Two L-asparaginases from Escherichia coli B. Their separation, purification, and antitumor activity

Probing the active site of Class 3 L-asparaginase by mutagenesis. I. Tinkering with the zinc coordination site of ReAV

ReAV, the inducible Class-3 L-asparaginase from the nitrogen-fixing symbiotic bacterium Rhizobium etli, is an interesting candidate for optimizing its enzymatic potential for antileukemic applications. Since it has no structural similarity to known enzymes with this activity, it may offer completely new ways of approach. Also, as an unrelated protein, it would evade the immunological response elicited by other asparaginases. The crystal structure of ReAV revealed a uniquely assembled protein homodimer with a highly specific C135/K138/C189 zinc binding site in each subunit. It was also shown before that the Zn2+ cation at low and optimal concentration boosts the ReAV activity and improves substrate specificity, which indicates its role in substrate recognition. However, the detailed catalytic mechanism of ReAV is still unknown. In this work, we have applied site-directed mutagenesis coupled with enzymatic assays and X-ray structural analysis to elucidate the role of the residues in the zinc coordination sphere in catalysis. Almost all of the seven ReAV muteins created in this campaign lost the ability to hydrolyze L-asparagine, confirming our predictions about the significance of the selected residues in substrate hydrolysis. We were able to crystallize five of the ReAV mutants and solve their crystal structures, revealing some intriguing changes in the active site area as a result of the mutations. With alanine substitutions of Cys135 or Cys189, the zinc coordination site fell apart and the mutants were unable to bind the Zn2+ cation. Moreover, the absence of Lys138 induced atomic shifts and conformational changes of the neighboring residues from two active-site Ser-Lys tandems. Ser48 from one of the tandems, which is hypothesized to be the catalytic nucleophile, usually changes its hydration pattern in response to the mutations. Taken together, the results provide many useful clues about the catalytic mechanism of the enzyme, allowing one to cautiously postulate a possible enzymatic scenario.

Biochemical characterization of glutaminase-free L-asparaginases from Himalayan Pseudomonas and Rahnella spp. for acrylamide mitigation

L-asparaginase having low glutaminase activity is important in clinical and food applications. Herein, glutaminase-free L-asparaginase (type I) coding genes from Pseudomonas sp. PCH182 (Ps-ASNase I) and Rahnella sp. PCH162 (Rs-ASNase I) was amplified using gene-specific primers, cloned into a pET-47b(+) vector, and plasmids were transformed into Escherichia coli (E. coli). Further, affinity chromatography purified recombinant proteins to homogeneity with monomer sizes of ~37.0 kDa. Purified Ps-ASNase I and Rs-ASNase I were active at wide pHs and temperatures with optimum activity at 50 °C (492 ± 5 U/mg) and 37 °C (308 ± 4 U/mg), respectively. Kinetic constant Km and Vmax for L-asparagine (Asn) were 2.7 ± 0.06 mM and 526.31 ± 4.0 U/mg for Ps-ASNase I, and 4.43 ± 1.06 mM and 434.78 ± 4.0 U/mg for Rs-ASNase I. Circular dichroism study revealed 29.3 % and 24.12 % α-helix structures in Ps-ASNase I and Rs-ASNase I, respectively. Upon their evaluation to mitigate acrylamide formation, 43 % and 34 % acrylamide (AA) reduction were achieved after pre-treatment of raw potato slices, consistent with 65 % and 59 % Asn reduction for Ps-ASNase I and Rs-ASNase I, respectively. Current findings suggested the potential of less explored intracellular L-asparaginase in AA mitigation for food safety.

Mutations in asparaginase II from E. coli and implications for inactivation and PEGylation

All clinically-used asparaginases convert L-asparagine (L-Asn) to l-aspartate (L-Asp) and l-glutamine (L-Gln) to L-glutamate (L-Glu), which has been useful in reducing bioavailable asparagine and glutamine in patients under treatment for acute lymphoblastic leukemia. The E. coli type 2 L-asparaginase (EcA2) can present different sequences among varying bacterial strains, which we hypothesized that might affect their biological function, stability and interchangeability. Here we report the analysis of two EcA2 provided by the public health system of a middle-income country. These enzymes were reported to have similar specific activity in vitro, whereas they differ in vivo. Protein sequencing by LC-MS-MS and peptide mapping by MALDI-ToF-MS of their tryptic digests revealed that Aginasa™ share similar sequence to EcA2 from E. coli strain BL21(DE3), while Leuginase™ has sequence equivalent to EcA2 from E. coli strain AS1.357. The two amino acid differences between Aginasa™ (64D and 252 T) and Leuginase™ (64 N and 252S) resulted in structural divergences in solution as accessed by small-angle X-ray scattering and molecular dynamics simulation trajectories. The conformational variability further results in dissimilar surface accessibility with major consequences for PEGylation, as well as different susceptibility to degradation by limited proteolysis. The present results reveal that the sequence variations between these two EcA2 variants results in conformational changes associated with differential conformational plasticity, potentially affecting physico-chemical and biological properties, including proteolytic and immunogenic silent inactivation.

Interactions between gut microbiota and Parkinson's disease: The role of microbiota-derived amino acid metabolism

Non-motor symptoms (NMS) of Parkinson's disease (PD), such as constipation, sleep disorders, and olfactory deficits, may emerge up to 20 years earlier than motor symptoms. A series of evidence indicates that the pathology of PD may occur from the gastrointestinal tract to the brain. Numerous studies support that the gut microbiota communicates with the brain through the immune system, special amino acid metabolism, and the nervous system in PD. Recently, there is growing recognition that the gut microbiota plays a vital role in the modulation of multiple neurochemical pathways via the “gut microbiota-brain axis” (GMBA). Many gut microbiota metabolites, such as fatty acids, amino acids, and bile acids, convey signaling functions as they mediate the crosstalk between gut microbiota and host physiology. Amino acids' abundance and species alteration, including glutamate and tryptophan, may disturb the signaling transmission between nerve cells and disrupt the normal basal ganglia function in PD. Specific amino acids and their receptors are considered new potential targets for ameliorating PD. The present study aimed to systematically summarize all available evidence on the gut microbiota-derived amino acid metabolism alterations associated with PD.

Targeting amino acid metabolism in cancer

Metabolic rewiring is a characteristic hallmark of cancer cells. This phenomenon sustains uncontrolled proliferation and resistance to apoptosis by increasing nutrients and energy supply. However, reprogramming comes together with vulnerabilities that can be used against tumor and can be applied in targeted therapy. In the last years, the genetic background of tumors has been identified thoroughly and new therapies targeting those mutations tested. Nevertheless, we propose that targeting the phenotype of cancer cells could be another way of treatment aiming to avoid drug resistance and non-responsiveness of cancer patients. Amino acid metabolism is part of the altered processes in cancer cells. Amino acids are building blocks and also sensors of signaling pathways regulating main biological processes. In this comprehensive review, we described four amino acids (asparagine, arginine, methionine, and cysteine) which have been actively investigated as potential targets for anti-tumor therapy. Asparagine depletion is successfully used for decades in the treatment of acute lymphoblastic leukemia and there is a strong implication to apply it to other types of tumors. Arginine auxotrophic tumors are great candidates for arginine-starvation therapy. Higher requirement for essential amino acids such as methionine and cysteine point out promising targetable weaknesses of cancer cells.

Overview of the structure, side effects, and activity assays of l-asparaginase as a therapy drug of acute lymphoblastic leukemia

l-Asparaginase (l-ASNase is the abbreviation, l-asparagine aminohydrolase, E.C.3.5.1.1) is an enzyme that is clinically employed as an antitumor agent for the treatment of acute lymphoblastic leukemia (ALL). Although l-ASNase is known to deplete l-asparagine (l-Asn), causing cytotoxicity in leukemia cells, the specific molecular signaling pathways are not well defined. Because of the deficiencies in the production and administration of current formulations, the l-ASNase agent in clinical use is still associated with serious side effects, so controlling its dose and activity monitoring during therapy is crucial for improving the treatment success rate. Accordingly, it is urgent to summarize and develop effective analytical methods to detect l-ASNase activity in treatment. However, current reports on these detection methods are fragmented and also have not been systematically summarized and classified, thereby not only delaying the investigations of specific molecular mechanisms, but also hindering the development of novel detection methods. Herein, in this review, we provided a detailed summary of the l-ASNase structures, antitumor mechanism and side effects, and current detection approaches, such as fluorescence assays, colorimetric assays, spectroscopic assays and some other assays. All of them possess unique advantages and disadvantages, so it has been difficult to establish clear criteria for clinical application. We hope that this review will be of some value in promoting the development of l-ASNase activity detection methods.

Selection of the Optimal L-asparaginase II Against Acute Lymphoblastic Leukemia: An In Silico Approach

BACKGROUND

L-asparaginase II (asnB), a periplasmic protein commercially extracted from E coli and Erwinia, is often used to treat acute lymphoblastic leukemia. L-asparaginase is an enzyme that converts L-asparagine to aspartic acid and ammonia. Cancer cells are dependent on asparagine from other sources for growth, and when these cells are deprived of asparagine by the action of the enzyme, the cancer cells selectively die.

OBJECTIVE

Questions remain as to whether asnB from E coli and Erwinia is the best asparaginase as they have many side effects. asnBs with the lowest Michaelis constant (Km; most potent) and lowest immunogenicity are considered the most optimal enzymes. In this paper, we have attempted the development of a method to screen for optimal enzymes that are better than commercially available enzymes.

METHODS

In this paper, the asnB sequence of E coli was used to search for homologous proteins in different bacterial and archaeal phyla, and a maximum likelihood phylogenetic tree was constructed. The sequences that are most distant from E coli and Erwinia were considered the best candidates in terms of immunogenicity and were chosen for further processing. The structures of these proteins were built by homology modeling, and asparagine was docked with these proteins to calculate the binding energy.

RESULTS

asnBs from Streptomyces griseus, Streptomyces venezuelae, and Streptomyces collinus were found to have the highest binding energy (-5.3 kcal/mol, -5.2 kcal/mol, and -5.3 kcal/mol, respectively; higher than the E coli and Erwinia asnBs) and were predicted to have the lowest Kms, as we found that there is an inverse relationship between binding energy and Km. Besides predicting the most optimal asparaginase, this technique can also be used to predict the most optimal enzymes where the substrate is known and the structure of one of the homologs is solved.

CONCLUSIONS

We have devised an in silico method to predict the enzyme kinetics from a sequence of an enzyme along with being able to screen for optimal alternative asnBs against acute lymphoblastic leukemia.

Structural and biophysical aspects of l-asparaginases: a growing family with amazing diversity

l-Asparaginases have remained an intriguing research topic since their discovery ∼120 years ago, especially after their introduction in the 1960s as very efficient antileukemic drugs. In addition to bacterial asparaginases, which are still used to treat childhood leukemia, enzymes of plant and mammalian origin are now also known. They have all been structurally characterized by crystallography, in some cases at outstanding resolution. The structural data have also shed light on the mechanistic details of these deceptively simple enzymes. Yet, despite all this progress, no better therapeutic agents have been found to beat bacterial asparaginases. However, a new option might arise with the discovery of yet another type of asparaginase, those from symbiotic nitrogen-fixing Rhizobia, and with progress in the protein engineering of enzymes with desired properties. This review surveys the field of structural biology of l-asparaginases, focusing on the mechanistic aspects of the well established types and speculating about the potential of the new members of this amazingly diversified family.

Gastrointestinal Interaction between Dietary Amino Acids and Gut Microbiota: With Special Emphasis on Host Nutrition

The gastrointestinal tract (GIT) of humans and animals is host to a complex community of different microorganisms whose activities significantly influence host nutrition and health through enhanced metabolic capabilities, protection against pathogens, and regulation of the gastrointestinal development and immune system. New molecular technologies and concepts have revealed distinct interactions between the gut microbiota and dietary amino acids (AAs) especially in relation to AA metabolism and utilization in resident bacteria in the digestive tract, and these interactions may play significant roles in host nutrition and health as well as the efficiency of dietary AA supplementation. After the protein is digested and AAs and peptides are absorbed in the small intestine, significant levels of endogenous and exogenous nitrogenous compounds enter the large intestine through the ileocaecal junction. Once they move in the colonic lumen, these compounds are not markedly absorbed by the large intestinal mucosa, but undergo intense proteolysis by colonic microbiota leading to the release of peptides and AAs and result in the production of numerous bacterial metabolites such as ammonia, amines, short-chain fatty acids (SCFAs), branched-chain fatty acids (BCFAs), hydrogen sulfide, organic acids, and phenols. These metabolites influence various signaling pathways in epithelial cells, regulate the mucosal immune system in the host, and modulate gene expression of bacteria which results in the synthesis of enzymes associated with AA metabolism. This review aims to summarize the current literature relating to how the interactions between dietary amino acids and gut microbiota may promote host nutrition and health.

Circumventing the side effects of L-asparaginase

L-asparaginase is an enzyme that catalyzes the degradation of asparagine and successfully used in the treatment of acute lymphoblastic leukemia. L-asparaginase toxicity is either related to hypersensitivity to the foreign protein or to a secondary L-glutaminase activity that causes inhibition of protein synthesis. PEGylated versions have been incorporated into the treatment protocols to reduce immunogenicity and an alternative L-asparaginase derived from Dickeya chrysanthemi is used in patients with anaphylactic reactions to the E. coli L-asparaginase. Alternative approaches commonly explore new sources of the enzyme as well as the use of protein engineering techniques to create less immunogenic, more stable variants with lower L-glutaminase activity. This article reviews the main strategies used to overcome L-asparaginase shortcomings and introduces recent tools that can be used to create therapeutic enzymes with improved features.

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.

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.

Multi Gene Genetic Program Modelling on L-Asparaginase Activity of Bacillus Stratosphericus

The current study focuses on maximization of L-Asparaginase production from Bacillus stratosphericus isolated from Ocimum tenuiflorum. Optimization study followed by modelling using Artificial Neural Network (ANN) was performed. The experimental data obtained from Response Surface Methodology (RSM) was further studied by an evolutionary algorithm Genetic Programming (GP) to find the prediction equation. GP does not require prior knowledge of the data sets. GP is an extension of Genetic Algorithm (GA), where the results are represented in the form of trees. Multi gene genetic programming (MGPP) is a variant of GP used to solve non-linear mathematical models. The prediction equation obtained from the GP analysis is represented in the form of tree. Each tree represents single gene. Best fit individuals obtained at each generation by using genetic operators were selected to get better regression co-efficient value. The predicted and experimental data showed good significance with R2 = 0.99956.

An efficient expression tag library based on self-assembling amphipathic peptides

Background

Self-assembling amphipathic peptides (SAPs) may improve protein production or induce the formation of inclusion bodies by fusing them to the N-terminus of proteins. However, they do not function uniformly well with all target enzymes and systematic research on how the composition of SAPs influence the production of fusion protein is still limited.

Results

To improve the efficiency of SAPs, we studied factors that might be involved in SAP-mediated protein production using S1 (AEAEAKAK)₂ as the original SAP and green fluorescent protein (GFP) as the reporter. The results indicate that hydrophobicity and net charges of SAPs play a key role in protein expression. As hydrophobicity regulation tend to cause the formation of insoluble inclusion bodies of protein, an expression tag library composed of SAPs, which varied in net charge (from + 1 to + 20), was constructed based on the random amplification of S1nv1 (ANANARAR)₁₀. The efficiency of the library was validated by polygalacturonate lyase (PGL), lipoxygenase (LOX), l-asparaginase (ASN) and transglutaminase (MTG). To accelerate preliminary screening, each enzyme was fused at the C-terminus with GFP. Among the four enzyme fusions, the SAPs with + 2 – + 6 net charges were optimal for protein expression. Finally, application of the library improved the expression of PGL, LOX, ASN, and MTG by 8.3, 3.5, 2.64, and 3.68-fold relative to that of the corresponding wild-type enzyme, respectively.

Conclusions

This is the first report to study key factors of SAPs as an expression tag to enhance recombinant enzyme production. The SAP library could be used as a novel plug-and-play protein-engineering method to screen for enzymes or proteins with enhanced production.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1142-9) contains supplementary material, which is available to authorized users.

Expression, purification, and characterization of asparaginase II from Saccharomyces cerevisiae in Escherichia coli

l-asparaginase catalyzes the conversion of l-asparagine to l-aspartate and ammonium. This protein is an important therapeutic enzyme used for the treatment of acute lymphoblastic leukemia. In this study, the asparaginase II-encoding gene ASP3 from Saccharomyces cerevisiae was cloned into the expression vector pET28a in-fusion with a 6x histidine tag and was expressed in Escherichia coli BL21 (DE3) cells. The protein was expressed at a high level (225.6 IU/g cells) as an intracellular and soluble molecule and was purified from the supernatant by nickel affinity chromatography. The enzyme showed very low activity against l-glutamine. The denaturing electrophoresis analysis indicated that the recombinant protein had a molecular mass of ∼38 kDa. The native enzyme was a tetramer with a molecular mass of approximately 178 kDa. The enzyme preparation showed antitumor activity against the K562 and Jurkat cell lines comparable or even superior to the E. coli commercial asparaginase.

In silico characterization of a cyanobacterial plant-type isoaspartyl aminopeptidase/asparaginase

Asparaginases are found in a range of organisms, although those found in cyanobacteria have been little studied, in spite of their great potential for biotechnological application. This study therefore sought to characterize the molecular structure of an L-asparaginase from the cyanobacterium Limnothrix sp. CACIAM 69d, which was isolated from a freshwater Amazonian environment. After homology modeling, model validation was performed using a Ramachandran plot, VERIFY3D, and the RMSD. We also performed molecular docking and dynamics simulations based on binding free-energy analysis. Structural alignment revealed homology with the isoaspartyl peptidase/asparaginase (EcAIII) from Escherichia coli. When compared to the template, our model showed full conservation of the catalytic site. In silico simulations confirmed the interaction of cyanobacterial isoaspartyl peptidase/asparaginase with its substrate, β-Asp-Leu dipeptide. We also observed that the residues Thr154, Thr187, Gly207, Asp218, and Gly237 were fundamental to protein-ligand complexation. Overall, our results suggest that L-asparaginase from Limnothrix sp. CACIAM 669d has similar properties to E. coli EcAIII asparaginase. Our study opens up new perspectives for the biotechnological exploitation of cyanobacterial asparaginases.

Recent Progress in Micro/Nanoreactors toward the Creation of Artificial Organelles

Artificial organelles created from a bottom up approach are a new type of engineered materials, which are not designed to be living but, instead, to mimic some specific functions inside cells. By doing so, artificial organelles are expected to become a powerful tool in biomedicine. They can act as nanoreactors to convert a prodrug into a drug inside the cells or as carriers encapsulating therapeutic enzymes to replace malfunctioning organelles in pathological conditions. For the design of artificial organelles, several requirements need to be fulfilled: a compartmentalized structure that can encapsulate the synthetic machinery to perform an enzymatic function, as well as a means to allow for communication between the interior of the artificial organelle and the external environment, so that substrates and products can diffuse in and out the carrier allowing for continuous enzymatic reactions. The most recent and exciting advances in architectures that fulfill the aforementioned requirements are featured in this review. Artificial organelles are classified depending on their constituting materials, being lipid and polymer-based systems the most prominent ones. Finally, special emphasis will be put on the intracellular response of these newly emerging systems.

Salmonella FraE, an Asparaginase Homolog, Contributes to Fructose-Asparagine but Not Asparagine Utilization

Salmonella enterica can utilize fructose-asparagine (F-Asn) as a source of carbon and nitrogen. This capability has been attributed to five genes in the fra locus. Previously, we determined that mutations in fraB (deglycase), fraD (kinase), or fraA (transporter) eliminated the ability of Salmonella to grow on F-Asn, while a mutation in fraE allowed partial growth. We hypothesized that FraE, a putative periplasmic fructose-asparaginase, converts F-Asn to NH₄ ⁺ and fructose-aspartate (F-Asp). FraA could then transport F-Asp into the cytoplasm for subsequent catabolism. Here, we report that growth of the fraE mutant on F-Asn is caused by a partially redundant activity provided by AnsB, a periplasmic asparaginase. Indeed, a fraE ansB double mutant is unable to grow on F-Asn. Moreover, biochemical assays using periplasmic extracts of mutants that express only FraE or AnsB confirmed that each of these enzymes converts F-Asn to F-Asp and NH₄ ⁺ However, FraE does not contribute to growth on asparagine. We tested and confirmed the hypothesis that a fraE ansB mutant can grow on F-Asp, while mutants lacking fraA, fraD, or fraB cannot. This finding provides strong evidence that FraA transports F-Asp but not F-Asn from the periplasm to the cytoplasm. Previously, we determined that F-Asn is toxic to a fraB mutant due to the accumulation of the FraB substrate, 6-phosphofructose-aspartate (6-P-F-Asp). Here, we found that, as expected, a fraB mutant is also inhibited by F-Asp. Collectively, these findings contribute to a better understanding of F-Asn utilization by Salmonella IMPORTANCE Salmonella is able to utilize fructose-asparagine (F-Asn) as a nutrient. We recently reported that the disruption of a deglycase enzyme in the F-Asn utilization pathway inhibits the growth of Salmonella in mice and recognized this pathway as a novel and specific drug target. Here, we characterize the first step in the pathway wherein FraE hydrolyzes F-Asn to release NH₄ ⁺ and F-Asp in the periplasm of the cell. A fraE mutant continues to grow slowly on F-Asn due to asparaginase activity encoded by ansB.

Molecular dynamic simulations of Escherichia coli L-asparaginase to illuminate its role in deamination of asparagine and glutamine residues

Acute lymphocytic leukemia (ALL) is an outrageous disease worldwide. l-Asparagine (l-Asn) and l-Glutamine (l-Gln) deamination play a crucial role in ALL treatment. Role of Elspar^® (l-asparaginase from Escherichia coli) in regulation of l-Asn and l-Gln has been confirmed by the other researchers through experimental studies. Therapeutic research against ALL remained elusive with the lack of information on molecular interactions of Elspar^® with amino acid substrates. In the present study, using different docking tools binding cavities, key residues in binding and ligand binding mechanisms were identified. For the apo state enzyme and ligand bound state complexes, MD simulations were performed. Trajectory analysis for 30 ns run confirmed the kinship of l-Asn with l-asparaginase enzyme in the dynamic system with less stability in comparison to l-Gln docked complex. Overall findings strongly supported the bi-functional nature of the enzyme drug. A good number of conformational changes were observed with 1NNS structure due to ligand binding. Results of present study give much more information on structural and functional aspects of E. colil-asparaginase upon the interaction with its ligands which may be useful in designing effective therapeutics for ALL.

L-asparaginase as a critical component to combat Acute Lymphoblastic Leukaemia (ALL): A novel approach to target ALL

L-asparaginase, an anti-leukaemic drug that has been approved for clinical use for many years in the treatment of childhood Acute Lymphoblastic Leukaemia (ALL), is obtained from bacterial origin (Escherichia coli and Erwinia carotovora). The efficacy of L-asparaginase has been discussed for the past 40 years, and an ideal substitute for the enzyme has not yet been developed. The early clearance from plasma (short half-life) and requirement for multiple administrations and hence frequent physician visits make the overall treatment cost quite high. In addition, a high rate of allergic reactions in patients receiving treatment with the enzyme isolated from bacterial sources make its clinical application challenging. For these reasons, various attempts are being made to overcome these barriers. Therefore, the present article reviews studies focused on seeking substitutes for L-asparaginase through alternative sources including bacteria, fungi, actinomycetes, algae and plants to overcome these limitations. In addition, the role of chemical modifications and protein engineering approaches to enhance the drug's efficacy are also discussed. Moreover, an overview has also been provided in the current review regarding the contradiction among various researchers regarding the significance of the enzyme's glutaminase activity.

A critical review on properties and applications of microbial l-asparaginases

l-Asparaginase is one of the main drugs used in the treatment of acute lymphoblastic leukemia (ALL), a commonly diagnosed pediatric cancer. Although several microorganisms are found to produce l-asparaginase, only the purified enzymes from E. coli and Erwinia chrysanthemi are employed in the clinical and therapeutic applications in humans. However, their therapeutic response seldom occurs without some evidence of hypersensitivity and other toxic side effects. l-Asparaginase is also of prospective use in food industry to reduce the formation of acrylamide in fried, roasted or baked food products. This review is an attempt to compile information on the properties of l-asparaginases obtained from different microorganisms. The complications involved with the therapeutic use of the currently available l-asparaginases, and the enzyme's potential application as a food processing aid to mitigate acrylamide formation have also been reviewed. Further, avenues for searching alternate sources of l-asparaginase have been discussed, highlighting the prospects of endophytic microorganisms as a possible source of l-asparaginases with varied biochemical and pharmacological properties.

Structural and functional insights into an archaealL-asparaginase obtained through the linker-less assembly of constituent domains

Covalent linkers bridging the domains of multidomain proteins are considered to be crucial for assembly and function. In this report, an exception in which the linker of a two-domain dimeric L-asparaginase fromPyrococcus furiosus(PfA) was found to be dispensable is presented. Domains of this enzyme assembled without the linker into a conjoined tetrameric form that exhibited higher activity than the parent enzyme. The global shape and quaternary structure of the conjoined PfA were also similar to the wild-type PfA, as observed by their solution scattering profiles and X-ray crystallographic data. Comparison of the crystal structures of substrate-bound and unbound enzymes revealed an altogether new active-site composition and mechanism of action. Thus, conjoined PfA is presented as a unique enzyme obtained through noncovalent, linker-less assembly of constituent domains that is stable enough to function efficiently at elevated temperatures.

Haemostatic alterations induced by treatment with asparaginases and clinical consequences

The benefit of asparaginase for treating acute lymphoid leukaemia (ALL) has been well established. Native asparaginase derives from Escherichia coli (colaspase) or Erwinia chrysanthemi (crisantaspase); in a third preparation, colaspase is pegylated. Depletion of asparagine leads to decreased synthesis of procoagulant, anticoagulant, and fibrinolytic proteins, with resultant hypercoagulability and greater risk of venous thromboembolism (VTE). Colaspase and crisantaspase are not dose-equivalent, with crisantaspase displaying haemostatic toxicity only at dosages much higher and administered more frequently than those of colaspase. Cerebral venous thrombosis and pulmonary embolism are two life-endangering manifestations that occur during treatment with asparaginase particularly in children and in adults with ALL, respectively. Approximately one-third of VTEs are located in the upper extremities and are central venous line-related. Other risk factors are longer duration of asparaginase treatment and concomitant use of prednisone, anthracyclines, and oral contraceptives. The risk associated with inherited thrombophilia is uncertain but is clearly enhanced by other risk factors or by the use of prednisone. VTE prevention with fresh frozen plasma is not recommended; the efficacy of antithrombin (AT) concentrates has occasionally been reported, but these reports should be confirmed by proper studies, and AT should not be routinely employed. Therapeutic or prophylactic heparin doses are only partially effective, and direct thrombin or factor Xa inhibitors could play significant roles in the near future.

Cloning, expression, purification and characterisation of Erwinia carotovora L-asparaginase in Escherichia coli

Background:

For the past 30 years, bacterial L-asparaginases have been used as therapeutic agents in the treatment of acute childhood lymphoblastic leukemia. It is found in a variety of organisms such as microbes, plants and mammals. Their intrinsic low-rate glutaminase activity, however, causes serious side-effects, including neurotoxicity, hepatitis, coagulopathy and other dysfunctions. Erwinia carotovora asparaginase shows decreased glutaminase activity, so it is believed to have fewer side-effects in leukemia therapy. Our aim was to clone, express, purify and characterize E. carotovora asparaginase.

Materials and Methods:

L-asparaginase from E. carotovora NCYC 1526 (ErA) was cloned and expressed in Escherichia coli strain BL21 (DE3). The enzyme was purified to homogeneity by affinity chromatography. Various conditions were tested to maximize the production of recombinant asparaginase in E. coli.

Results:

A new L. asparaginase from E. carotovora NCYC 1526 (ErA) was successfully cloned, expressed and purified in E. coli BL21 (DE3). The specific activity of the enzyme was 430 IU/mg.

Conclusion:

The results of the present work form the basis for a new engineered form of ErA for future therapeutic use, which could be extended with crystallographic studies.

An Amplex Red-based fluorometric and spectrophotometric assay for L-asparaginase using its natural substrate

We report on the development of a sensitive real-time assay for monitoring the activity of L-asparaginase that hydrolyzes L-asparagine to L-aspartate and ammonia. In this method, L-aspartate is oxidized by L-aspartate oxidase to iminoaspartate and hydrogen peroxide (H2O2), and in the detection step horseradish peroxidase uses H2O2 to convert the colorless, nonfluorescent reagent Amplex Red to the red-colored and highly fluorescent product resorufin. The assay was validated in both the absorbance and the fluorescence modes. We show that, due to its high sensitivity and substrate selectivity, this assay can be used to measure enzymatic activity in human serum containing L-asparaginase.

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.

L-asparaginase: an effective agent in the treatment of acute lymphoblastic leukemia

L-asparaginase (L-ASNase) is an enzyme used most effectively in the treatment of acute lymphoblastic leukemia (ALL) for more than 30 years. It catalyzes the hydrolysis of amino acid l-asparagine to aspartic acid and ammonia, which leads to cell death. Clinical trials have been conducted using L-ASNase in combination with other drugs and radiotherapy, which have led to great success in the treatment of ALL. Treatments consist of induction therapy and central nervous system therapy. The achievement of complete remission in patients is associated with a few side-effects of using L-asparaginase, including pancreatitis, coagulation abnormalities and allergic reactions. Sometimes tumor cells may develop resistance to L-ASNase. To overcome these difficulties, the drug is modified by pegylation or immobilization, and also treatment protocols can be modified to increase the efficiency of the drug.

Recombinant intracellular Rhodospirillum rubrum L-asparaginase with low L-glutaminase activity and antiproliferative effect

The recombinant producer of Rhodospirillum rubrum L-asparaginase (RrA) was received and purification procedure of RrA was developed. It was shown that RrA has following biochemical and catalytic characteristics: K for L-asn 0,22 мM, pH optimum 9,2; temperature optimum 54°С; pI=5,1±0,3; L-gln activity seems to be low-to-negligible. К562, DU145 and MDA-MB-231 cellular lines displayed significant sensitivity towards the enzyme (IC50=1,80; 9,19 and 34,62 ME/ml, respectively. In comparison with L-asparaginases from E . coli II type (EcA) and Erwinia carotovora (EwA) cytotoxicity of RrA seems to be higher than EwA, but lower than EcA. 10-fold i.p. RrA administration (4000 ME/kg per day) in L5178y bearing mice showed Т/С=172%. The received results show that RrA belongs to I type cellular L-asparaginases with low L-gln activity and the high antiproliferative effect.

Rhizobium etli asparaginase II: an alternative for acute lymphoblastic leukemia (ALL) treatment

Bacterial l-asparaginase has been a universal component of therapies for childhood acute lymphoblastic leukemia since the 1970s. Two principal enzymes derived from Escherichia coli and Erwinia chrysanthemi are the only options clinically approved to date. We recently reported a study of recombinant l-asparaginase (AnsA) from Rhizobium etli and described an increasing type of AnsA family members. Sequence analysis revealed four conserved motifs with notable differences with respect to the conserved regions of amino acid sequences of type I and type II l-asparaginases, particularly in comparison with therapeutic enzymes from E. coli and E. chrysanthemi. These differences suggested a distinct immunological specificity. Here, we report an in silico analysis that revealed immunogenic determinants of AnsA. Also, we used an extensive approach to compare the crystal structures of E. coli and E. chrysantemi asparaginases with a computational model of AnsA and identified immunogenic epitopes. A three-dimensional model of AsnA revealed, as expected based on sequence dissimilarities, completely different folding and different immunogenic epitopes. This approach could be very useful in transcending the problem of immunogenicity in two major ways: by chemical modifications of epitopes to reduce drug immunogenicity, and by site-directed mutagenesis of amino acid residues to diminish immunogenicity without reduction of enzymatic activity.

Polyethylene Glycol-conjugated L-asparaginase versus native L-asparaginase in combination with standard agents for children with acute lymphoblastic leukemia in second bone marrow relapse: a Children's Oncology Group Study (POG 8866)

BACKGROUND

Administration of L-asparaginase is limited by hypersensitivity reactions mediated by anti-asparaginase antibodies. To overcome this problem, native Escherichia coli L-asparaginase was conjugated to polyethylene glycol (PEG) to formulate PEG-L-asparaginase, a preparation with decreased immunogenicity and increased circulating half-life. In early trials, PEG-L-asparaginase was tolerated by patients known to be hypersensitive to the native E. coli product.

METHODS

The Pediatric Oncology Group conducted a phase II, randomized trial to compare the efficacy and toxicity of PEG-L-asparaginase compared with native E. coli asparaginase in children with acute lymphoblastic leukemia in second bone marrow relapse. All patients (n=76) received standard doses of vincristine and prednisone. Nonhypersensitive patients (n=34) were randomized to receive either PEG-L-asparaginase of 2500 IU/m/dose intramuscularly on days 1 and 15 (treatment I) or native E. coli asparaginase of 10,000 IU/m/dose intramuscularly on days 1, 3, 5, 8, 10, 12, 15, 17, 19, 22, 24, and 26 (treatment II). Patients with a clinical history of an allergic reaction to unmodified asparaginase were directly assigned to treatment with PEG-L-asparaginase (n=42). Asparaginase levels and anti-asparaginase antibody titers were monitored in all patients. Response and toxicity were scored using conventional criteria.

RESULTS

The complete response rate for the total study population was 41%. There was no difference in complete response between patients randomized to PEG (47%) and native asparaginase (41%). PEG was well tolerated even in patients with prior allergic reactions to native asparaginase. PEG half-life was shorter in patients with prior allergy.

CONCLUSIONS

PEG asparaginase is a useful agent in patients with allergic reactions to native asparaginase.