and Hodgkin disease, and also to its use in the prevention of acrylamide formation in fried and baked foods. In this study, a type I L-asparaginase gene from Bacillus licheniformis Z-1 (BlAase) was cloned and expressed in Bacillus subtilis RIK 1285. Results showed that even without the mediation of any N-terminal signal peptides, BlAase can efficiently secrete into the medium. Further investigation indicated that the secretion of the BlAase was via neither Sec- nor Tat-dependent secretion pathway, and both the N- and C-terminal regions of the BlAase were essential for its expression and secretion, implying that BlAase might be secreted via a non-classical secretion pathway. To explore its secretion ability, BlAase was used as a signal peptide to direct the secretion of various heterologous proteins, where two of five proteins were successfully secreted with the mediation of BlAase. To the best of our knowledge, this is the first time to achieve extracellular expression of L-asparaginase via non-classical protein secretion pathway in B. subtilis, and provide a potential tool for secretion of recombinant proteins expressed in B. subtilis using BlAase as a signal peptide.

Metagenomic discovery and functional validation of L-asparaginases with anti-leukemic effect from the Caspian Sea

By screening 27,000 publicly available prokaryotic genomes, we recovered ca. 6300 type I and ca. 5200 type II putative L-asparaginase highlighting the vast potential of prokaryotes. Caspian water with similar salt composition to the human serum was targeted for in silico L-asparaginase screening. We screened ca. three million predicted genes of its assembled metagenomes that resulted in annotation of 87 putative L-asparaginase genes. The L-asparagine hydrolysis was experimentally confirmed by synthesizing and cloning three selected genes in E. coli. Catalytic parameters of the purified enzymes were determined to be among the most desirable reported values. Two recombinant enzymes represented remarkable anti-proliferative activity (IC50 <1IU/ml) against leukemia cell line Jurkat while no cytotoxic effect on human erythrocytes or human umbilical vein endothelial cells was detected. Similar salinity and ionic concentration of the Caspian water to the human serum highlights the potential of secretory L-asparaginases recovered from these metagenomes as potential treatment agents.

Development of Processes for Recombinant L-Asparaginase II Production by Escherichia coli Bl21 (De3): From Shaker to Bioreactors

Since 1961, L-asparaginase has been used to treat patients with acute lymphocytic leukemia. It rapidly depletes the plasma asparagine and deprives the blood cells of this circulating amino acid, essential for the metabolic cycles of cells. In the search for viable alternatives to produce L-asparaginase, this work aimed to produce this enzyme from Escherichia coli in a shaker and in a 3 L bioreactor. Three culture media were tested: defined, semi-defined and complex medium. L-asparaginase activity was quantified using the β-hydroxamate aspartic acid method. The defined medium provided the highest L-asparaginase activity. In induction studies, two inducers, lactose and its analog IPTG, were compared. Lactose was chosen as an inducer for the experiments conducted in the bioreactor due to its natural source, lower cost and lower toxicity. Batch and fed-batch cultures were carried out to reach high cell density and then start the induction. Batch cultivation provided a final cell concentration of 11 g L-1 and fed-batch cultivation produced 69.90 g L-1 of cells, which produced a volumetric activity of 43,954.79 U L-1 after lactose induction. L-asparaginase was produced in a shaker and scaled up to a bioreactor, increasing 23-fold the cell concentration and thus, the enzyme productivity.

Recent Strategies and Applications for l-Asparaginase Confinement

l-asparaginase (ASNase, EC 3.5.1.1) is an aminohydrolase enzyme with important uses in the therapeutic/pharmaceutical and food industries. Its main applications are as an anticancer drug, mostly for acute lymphoblastic leukaemia (ALL) treatment, and in acrylamide reduction when starch-rich foods are cooked at temperatures above 100 °C. Its use as a biosensor for asparagine in both industries has also been reported. However, there are certain challenges associated with ASNase applications. Depending on the ASNase source, the major challenges of its pharmaceutical application are the hypersensitivity reactions that it causes in ALL patients and its short half-life and fast plasma clearance in the blood system by native proteases. In addition, ASNase is generally unstable and it is a thermolabile enzyme, which also hinders its application in the food sector. These drawbacks have been overcome by the ASNase confinement in different (nano)materials through distinct techniques, such as physical adsorption, covalent attachment and entrapment. Overall, this review describes the most recent strategies reported for ASNase confinement in numerous (nano)materials, highlighting its improved properties, especially specificity, half-life enhancement and thermal and operational stability improvement, allowing its reuse, increased proteolysis resistance and immunogenicity elimination. The most recent applications of confined ASNase in nanomaterials are reviewed for the first time, simultaneously providing prospects in the described fields of application.

Functional and structural evaluation of the antileukaemic enzyme L-asparaginase II expressed at low temperature by different Escherichia coli strains

Acute lymphoblastic leukaemia (ALL) affects lymphoblastic cells and is the most common neoplasm during childhood. Among the pharmaceuticals used in the treatment protocols for ALL, Asparaginase (ASNase) from Escherichia coli (EcAII) is an essential biodrug. Meanwhile, the use of EcAII in neoplastic treatments causes several side effects, such as immunological reactions, hepatotoxicity, neurotoxicity, depression, and coagulation abnormalities. Commercial EcAII is expressed as a recombinant protein, similar to novel enzymes from different organisms; in fact, EcAII is a tetrameric enzyme with high molecular weight (140 kDa), and its overexpression in recombinant systems often results in bacterial cell death or the production of aggregated or inactive EcAII protein, which is related to the formation of inclusion bodies. On the other hand, several commercial expression strains have been developed to overcome these expression issues, but no studies on a systematic evaluation of the E. coli strains aiming to express recombinant asparaginases have been performed to date. In this study, we evaluated eleven expression strains at a low temperature (16 °C) with different characteristics to determine which is the most appropriate for asparaginase expression; recombinant wild-type EcAII (rEcAII) was used as a prototype enzyme and the secondary structure content, oligomeric state, aggregation and specific activity of the enzymes were assessed. Structural analysis suggested that a correctly folded tetrameric rEcAII was obtained using ArcticExpress (DE3), a strain that co-express chaperonins, while all other strains produced poorly folded proteins. Additionally, the enzymatic assays showed high specific activity of proteins expressed by ArcticExpress (DE3) when compared to the other strains used in this work.

Halophiles and Their Biomolecules: Recent Advances and Future Applications in Biomedicine

The organisms thriving under extreme conditions better than any other organism living on Earth, fascinate by their hostile growing parameters, physiological features, and their production of valuable bioactive metabolites. This is the case of microorganisms (bacteria, archaea, and fungi) that grow optimally at high salinities and are able to produce biomolecules of pharmaceutical interest for therapeutic applications. As along as the microbiota is being approached by massive sequencing, novel insights are revealing the environmental conditions on which the compounds are produced in the microbial community without more stress than sharing the same substratum with their peers, the salt. In this review are reported the molecules described and produced by halophilic microorganisms with a spectrum of action in vitro: antimicrobial and anticancer. The action mechanisms of these molecules, the urgent need to introduce alternative lead compounds and the current aspects on the exploitation and its limitations are discussed.

Vascular tissue engineering: Fabrication and characterization of acetylsalicylic acid-loaded electrospun scaffolds coated with amniotic membrane lysate

As the incidence of small-diameter vascular graft (SDVG) occlusion is considerably high, a great amount of research is focused on constructing a more biocompatible graft. The absence of a biocompatible surface in the lumen of the engineered grafts that can support confluent lining with endothelial cells (ECs) can cause thrombosis and graft failure. Blood clot formation is mainly because of the lack of an integrated endothelium. The most effective approach to combat this problem would be using natural extracellular matrix constituents as a mimic of endothelial basement membrane along with applying anticoagulant agents to provide local antithrombotic effects. In this study, we fabricated aligned and random electrospun poly-L-lactic acid (PLLA) scaffolds containing acetylsalicylic acid (ASA) as the anticoagulation agent and surface coated them with amniotic membrane (AM) lysate. Vascular scaffolds were structurally and mechanically characterized and assessed for cyto- and hemocompatibility and their ability to support endothelial differentiation was examined. All the scaffolds showed appropriate tensile strength as expected for vascular grafts. Lack of cytotoxicity, cellular attachment, growth, and infiltration were proved using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and scanning electron microscopy. The blood compatibilities of different scaffolds examined by in vitro hemolysis and blood coagulation assays elucidated the excellent hemocompatibility of our novel AM-coated ASA-loaded nanofibers. Drug-loaded scaffolds showed a sustained release profile of ASA in 7 days. AM-coated electrospun PLLA fibers showed enhanced cytocompatibility for human umbilical vein ECs, making a confluent endothelial-like lining. In addition, AM lysate-coated ASA-PLLA-aligned scaffold proved to support endothelial differentiation of Wharton's jelly-derived mesenchymal stem cells. Our results together indicated that AM lysate-coated ASA releasing scaffolds have promising potentials for development of a biocompatible SDVG.

Optimized chromogenic dyes-based identification and quantitative evaluation of bacterial l-asparaginase with low/no glutaminase activity bioprospected from pristine niches in Indian trans-Himalaya

Here, we report on the isolation of bacterial isolates from Himalayan niches, which produced extracellular l-asparaginase with low/no glutaminase activity. From the 235 isolates, 85 asparaginase positive bacterial isolates were identified by qualitative screening using optimized chromogenic dyes assay. Optimized concentration of different dyes revealed maximum color visualization in phenol red (0.003%). The diversity analysis of asparaginase positive isolates revealed that Proteobacteria (83%) are the most dominant, followed by Actinobacteria (12%), Firmicutes (3%), and Bacteriodetes (2%). Eleven isolates, which represented seven Pseudomonas species, one species each of the genus Arthrobacter, Janthinobacterium, Lelliottia, and Rahnella, were selected for further studies based on highest zone ratio and novel aspects for l-asparaginase production. Of these, five isolates, namely, Pseudomonas sp. PCH133, Pseudomonas sp. PCH146, Pseudomonas sp. PCH182, Rahnella sp. PCH162, and Arthrobacter sp. PCH138, produced l-asparaginase without glutaminase activity after 55 h of growth with the former isolate showing the highest l-asparaginase activity (1.67 U/ml). Interestingly, this is the first report of l-asparaginase production by members of the genera Janthinobacterium, Rahnella, and Lelliottia.

pH-Dependent Thermal Stability of Vibrio cholerae L-asparaginase

BACKGROUND

pH is one of the decisive macromolecular properties of proteins that significantly affects enzyme structure, stability and reaction rate. Change in pH may protonate or deprotonate the side group of aminoacid residues in the protein, thereby resulting in changes in chemical and structural features. Hence studies on the kinetics of enzyme deactivation by pH are important for assessing the bio-functionality of industrial enzymes. L-asparaginase is one such important enzyme that has potent applications in cancer therapy and food industry.

OBJECTIVE

The objective of the study is to understand and analyze the influence of pH on deactivation and stability of Vibrio cholerae L-asparaginase.

METHODS

Kinetic studies were conducted to analyze the effect of pH on stability and deactivation of Vibrio cholerae L-asparaginase. Circular Dichroism (CD) and Differential Scanning Calorimetry (DSC) studies have been carried out to understand the pH-dependent conformational changes in the secondary structure of V. cholerae L-asparaginase.

RESULTS

The enzyme was found to be least stable at extreme acidic conditions (pH< 4.5) and exhibited a gradual increase in melting temperature from 40 to 81 °C within pH range of 4.0 to 7.0. Thermodynamic properties of protein were estimated and at pH 7.0 the protein exhibited ΔG37of 26.31 kcal mole-1, ΔH of 204.27 kcal mole-1 and ΔS of 574.06 cal mole-1 K-1.

CONCLUSION

The stability and thermodynamic analysis revealed that V. cholerae L-asparaginase was highly stable over a wide range of pH, with the highest stability in the pH range of 5.0-7.0.

Recombinant l-Asparaginase II from Lactobacillus casei subsp. casei ATCC 393 and Its Anticancer Activity

l-asparaginases from bacterial origin are employed extensively in leukemic treatment and food industry. The present study focuses on the characterization of the recombinant l-asparaginase II from Lactobacillus casei subsp. casei ATCC 393 cloned into Escherichia coli expression system and purified using Ni-NTA chromatography. The recombinant l-asparaginase as a monomer had a molecular weight of 35 kDa. The enzyme was active from 10 to 80 °C with the optimum at 40 °C. The enzyme retained its activity at 28 °C and 37 °C up to 24 h. The enzyme had optimum pH of 6 and retained 50% activity till 18 h. The K_m of the recombinant enzyme was 0.01235 mM and V_max 1.576 mM/min. The half life of recombinant l-asparaginase II in human serum was 44 h and trypsin was for 15 min. The LC-MS/MS analysis revealed the molecular weight of 35,050 and pI of 5.64. The secondary structure prediction using CD spectroscopy for the recombinant enzyme showed 33.5% α-helix, 66.5% turn and 0% β sheets. The cytotoxicity of the recombinant enzyme was analysed against MOLT 3, Jurkat E6.1 and K-562 with the IC 50 value of 30, 62.5 and 50 µg/ml.

Production and Anticancer Activity of an L-Asparaginase from Bacillus licheniformis Isolated from the Red Sea, Saudi Arabia

Microbial L-asparaginase (ASNase) is an important anticancer agent that is used extensively worldwide. In this study, 40 bacterial isolates were obtained from the Red Sea of Saudi Arabia and screened for ASNase production using a qualitative rapid plate assay, 28 of which were producing large L-asparagine hydrolysis zones. The ASNase production of the immobilized bacterial cells was more favorable than that of freely suspended cells. A promising isolate, KKU-KH14, was identified by 16S rRNA gene sequencing as Bacillus licheniformis. Maximal ASNase production was achieved using an incubation period of 72 h, with an optimum of pH 6.5, an incubation temperature of 37 °C, an agitation rate 250 rpm, and with glucose and (NH4)2SO4 used as the carbon and nitrogen sources, respectively. The glutaminase activity was not detected in the ASNase preparations. The purified ASNase showed a final specific activity of 36.08 U/mg, and the molecular weight was found to be 37 kDa by SDS-PAGE analysis. The maximum activity and stability of the purified enzyme occurred at pH values of 7.5 and 8.5, respectively, with maximum activity at 37 °C and complete thermal stability at 70 °C for 1 h. The Km and Vmax values of the purified enzyme were 0.049995 M and of 45.45 μmol/ml/min, respectively. The anticancer activity of the purified ASNase showed significant toxic activity toward HepG-2 cells (IC50 11.66 µg/mL), which was greater than that observed against MCF-7 (IC50 14.55 µg/mL) and HCT-116 cells (IC50 17.02 µg/mL). The results demonstrated that the Red Sea is a promising biological reservoir, as shown by the isolation of B. licheniformis, which produces a glutaminase free ASNase and may be a potential candidate for further pharmaceutical use as an anticancer drug.