Biochemical characterization of a novel L-asparaginase from Paenibacillus barengoltzii being suitable for acrylamide reduction in potato chips and mooncakes

Mitigation of acrylamide in fried food systems using a combination of zein-pectin hydrocolloid complex and a food-grade l-asparaginase

Acrylamide, a Maillard reaction product, formed in fried food poses a serious concern to food safety due to its neurotoxic and carcinogenic nature. A "Green Approach" using L-Asparaginase enzyme from GRAS-status bacteria synergized with hydrocolloid protective coating could be effective in inhibiting acrylamide formation. To fill this void, the present study reports a new variant of type-II L-asparaginase (AsnLb) from Levilactobacillus brevis NKN55, a food-grade bacterium isolated using a unique metabolite profiling approach. The recombinant AsnLb enzyme was characterized to study acrylamide inhibition ability and showed excellent specificity towards L-asparagine (157.2 U/mg) with Km, Vmax of 0.833 mM, 4.12 mM/min respectively. Pretreatment of potato slices with AsnLb (60 IU/mL) followed by zein-pectin nanocomplex led to >70% reduction of acrylamide formation suggesting synergistic effect of this dual component system. The developed strategy can be employed as a sustainable treatment method by food industries for alleviating acrylamide formation and associated health hazard in fried foods.

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.

Thermostable bacterial L-asparaginase for polyacrylamide inhibition and in silico mutational analysis

The L-asparaginase (ASPN) enzyme has received recognition in various applications including acrylamide degradation in the food industry. The synthesis and application of thermostable ASPN enzymes is required for its use in the food sector, where thermostable enzymes can withstand high temperatures. To achieve this goal, the bacterium Bacillus subtilis was isolated from the hot springs of Tapovan for screening the production of thermostable ASPN enzyme. Thus, ASPN with a maximal specific enzymatic activity of 0.896 U/mg and a molecular weight of 66 kDa was produced from the isolated bacteria. The kinetic study of the enzyme yielded a Km value of 1.579 mM and a Vmax of 5.009 µM/min with thermostability up to 100 min at 75 °C. This may have had a positive indication for employing the enzyme to stop polyacrylamide from being produced. The current study has also been extended to investigate the interaction of native and mutated ASPN enzymes with acrylamide. This concluded that the M10 (with 10 mutations) has the highest protein and thermal stability compared to the wild-type ASPN protein sequence. Therefore, in comparison to a normal ASPN and all other mutant ASPNs, M10 is the most favorable mutation. This research has also demonstrated the usage of ASPN in food industrial applications.

Evaluation of the efficiency of thermostable L-asparaginase from B. licheniformis UDS-5 for acrylamide mitigation during preparation of French fries

A thermostable L-asparaginase was produced from Bacillus licheniformis UDS-5 (GenBank accession number, OP117154). The production conditions were optimized by the Plackett Burman method, followed by the Box Behnken method, where the enzyme production was enhanced up to fourfold. It secreted L-asparaginase optimally in the medium, pH 7, containing 0.5% (w/v) peptone, 1% (w/v) sodium chloride, 0.15% (w/v) beef extract, 0.15% (w/v) yeast extract, 3% (w/v) L-asparagine at 50 °C for 96 h. The enzyme, with a molecular weight of 85 kDa, was purified by ion exchange chromatography and size exclusion chromatography with better purification fold and percent yield. It displayed optimal catalysis at 70 °C in 20 mM Tris-Cl buffer, pH 8. The purified enzyme also exhibited significant salt tolerance too, making it a suitable candidate for the food application. The L-asparaginase was employed at different doses to evaluate its ability to mitigate acrylamide, while preparing French fries without any prior treatment. The salient attributes of B. licheniformis UDS-5 L-asparaginase, such as greater thermal stability, salt stability and acrylamide reduction in starchy foods, highlights its possible application in the food industry.

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.

Effective mitigation in the amount of acrylamide through enzymatic approaches

Acrylamide (AA), as a food-borne toxicant, is created at some stages of thermal processing in the starchy food through Maillard reaction, fatty food via acrolein route, and proteinous food using free amino acids pathway. Maillard reaction obviously takes place in thermal-based products, being responsible for specific sensory attributes; AA formation, thereby, is unavoidable during the thermal processing. Additionally, AA can naturally occur in soil and water supply. In order to reduce the levels of acrylamide in cooked foods, mitigation techniques can be separated into three different types. Firstly, starting materials low in acrylamide precursors can be used to reduce the acrylamide in the final product. Secondly, process conditions may be modified in order to decrease the amount of acrylamide formation. Thirdly, post-process intervention could be used to reduce acrylamide. Conventional or emerging mitigation techniques might negatively influence the pleasant features of heated foods. The current study summarizes the effect of enzymatic reaction induced by asparaginase, glucose oxidase, acrylamidase, phytase, amylase, and protease to possibly inhibit AA formation or progressively hydrolyze formed AA. Not only enzyme-assisted AA reduction could dramatically maintain bio-active compounds, but also no damaging impact has been reported on the sensorial and rheological properties of the final heated products. The enzyme engineering can be applied to ameliorate enzyme functionality through altering the amino acid sequence like site-specific mutagenesis and directed evolution, chemical modifications by covalent conjugation of L-asparaginase onto soluble/insoluble biocompatible polymers and immobilization. Moreover, it would be possible to improve the enzyme's physical, chemical, and thermal stability, recyclability and prevent enzyme overuse by applying engineered ones. In spite of enzymes' cost-effective and eco-friendly, promoting their large-scale usages for AA reduction in food application and AA bioremediation in wastewater and soil resources.

Characterization of L-asparaginase from Streptomyces koyangensis SK4 with acrylamide-minimizing potential in potato chips

Microbial L-asparaginase is well known for its application in food industries to reduce acrylamide content in fried starchy food. L-asparaginase produced by Arctic actinomycetes Streptomyces koyangensis SK4 was purified and studied for biochemical characterization. The L-asparaginase was purified with a yield of 15.49% and final specific activity of 179.77 IU/mg of protein. The enzyme exhibited a molecular weight of 43 kDa. The optimum pH and temperature for maximum activity of the purified enzyme were 8.5 °C and 40 °C, respectively. The enzyme expressed maximum activity at an incubation period of 30 min and a substrate concentration of 0.06 M. The enzyme has a low Km value of 0.041 M and excellent substrate specificity toward L-asparagine. The enzyme activity was inhibited by metal ions Ba2+ and Hg2+, while Mn2+ and Mg2+ enhanced the activity. The study evaluated the acrylamide reduction potential of L-asparaginase from Streptomyces koyangensis SK4 in potato chips. The blanching plus L-asparaginase treatment of potato slices resulted in a 50% reduction in acrylamide content. The study illustrated an effective acrylamide reduction strategy in potato chips using L-asparaginase from a psychrophilic actinomycete. Besides the acrylamide reduction potential, L-asparaginase from Streptomyces koyangensis SK4 also did not exhibit any glutaminase or urease activity which is an outstanding feature of L-asparaginase to be used as a chemotherapeutic agent.

Production and optimization of l-asparaginase by Streptomyces koyangensis SK4 isolated from Arctic sediment

Actinomycetes isolated from the Arctic sediment were evaluated for the production of the enzyme l-asparaginase, an enzyme used to treat acute lymphoblastic leukemia. The most potent strain Streptomyces koyangensis SK4 was selected for l-asparaginase enzyme production by submerged fermentation. The effect of various fermentation parameters on enzyme production was analyzed statistically using the Plackett-Burman design and response surface method. Effects of eight parameters including temperature, pH, incubation time, inoculum size, agitation speed, the concentration of starch, l-asparagine, and yeast extract were studied on l-asparaginase production by the Arctic isolate S. koyangensis SK4. Factors such as temperature, pH, incubation time, agitation speed, and l-asparagine concentration were found to be important factors influencing  l-asparaginase production. Maximum enzyme activity of 136 IU/ml was obtained at 20°C on the seventh day of incubation in the asparagine dextrose broth maintained at pH 7.5, agitation speed 125 rpm, and l-asparagine concentration of 7.5 g/L. The statistical optimization method described in this study proved effective for increasing the l-asparaginase production by Arctic actinomycetes.

Marine enzymes: Classification and application in various industries

Oceans are regarded as a plentiful and sustainable source of biological compounds. Enzymes are a group of marine biomaterials that have recently drawn more attention because they are produced in harsh environmental conditions such as high salinity, extensive pH, a wide temperature range, and high pressure. Hence, marine-derived enzymes are capable of exhibiting remarkable properties due to their unique composition. In this review, we overviewed and discussed characteristics of marine enzymes as well as the sources of marine enzymes, ranging from primitive organisms to vertebrates, and presented the importance, advantages, and challenges of using marine enzymes with a summary of their applications in a variety of industries. Current biotechnological advancements need the study of novel marine enzymes that could be applied in a variety of ways. Resources of marine enzyme can benefit greatly for biotechnological applications duo to their biocompatible, ecofriendly and high effectiveness. It is beneficial to use the unique characteristics offered by marine enzymes to either develop new processes and products or improve existing ones. As a result, marine-derived enzymes have promising potential and are an excellent candidate for a variety of biotechnology applications and a future rise in the use of marine enzymes is to be anticipated.

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.

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.

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 Characterization of a Stable and Robust L-Asparaginase from Pseudomonas sp. PCH199: Evaluation of Cytotoxicity and Acrylamide Mitigation Potential

L-asparaginase is an important industrial enzyme widely used to treat acute lymphoblastic leukemia (ALL) and to reduce acrylamide formation in food products. In the current study, a stable and robust L-asparaginase from Pseudomonas sp. PCH199, with a high affinity for L-asparagine, was cloned and expressed in Escherichia coli BL21(DE3). Recombinant L-asparaginase (Pg-ASNase II) was purified with a monomer size of 37.0 kDa and a native size of 148.0 kDa. During characterization, Pg-ASNase II exhibited 75.8 ± 3.84 U/mg specific activities in 50.0 mM Tris-HCl buffer (pH 8.5) at 50 °C. However, it retained 80 and 70% enzyme activity at 37 °C and 50 °C after 60 min, respectively. The half-life and kd values were 625.15 min and 1.10 × 10−3 min−1 at 37 °C. The kinetic constant Km, Vmax, kcat, and kcat/Km values were 0.57 mM, 71.42 U/mg, 43.34 s−1, and 77.90 ± 9.81 s−1 mM−1 for L-asparagine, respectively. In addition, the enzyme has shown stability in the presence of most metal ions and protein-modifying agents. Pg-ASNase II was cytotoxic towards the MCF-7 cell line (breast cancer) with an estimated IC50 value of 0.169 U/mL in 24 h. Further, Pg-ASNase II treatment led to a 70% acrylamide reduction in baked foods. These findings suggest the potential of Pg-ASNase II in therapeutics and the food industry.

The role of additives on acrylamide formation in food products: a systematic review

Acrylamide (AA) is a toxic substance formed in many carbohydrate-rich food products, whose formation can be reduced by adding some additives. Furthermore, the type of food consumed determines the AA intake. According to the compiled information, the first route causing AA formation is the Maillard reaction. Some interventions, such as reducing AA precursors in raw materials, (i.e., asparagine), reducing sugars, or decreasing temperature and processing time can be applied to limit AA formation in food products. The L-asparaginase is more widely used in potato products. Also, coatings loaded with proteins, enzymes, and phenolic compounds are new techniques for reducing AA content. Enzymes have a reducing effect on AA formation by acting on asparagine; proteins by competing with amino acids to participate in Maillard, and phenolic compounds through their radical scavenging activity. On the other hand, some synthetic and natural additives increase the formation of AA. Due to the high exposure to AA and its toxic effects, it is essential to recognize suitable food additives to reduce the health risks for consumers. In this sense, this study focuses on different additives that are proven to be effective in the reduction or formation of AA in food products.

Characterization of a novel and glutaminase-free type II L-asparaginase from Corynebacterium glutamicum and its acrylamide alleviation efficiency in potato chips

Type II L-asparaginase as a pivotal enzyme agent has been applied to treating for acute lymphoblastic leukemia (ALL) and efficient mitigation of acrylamide formed in fried and baked foods. However, low activity, narrow range of pH stability, as well as undesirable glutaminase activity hinder the applications of this enzyme. In our work, A novel type II L-asparaginase (CgASNase) from Corynebacterium glutamicum with molecular mass of about 35 kDa was chosen to express in E. coli. CgASNase shared only 27 % structural identity with the reported L-asparaginase from Helicobacter pylori. The purified CgASNase showed the highest specific activity of 1979.08 IU mg^-1 to L-asparagine, compared with reported type II ASNases in the literature. CgASNase displayed superior stability at a wide pH range from 5.0 to 11.0, and retained about 76 % of its activity at 30 °C for 30 min. The kinetic parameters K_m (Michaelis constant), k_cat (turnover number), and k_cat/K_m (catalytic efficiency) values of 4.66 mM, 79,697.40 min^-1, and 17,102.45 mM^-1 min^-1, respectively. More importantly, CgASNase exhibited strict substrate specificity towards L-asparagine, no detectable activity to l-glutamine. To explore its ability to catalyze L-asparagine, CgASNase was supplied in frying potato chips, which produced the fries with 84 % less acrylamide content compared with no supply. These findings suggest that CgASNase presents excellent properties for chemotherapy against diseases and great potential in the food processing industry.

Biochemical characterization and detection of antitumor activity of l-asparaginase from thermophilic Geobacillus kaustophilus DSM 7263T

L-asparaginases, which are oncolytic enzymes, have been used in clinical applications for many years. These enzymes are also important in food processing industry due to their potential in acrylamide-mitigation. In this study, the gene for l-asparaginase (GkASN) from a thermophilic bacterium, Geobacillus kaustophilus, was cloned and expressed in E. coli Rosetta™2 (DE3) cells utilizing the pET-22b(+) vector. The 6xHis-tag attached enzyme was purified and analyzed both biochemically and structurally. The molecular mass of GkASN was determined as ∼36 kDa by SDS-PAGE, Western Blotting, and MALDI-TOF MS analyses. Optimum temperature and pH for the enzyme was determined as 55 °C and 8.5, respectively. The enzyme retained 89% of its thermal stability at 37 °C and 75% at 55 °C after 6 h of incubation. The enzyme activity was inhibited in the presence of Cu²⁺, Fe³⁺, Zn²⁺, and EDTA, while the activity was enhanced in the presence of Mn²⁺, Mg²⁺, and thiol group protective agents such as 2-mercaptoethanol and DTT. The structural modeling analysis demonstrated that the catalytic residues of the enzyme were partially similar to other asparaginases. The therapeutic potential of GkASN was tested on hepatocellular carcinoma cells, a solid cancer type with high mortality rate and rapidly increasing incidence in recent years. We showed that the GkASN-induced asparagine deficiency effectively reduced the metastatic synergy in HCC SNU387 cells on a xCELLigence system with differentiated epithelial Hep3B and poorly differentiated metastatic mesenchymal HCC SNU387 cells.

A systematic review of recent trends in research on therapeutically significant L-asparaginase and acute lymphoblastic leukemia

L-asparaginases are mostly obtained from bacterial sources for their application in the therapy and food industry. Bacterial L-asparaginases are employed in the treatment of Acute Lymphoblastic Leukemia (ALL) and its subtypes, a type of blood and bone marrow cancer that results in the overproduction of immature blood cells. It also plays a role in the food industry in reducing the acrylamide formed during baking, roasting, and frying starchy foods. This importance of the enzyme makes it to be of constant interest to the researchers to isolate novel sources. Presently L-asparaginases from E. coli native and PEGylated form, Dickeya chrysanthemi (Erwinia chrysanthemi) are in the treatment regime. In therapy, the intrinsic glutaminase activity of the enzyme is a major drawback as the patients in treatment experience side effects like fever, skin rashes, anaphylaxis, pancreatitis, steatosis in the liver, and many complications. Its significance in the food industry in mitigating acrylamide is also a major reason. Acrylamide, a potent carcinogen was formed when treating starchy foods at higher temperatures. Acrylamide content in food was analyzed and pre-treatment was considered a valuable option. Immobilization of the enzyme is an advancing and promising technique in the effective delivery of the enzyme than in free form. The concept of machine learning by employing the Artificial Network and Genetic Algorithm has paved the way to optimize the production of L-asparaginase from its sources. Gene-editing tools are gaining momentum in the study of several diseases and this review focuses on the CRISPR-Cas9 gene-editing tool in ALL.

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 molecular insights on the bioactivity and binding interactions of Bacillus australimaris NJB19 L-asparaginase

L-asparaginase, an antileukemic enzyme, is indispensable to the treatment of Acute Lymphoblastic Leukemia (ALL). However, the intrinsic glutaminase activity entails various side effects to the patients; thus, an improved version of the enzyme lacking glutaminase activity would be a requisite for effective treatment management of ALL. The present study highlights the biochemical and molecular characteristics of the recombinant glutaminase-free L-asparaginase from Bacillus australimaris NJB19 (BaAsp). Investigation of the active site architecture of the protein unraveled the binding interactions of BaAsp with its substrate. Comparative analysis of the L-asparaginase sequences revealed few substitutions of key amino acids in the BaAsp that could construe its substrate selectivity and specificity. The purified heterologously expressed protein (42 kDa) displayed maximum L-asparaginase activity at 35-40 °C and pH 8.5-9, with no observed L-glutaminase activity. The kinetic parameters, Km and Vmax, were determined as 45.6 μM and 0.16 μmoles min^-1, respectively. Furthermore, in silico analysis revealed a conserved zinc-binding site in the protein, which is generally implicated in inhibiting the L-asparaginase activity. However, BaAsp was not inhibited by zinc at 1 mM concentration. Therefore, the findings provide insights on the biochemical and molecular details of BaAsp, which could be valuable in formulating it for alternate antileukemic drug therapy.

Production of a Novel Marine Pseudomonas aeruginosa Recombinant L-Asparaginase: Insight on the Structure and Biochemical Characterization

The present study focused on the cloning, expression, and characterization of L-asparaginase of marine Pseudomonas aeruginosa HR03 isolated from fish intestine. Thus, a gene fragment containing the L-asparaginase sequence of Pseudomonas aeruginosa HR03 isolated from the fish intestine was cloned in the pET21a vector and then expressed in Escherichia coli BL21 (DE3) cells. Thereafter, the recombinant L-asparaginase (HR03Asnase) was purified by nickel affinity chromatography, and the enzymatic properties of HR03Asnase, including the effects of pH and temperature on HR03Asnase activity and its kinetic parameters, were determined. The recombinant enzyme HR03Asnase showed the highest similarity to type I L-asparaginase from Pseudomonas aeruginosa. The three-dimensional (3D) modeling results indicate that HR03Asnase exists as a homotetramer. Its molecular weight was 35 kDa, and the maximum activity of the purified enzyme was observed at pH8 and at 40 °C. The k_m and V_max of the enzyme obtained with L-asparagine as substrate were 10.904 mM and 3.44 × 10^-2 mM/min, respectively. The maximum activity of HR03Asnase was reduced by 50% at 90 °C after 10-min incubation; however, the enzyme maintained more than 20% of its activity after 30-min incubation. This enzyme also maintained almost 50% of its activity at pH 12 after 40-min incubation. The evaluation of pH and temperature stability of HR03Asnase showed that the enzyme has a wide range of activity, which is a suitable characteristic for its application in different industries. Overall, the results of the present study indicate that marine sources are promising biological reservoirs for enzymes to be used for biotechnological purposes, and marine thermostable HR03Asnase is likely a potential candidate for its future usage in the pharmaceutical and food industries.

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.

Construction of L-Asparaginase Stable Mutation for the Application in Food Acrylamide Mitigation

Acrylamide, a II A carcinogen, widely exists in fried and baked foods. L-asparaginase can inhibit acrylamide formation in foods, and enzymatic stability is the key to its application. In this study, the Escherichia coli L-asparaginase (ECA) stable variant, D60W/L211R/L310R, was obtained with molecular dynamics (MD) simulation, saturation mutation, and combinatorial mutation, the half-life of which increased to 110 min from 60 min at 50 °C. Furthermore, the working temperature (maintaining the activity above 80%) of mutation expanded from 31 °C–43 °C to 35 °C–55 °C, and the relative activity of mutation increased to 82% from 65% at a pH range of 6–10. On treating 60 U/mL and 100 U/g flour L-asparaginase stable mutant (D60W/L211R/L310R) under uncontrolled temperature and pH, the acrylamide content of potato chips and bread was reduced by 66.9% and 51.7%, which was 27% and 49.9% higher than that of the wild type, respectively. These results demonstrated that the mutation could be of great potential to reduce food acrylamide formation in practical applications.

Characterization of a Novel L-Asparaginase from Mycobacterium gordonae with Acrylamide Mitigation Potential

L-asparaginase (E.C.3.5.1.1) is a well-known agent that prevents the formation of acrylamide both in the food industry and against childhood acute lymphoblastic leukemia in clinical settings. The disadvantages of L-asparaginase, which restrict its industrial application, include its narrow range of pH stability and low thermostability. In this study, a novel L-asparaginase from Mycobacterium gordonae (GmASNase) was cloned and expressed in Escherichia coli BL21 (DE3). GmASNase was found to be a tetramer with a monomeric size of 32 kDa, sharing only 32% structural identity with Helicobacter pylori L-asparaginases in the Protein Data Bank database. The purified GmASNase had the highest specific activity of 486.65 IU mg⁻¹ at pH 9.0 and 50 °C. In addition, GmASNase possessed superior properties in terms of stability at a wide pH range of 5.0–11.0 and activity at temperatures below 40 °C. Moreover, GmASNase displayed high substrate specificity towards L-asparagine with Km, kcat, and kcat/Km values of 6.025 mM, 11,864.71 min⁻¹ and 1969.25 mM⁻¹min⁻¹, respectively. To evaluate its ability to mitigate acrylamide, GmASNase was used to treat potato chips prior to frying, where the acrylamide content decreased by 65.09% compared with the untreated control. These results suggest that GmASNase is a potential candidate for applications in the food industry.

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.

Microbial production, molecular modification, and practical application of l-Asparaginase: A review

L-Asparaginase (L-ASNase, EC 3.5.1.1), an antitumor drug for acute lymphoblastic leukemia (ALL) therapy, is widely used in the clinical field. Similarly, L-ASNase is also a powerful and significant biological tool in the food industry to inhibit acrylamide (AA) formation. This review comprehensively summarizes the latest achievements and improvements in the production, modification, and application of microbial L-ASNase. To date, the expression levels and optimization of expression hosts such as Escherichia coli, Bacillus subtilis, and Pichia pastoris, have made significant progress. In addition, examples of successful modification of L-ASNase such as decreasing glutaminase activity, increasing the in vivo stability, and enhancing thermostability have been presented. Impressively, the application of L-ASNase as a food addition aid, as well as its commercialization in the pharmaceutical field, and cutting-edge biosensor application developments have been summarized. The presented results and proposed ideas could be a good guide for other L-ASNase researchers in both scientific and practical fields.

L-asparaginase production review: bioprocess design and biochemical characteristics

In the past decades, the production of biopharmaceuticals has gained high interest due to its great sensitivity, specificity, and lower risk of negative effects to patients. Biopharmaceuticals are mostly therapeutic recombinant proteins produced through biotechnological processes. In this context, L-asparaginase (L-asparagine amidohydrolase, L-ASNase (E.C. 3.5.1.1)) is a therapeutic enzyme that has been abundantly studied by researchers due to its antineoplastic properties. As a biopharmaceutical, L-ASNase has been used in the treatment of acute lymphoblastic leukemia (ALL), acute myeloblastic leukemia (AML), and other lymphoid malignancies, in combination with other drugs. Besides its application as a biopharmaceutical, this enzyme is widely used in food processing industries as an acrylamide mitigation agent and as a biosensor for the detection of L-asparagine in physiological fluids at nano-levels. The great demand for L-ASNase is supplied by recombinant enzymes from Escherichia coli and Erwinia chrysanthemi. However, production processes are associated to low yields and proteins associated to immunogenicity problems, which leads to the search for a better enzyme source. Considering the L-ASNase pharmacological and food importance, this review provides an overview of the current biotechnological developments in L-ASNase production and biochemical characterization aiming to improve the knowledge about its production. KEY POINTS: • Microbial enzyme applications as biopharmaceutical and in food industry • Biosynthesis process: from the microorganism to bioreactor technology • Enzyme activity and kinetic properties: crucial for the final 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.

Characterization of Penicillium crustosum L-asparaginase and its acrylamide alleviation efficiency in roasted coffee beans at non-cytotoxic levels

This work aims at isolating a fungal source for L-asparaginase production to be applied in reducing acrylamide levels in coffee beans at non-cytotoxic levels. An L-asparaginase-producing fungus was isolated from an agricultural soil sample and identified as Penicillium crustosum NMKA 511. A maximum L-asparaginase activity of 19.10 U/mL was obtained by the above-mentioned fungus when grown under optimum conditions (i.e. 16.96 g/L sucrose as carbon source, 1.92 g/L peptone as nitrogen source, pH 7.7 and 33.5 °C). Further, the produced L-asparaginase was purified and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that P. crustosum L-asparaginase was a heterodimer enzyme with molecular weights of approximately 41.3 and 44.4 kDa. Also, the purified P. crustosum L-asparaginase was specific towards L-asparagine and showed negligible and no effects towards L-glutamine and D-asparagine, respectively. Additionally, the purified L-asparaginase reduced the acrylamide levels by 80.7% and 75.8% in light and dark roasted coffee beans, respectively. The amount of L-asparaginase used to reduce acrylamide was considered safe when cell viability reached 94.6%.

A potential type-II L-asparaginase from marine isolate Bacillus australimaris NJB19: Statistical optimization, in silico analysis and structural modeling

L-asparaginase is a cardinal biotherapeutic drug for treating acute lymphoblastic leukemia, which is highly prevalent in children worldwide. In the current investigation, L-asparaginase producing marine bacterial isolate, Bacillus australimaris NJB19 (MG734654), was observed to be producing extracellular glutaminase free L-asparaginase (13.27 ± 0.4 IU mL^-1). Production of L-asparaginase was enhanced by the Box-Behnken design approach that enumerated the significant variables affecting the enzyme production. The optimum levels of the derived variables resulted in 2.8-fold higher levels of the enzyme production (37.93 ± 1.06 IU mL^-1). An 1146 bp L-asparaginase biosynthetic gene of Bacillus australimaris NJB19 was identified and cloned in E. coli DH5α, fused with a histidine tag. The in silico analysis of the protein sequence revealed the presence of a signal peptide and classified it as a type II L-asparaginase. Toxic peptide prediction disclosed no toxin domain in the protein sequence, hence suggesting it as a non-toxic protein. The secondary structure analysis of the enzyme displayed a comparable percentage of alpha-helical and random coil structure, while 14.39% and 6.57% of amino acid residues were composed of extended strands and beta-turns, respectively. The functional sites in the three-dimensional structural model of the protein were predicted and interestingly had a few less conserved residues. Bacillus australimaris NJB19 identified in this study produces type-II L-asparaginase, known for its high affinity for asparagine and effectiveness against leukemic cells. Hence, these observations indicate the L-asparaginase, thus obtained, as a potentially significant and novel therapeutic drug.

Pseudomonas aeruginosa recombinant L-asparaginase: Large scale production, purification, and cytotoxicity on THP-1, MDA-MB-231, A549, Caco2 and HCT-116 cell lines

In previous studies Pseudomonas aeruginosal-ASNase complete coding sequence gene, 984 bp (GenBank accession number KU161101.2) was isolated by PCR, cloned into pET28a(+) vector, expressed in E. coli DE3(BL21) pLysS, purified to apparent homogeneity and biochemically characterized. In the present work we highlight large scale production, affinity purification of the recombinant enzyme, effect of osmolytes on the stability of the l-ASNase and cytotoxicity on different cancer cell lines. Successful overexpression was achieved in E. coli as a 6-His-Tag fusion protein after 18 h of induction with lactose at a concentration of 2 g/L in fermentation medium and at 37 °C. The recombinant enzyme was purified to homogeneity using Ni²⁺ chelated Fast Flow Sepharose resin with 19758.8 specific activity and 10.28 purification fold. With respect to the effect of osmolytes on the stability of the purified enzyme, the majority of the tested osmolytes namely 5% maltose, 5% mannitol, 30% glycerol and 5% BSA were found to increase the stability of the recombinant l-ASNase as compared to the free enzyme. Triple negative breast cancer cell line, MDA-MB-231 treated with recombinant l-ASNase showed significant morphological changes and the IC₅₀ of the purified enzyme was found to be 3.1 IU. Human leukemia cell line, THP-1 treated with l-ASNase showed apoptotic bodies and morphological changes with IC₅₀ of the purified enzyme 1.75 IU. Moreover, the purified recombinant l-ASNase was found to induced cytotoxic effects on colorectal adenocarcinoma cell line, Caco-2 with IC₅₀ of 68.28 IU. Results of apoptosis assay on THP-1 cells revealed that the purified l-ASNase induced early and late apoptosis at 14.16% and 7.56 respectively as compared to the control untreated cells.

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.

Purification and biotechnological applications of L-asparaginase from newly isolated Bacillus halotolerans OHEM18 as antitumor and antioxidant agent

In the present study, a new bacterial strain, Bacillus halotolerans OHEM18 was significantly found to produce extracellular L-asparaginase. L-asparaginase was purified using ammonium sulfate precipitation and QFF column to 3.84-fold with specific activity of 215.33 U/mg and its molecular mass was assessed to be 41.5 kDa. Maximum enzyme activity was determined at pH 8.2 and 40 °C and with retaining 70% of its activity after incubation for 1 h at 50 °C. Km and Vmax values were determined to be 0.0047 M and 92.74, respectively. Cytotoxicity test indicated a significant safety of L-asparaginase on Vero cells with selectivity against leukemia, breast cancer and hepatoma cells. NFS-60 cells was the most sensitive tumor cells to L-asparaginase with IC₅₀ of 10.29 µg/ml and selectivity index of 30.61. This selectivity was recognized to be an apoptosis-dependent mechanism proven via cell cycle arrest in sub-G1 phase and fragmentation of genomic DNA. L-asparaginase showed antioxidant activity against both DPPH and ABTS radicals with IC₅₀ values of 64.07 and 177.1 mg/ml, respectively. These competitive advantage of bacterial L-asparaginase over than other sources is that it might be produced in large amounts through production in large-scale biofermenters, which decreases costs, besides having a sustainable bacterial source. Our findings established that the potent cytotoxic effect of L-asparaginase isolated from B. halotolerans OHEM18 may be a promise candidate for further medicinal applications as an antioxidant and antitumor drug.Communicated by Ramaswamy H. Sarma.

Spirulina maxima L-asparaginase: Immobilization, Antiviral and Antiproliferation Activities

BACKGROUND

L-asparaginase (L-AsnA) enzyme has gained significant attention in the food, biocatalysts and pharmaceutics industry. It (L-AsnA) has been widely used in food processing industries as a promising acrylamide mitigating agent and as a therapeutic agent in the treatment of certain human cancers.

OBJECTIVE

Based on US Patent (4,433,054; 1984), L-asparaginase (L-AsnA) enzyme is immobilized by admixing the active enzyme on the polysaccharide to be in a gel form. The storage stability of immobilized L-AsnA enzyme and its anti-proliferation and antiviral activity were determined.

METHODS

In the present study, S. maxima was cultured at large scales (300 liter) for the production of enough extracellular L-asparaginase (L-AsnA) using modified (high N concentration) Zarrouk medium as we reported in a previous study. L-AsnA was immobilized on natural polymers, as agar cake beads, agarose pieces and gelatin blocks, in order to evaluate the efficiency of physical entrapment techniques. Anti-proliferation properties of L-AsnA against lung carcinoma A549, hepatocellular carcinoma Hep-G2 and prostate carcinoma PC3 human cancer cell lines were assessed by the MTT cell viability method. In addition, the antiviral activity against Coxsackie B3 (CSB3) Virus was assessed.

RESULTS

The highest L-AsnA immobilized activity and immobilization yield were achieved with agar cakes bead. The purified S. maxima L-AsnA showed good antiviral activity against Coxsackie B3 (CSB3) Virus in a dose-dependent manner with an IC50 value 17.03 μg/ml. The antiviral mode of action is presumably due to their capability of inhibiting attachment, blocking the adsorption and penetration event of the viral replication cycle with 89.24%, 72.78% and 72.78%, respectively. Also, S. maxima L-AsnA showed anti-proliferation effect against lung carcinoma A549, hepatocellular carcinoma Hep-G2 and prostate carcinoma PC3 human cancer cell lines, with an IC50 of 22.54, 24.65 and 56.61 μg/ml, respectively.

CONCLUSION

It is interesting to favor L-asparaginase of S. maxima which showed antiviral activity and anti-proliferation effect against different types of human cell lines. Thus, S. maxima microalgae might be a good source for L-AsnA enzymes and can be immobilized on natural polymers.

Simultaneous cell disruption and semi-quantitative activity assays for high-throughput screening of thermostable L-asparaginases

L-asparaginase, which catalyses the hydrolysis of L-asparagine to L-aspartate, has attracted the attention of researchers due to its expanded applications in medicine and the food industry. In this study, a novel thermostable L-asparaginase from Pyrococcus yayanosii CH1 was cloned and over-expressed in Bacillus subtilis 168. To obtain thermostable L-asparaginase mutants with higher activity, a robust high-throughput screening process was developed specifically for thermophilic enzymes. In this process, cell disruption and enzyme activity assays are simultaneously performed in 96-deep well plates. By combining error-prone PCR and screening, six brilliant positive variants and four key amino acid residue mutations were identified. Combined mutation of the four residues showed relatively high specific activity (3108 U/mg) that was 2.1 times greater than that of the wild-type enzyme. Fermentation with the mutant strain in a 5-L fermenter yielded L-asparaginase activity of 2168 U/mL.

Marine microbial L-asparaginase: Biochemistry, molecular approaches and applications in tumor therapy and in food industry

The marine environment is a rich source of biological and chemical diversity. It covers more than 70% of the Earth's surface and features a wide diversity of habitats, often displaying extreme conditions, where marine organisms thrive, offering a vast pool for microorganisms and enzymes. Given the dissimilarity between marine and terrestrial habitats, enzymes and microorganisms, either novel or with different and appealing features as compared to terrestrial counterparts, may be identified and isolated. L-asparaginase (E.C. 3.5.1.1), is among the relevant enzymes that can be obtained from marine sources. This amidohydrolase acts on L-asparagine and produce L-aspartate and ammonia, accordingly it has an acknowledged chemotherapeutic application, namely in acute lymphoblastic leukemia. Moreover, L-asparaginase is also of interest in the food industry as it prevents acrylamide formation. Terrestrial organisms have been largely tapped for L-asparaginases, but most failed to comply with criteria for practical applications, whereas marine sources have only been marginally screened. This work provides an overview on the relevant features of this enzyme and the framework for its application, with a clear emphasis on the use of L-asparaginase from marine sources. The review envisages to highlight the unique properties of marine L-asparaginases that could make them good candidates for medical applications and industries, especially in food safety.