Expression in Escherichia coli of a gene encoding type II l-asparaginase from Bacillus subtilis, and characterization of its unique properties

Characterization of a Type II L-Asparaginase from the Halotolerant Bacillus subtilis CH11

L-asparaginases from bacterial sources have been used in antineoplastic treatments and the food industry. A type II L-asparaginase encoded by the N-truncated gene ansZP21 of halotolerant Bacillus subtilis CH11 isolated from Chilca salterns in Peru was expressed using a heterologous system in Escherichia coli BL21 (DE3)pLysS. The recombinant protein was purified using one-step nickel affinity chromatography and exhibited an activity of 234.38 U mg-1 and a maximum catalytic activity at pH 9.0 and 60 °C. The enzyme showed a homotetrameric form with an estimated molecular weight of 155 kDa through gel filtration chromatography. The enzyme half-life at 60 °C was 3 h 48 min, and L-asparaginase retained 50% of its initial activity for 24 h at 37 °C. The activity was considerably enhanced by KCl, CaCl2, MgCl2, mercaptoethanol, and DL-dithiothreitol (p-value < 0.01). Moreover, the Vmax and Km were 145.2 µmol mL-1 min-1 and 4.75 mM, respectively. These findings evidence a promising novel type II L-asparaginase for future industrial applications.

Heterologous expression and molecular modelling of L-asparaginase from Bacillus subtilis ETMC-2

Bacterial L-asparaginase is the key therapeutic enzyme in cancer therapy and is also witnessing demand as a food processing aid. In this study, L-asparaginase of newly isolated Bacillus subtilis ETMC-2 was cloned and over-expressed in Escherichia coli as an active soluble protein using ligation independent cloning strategy. The molecular mass was estimated to be 40 kDa and was optimally active at 50 °C. Zymography revealed that the enzyme was active in homo-tetramer state (~160 KDa). The encoded protein after BLASTp analysis on NCBI showed 99.73% similarity with L-ASNase that of Bacillus sp. Physico-chemical properties were predicted using Protparam leading to categorization of the enzyme as a stable protein with an instability index (II) of 19.02. The calculated aliphatic index (85.44) indicated the high thermal stability of the protein with GRAVY value of -0.317. Protein-Ligand docking revealed that the residues Thr₈₉, Thr₁₂₁, and Asp₁₂₂ were fundamental in protein-ligand complexation. After homology modelling, model validation was performed using Ramachandran plot, VERIFY3D, and RMSD. The paper describes cloning, heterologous expression, catalytic characteristics and physico-chemical properties of the type II B. subtilis L-ASNase.

[L-asparaginases of extremophilic microorganisms in biomedicine]

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

In silico analysis, molecular cloning, expression and characterization of l-asparaginase gene from Lactobacillus reuteri DSM 20016

l-Asparaginase is employed in leukaemic treatment and in processing starchy foods. The in silico analysis of Lactobacillus reuteri DSM 20016 reveals the presence of an l-asparaginase gene with theoretical pI value of 4.99. 3D structure prediction was carried out and one model was selected based on the validation scores of 86.293 for ERRAT, 92.10% for VERIFY 3D and Ramachandran plot. Multiple sequence alignment of the protein sequences of l-asparaginases I and II of Escherichia coli, Erwinia chrysanthemum and Homo sapiens shows their sequence similarity. The ORF LREU_RS09880 from L. reuteri DSM 20016 genome was cloned and expressed in E. coli. The recombinant protein was purified to homogeneity using Ni-NTA chromatography and showed higher substrate specificity for l-asparagine. Kinetic parameters like K_m and V_max of recombinant l-asparaginase were calculated as 0.3332 mM, 14.06 mM/min, respectively. Temperature and pH profile of recombinant l-asparaginase were analysed and maximum activity was found between 30 and 40 °C and at pH 6. The recombinant enzyme was thermally stable up to 24 h at 28 °C. Recombinant l-asparaginase has a recovery percentage of 92 and 10.5 fold purification. HPLC-MS-MS and SDS-PAGE analysis of the purified protein indicated a molecular weight of 35 kDa as a monomer.

Purification and Characterization of Glutaminase Free Asparaginase from Enterobacter cloacae: In-Vitro Evaluation of Cytotoxic Potential against Human Myeloid Leukemia HL-60 Cells

Asparaginase is an important antileukemic agent extensively used worldwide but the intrinsic glutaminase activity of this enzymatic drug is responsible for serious life threatening side effects. Hence, glutaminase free asparaginase is much needed for upgradation of therapeutic index of asparaginase therapy. In the present study, glutaminase free asparaginase produced from Enterobacter cloacae was purified to apparent homogeneity. The purified enzyme was found to be homodimer of approximately 106 kDa with monomeric size of approximately 52 kDa and pI 4.5. Purified enzyme showed optimum activity between pH 7-8 and temperature 35-40°C, which is close to the internal environment of human body. Monovalent cations such as Na+ and K+ enhanced asparaginase activity whereas divalent and trivalent cations, Ca2+, Mg2+, Zn2+, Mn2+, and Fe3+ inhibited the enzyme activity. Kinetic parameters Km, Vmax and Kcat of purified enzyme were found to be 1.58×10-3 M, 2.22 IU μg-1 and 5.3 × 104 S-1, respectively. Purified enzyme showed prolonged in vitro serum (T1/2 = ~ 39 h) and trypsin (T1/2 = ~ 32 min) half life, which is therapeutically remarkable feature. The cytotoxic activity of enzyme was examined against a panel of human cancer cell lines, HL-60, MOLT-4, MDA-MB-231 and T47D, and highest cytotoxicity observed against HL-60 cells (IC50 ~ 3.1 IU ml-1), which was comparable to commercial asparaginase. Cell and nuclear morphological studies of HL-60 cells showed that on treatment with purified asparaginase symptoms of apoptosis were increased in dose dependent manner. Cell cycle progression analysis indicates that enzyme induces apoptosis by cell cycle arrest in G0/G1 phase. Mitochondrial membrane potential loss showed that enzyme also triggers the mitochondrial pathway of apoptosis. Furthermore, the enzyme was found to be nontoxic for human noncancerous cells FR-2 and nonhemolytic for human erythrocytes.

Effective treatment for suppression of acrylamide formation in fried potato chips using L-asparaginase from Bacillus subtilis

It has been reported that acrylamide, a potential carcinogen, is formed from the reaction of L-asparagine (L-Asn) and reducing sugars contained in foods during heating processes and free asparagine is a limiting factor for acrylamide formation. It has been reported that potato products such as potato chips, which are made through heating processes, contain high levels of acrylamide. To decrease the amount of L-Asn in potatoes using L-asparaginase, effective treatment conditions of sliced potatoes with the enzyme have been investigated. By treating sliced potatoes with Bacillus subtilis L-asparaginase II (BAsnase; 4 U/g potato), appriximately 40 % of L-Asn in the sliced potatoes was converted into L-aspartic acid (L-Asp). To make this enzyme more effective, prior to enzymatic treatment, sliced potatoes were freeze-thawed, dried at 90 °C for 20 min, and vacuum treated for 10 min under decompressed condition, resulting in the hydrolysis of approximately 90 % of L-Asn to L-Asp. The acrylamide content of BAsnase-treated fried potato chips decreased to below 20 % of that of BAsnase-untreated fried potato chips. Treatment conditions examined in this study were found to be effective to suppress the formation of acrylamide in fried potato chips.

Characterization of a recombinant glutaminase-free L-asparaginase (ansA3) enzyme with high catalytic activity from Bacillus licheniformis

L-Asparaginase (3.5.1.1) is an enzyme widely used to treat the acute lymphoblastic leukemia. Two genes coding for L-asparaginase (ansA1 and ansA3) from Bacillus licheniformis MTCC 429 were cloned and overexpressed in Escherichia coli BL21 (DE3) cells. The recombinant proteins were purified to homogeneity by one-step purification process and further characterized for various biochemical parameters. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that both the enzymes are monomers of ∼37 kDa. Recombinant ansA1 was found to be highly unstable, and recombinant ansA3 was catalytically active and stable, which showed an optimum activity of 407.65 IU/mg at 37 °C and pH 8. Recombinant ansA3 showed higher substrate specificity for L-asparagine with negligible glutaminase activity. Kinetic parameters like K m , V max, k cat, and k cat/K m were calculated for recombinant ansA3.

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.

TK1656, a thermostable l-asparaginase from Thermococcus kodakaraensis, exhibiting highest ever reported enzyme activity

Two L-asparaginase homologs, TK1656 and TK2246, have been found in the genome of Thermococcus kodakaraensis. The gene encoding TK1656 consists of 984 nucleotides corresponding to a polypeptide of 328 amino acids. To examine the properties of TK1656, the structural gene was cloned, expressed in Escherichia coli and the purified gene product was characterized. TK1656 exhibited high asparaginase activity (2350 U mg⁻¹) but no glutaminase activity. The enzyme also displayed the D-asparaginase activity but 50% to that of L-asparaginase. The highest activity was observed at 85°C and pH 9.5. TK1656 catalyzed the conversion of L-asparagine to L-aspartatic acid and ammonia following Michaelise-Menten kinetics with a K(m) and V(max) values of 5.5 mM and 3300 mmol min⁻¹ mg⁻¹, respectively. The activation energy from the linear Arrhenius plot was found to be 58 kJ mol⁻¹. Unfolding studies suggested that urea could not induce complete unfolding and inactivation of TK1656 even at a concentration 8 M; however, in the presence of 4 M guanidine hydrochloride enzyme structure was unfolded with complete loss of enzyme activity.