Structure and function of the thermostableL-asparaginase fromThermococcus kodakarensis

Cloning, Expression, Characterization and in silico studies of l-asparaginase from Vibrio sp. (GBPx3)

l-asparaginase is a critical therapeutic enzyme for treating acute lymphoblastic leukemia (ALL), a common childhood malignancy. In this study, the l-asparaginase coding sequence from halophilic Vibrio sp. (GBPx3) was cloned, expressed in Escherichia coli, and characterized. The enzyme exhibited a molecular weight of 39.2 kDa and demonstrated a Km of 4.517 mM, kcat of 2.88 1/s, and Vmax of 0.1055 μmol/min, reflecting high specificity for l-asparagine and minimal activity (0.4 %) toward l-glutamine. Optimal activity was observed at physiological conditions (37 °C, pH 7.5 and 125-150 mM NaCl), consistent with human serum osmolality. The half-life of the enzyme was 2.64 h in human serum at 37 °C that is longer than the half-life reported for E. colil-asparaginase. Additionally, the enzyme had no toxic impact on human umbilical vein endothelial cells (HUVEC) and human erythrocytes. The recombinant l-asparaginase was predicted to be 29.3 % helix, 35.6 % turns, and 35.1 % random by circular dichroism spectroscopy. AlphaFold predicted a 3D structure with promising validation scores. The molecular docking study showed that Thr14, Ser60, Thr91, and Asp92 are putative active site residues, with a negative binding energy of -4.5 kJ/mol for the substrate-enzyme interaction. The enzyme's low immunogenicity, high serum stability, and reduced glutaminase activity highlight its potential as a safer therapeutic alternative. Future experiments and protein engineering studies are needed to explore enzyme's in vivo efficacy and improve its clinical effectiveness.

Enhancement of isomerization activity and thermostability of cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus using semi-rational design

Cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus (CsCE) is crucial for lactulose production; however, its low isomerization activity and poor thermostability limit its industrial application. Herein, four single-point mutants (S70D, F171W, S173L, and L354F) with significantly improved isomerization activity were obtained using a computer-aided semi-rational design, and combined mutants were introduced. The isomerization specific activities of the mutants CsCE-F171W/S173L/L354F and CsCE-S70D/F171W/S173L/L354F were 2.10 and 2.05 times higher than that of wild-type CsCE, respectively. Enzymatic properties revealed that the mutant CsCE-F171W/S173L/L354F demonstrated a 2.50-fold increase in t1/2 at 80 °C and a 2.70-fold improvement in kcat, while the mutant CsCE-S70D/F171W/S173L/L354F exhibited a 2.91-fold increase in t1/2 at 80 °C and a 3.19-fold improvement in kcat. Three-dimensional structural analysis suggested that conformational changes in the flexible ring induced by mutation could enhance isomerization activity, while increased structural rigidity, hydrophobic contacts, van der Waals forces, and favorable electrostatic potentials may promote thermostability. These findings provide novel insights into the molecular modification of CsCE and significantly enhance its potential for industrial applications.

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.

Engineering Tk1656, a highly active l-asparaginase from Thermococcus kodakarensis, for enhanced activity and stability

l-Asparaginases catalyze the hydrolysis of l-asparagine to l-aspartic acid and ammonia. These enzymes have potential applications in therapeutics and food industry. Tk1656, a highly active and thermostable l-asparaginase from Thermococcus kodakarensis, has been proved effective in selective killing of acute lymphocytic leukemia cells and in reducing acrylamide formation in baked and fried foods. However, it displayed <5 % activity under physiological conditions compared to the optimal activity at 85 °C and pH 9.5. We have attempted engineering of this valuable enzyme to improve the characteristics required for therapeutic and industrial applications. Based on the literature and crystal structure of Tk1656, nine specific mutant variants were designed, produced in Escherichia coli, and the purified mutant enzymes were compared with the wild-type. One of the mutants, K299L, displayed >20 % increase in activity at 85 °C. H158S substitution resulted in >5 °C increase in the optimal temperature. Similarly, a mesophilic-like mutation L56D, resulted in >5-fold increase in activity at pH 7.0 and 37 °C compared to that of the wild-type enzyme. The substrate specificity of the mutant variants remained unchanged. These results demonstrate that L56D and K299L variants of Tk1656 are the potent enzymes for therapeutics and acrylamide mitigation applications, respectively.

Towards a dependable data set of structures for L-asparaginase research

The Protein Data Bank (PDB) includes a carefully curated treasury of experimentally derived structural data on biological macromolecules and their various complexes. Such information is fundamental for a multitude of projects that involve large-scale data mining and/or detailed evaluation of individual structures of importance to chemistry, biology and, most of all, to medicine, where it provides the foundation for structure-based drug discovery. However, despite extensive validation mechanisms, it is almost inevitable that among the ∼215 000 entries there will occasionally be suboptimal or incorrect structure models. It is thus vital to apply careful verification procedures to those segments of the PDB that are of direct medicinal interest. Here, such an analysis was carried out for crystallographic models of L-asparaginases, enzymes that include approved drugs for the treatment of certain types of leukemia. The focus was on the adherence of the atomic coordinates to the rules of stereochemistry and their agreement with the experimental electron-density maps. Whereas the current clinical application of L-asparaginases is limited to two bacterial proteins and their chemical modifications, the field of investigations of such enzymes has expanded tremendously in recent years with the discovery of three entirely different structural classes and with numerous reports, not always quite reliable, of the anticancer properties of L-asparaginases of different origins.

A novel type IIb L-asparaginase from Latilactobacillus sakei LK-145: characterization and application

We succeeded in homogeneously expressing and purifying L-asparaginase from Latilactobacillus sakei LK-145 (Ls-Asn1) and its mutated enzymes C196S, C264S, C290S, C196S/C264S, C196S/C290S, C264S/C290S, and C196S/C264S/C290S-Ls-Asn1. Enzymological studies using purified enzymes revealed that all cysteine residues of Ls-Asn1 were found to affect the catalytic activity of Ls-Asn1 to varying degrees. The mutation of Cys196 did not affect the specific activity, but the mutation of Cys264, even a single mutation, significantly decreased the specific activity. Furthermore, C264S/C290S- and C196S/C264S/C290S-Ls-Asn1 almost completely lost their activity, suggesting that C290 cooperates with C264 to influence the catalytic activity of Ls-Asn1. The detailed enzymatic properties of three single-mutated enzymes (C196S, C264S, and C290S-Ls-Asn1) were investigated for comparison with Ls-Asn1. We found that only C196S-Ls-Asn1 has almost the same enzymatic properties as that of Ls-Asn1 except for its increased stability for thermal, pH, and the metals NaCl, KCl, CaCl2, and FeCl2. We measured the growth inhibitory effect of Ls-Asn1 and C196S-Ls-Asn1 on Jurkat cells, a human T-cell acute lymphoblastic leukemia cell line, using L-asparaginase from Escherichia coli K-12 as a reference. Only C196S-Ls-Asn1 effectively and selectively inhibited the growth of Jurkat T-cell leukemia, which suggested that it exhibited antileukemic activity. Furthermore, based on alignment, phylogenetic tree analysis, and structural modeling, we also proposed that Ls-Asn1 is a so-called "Type IIb" novel type of asparaginase that is distinct from previously reported type I or type II asparaginases. Based on the above results, Ls-Asn1 is expected to be useful as a new leukemia therapeutic agent.

L-Asparaginase Conjugates from the Hyperthermophilic Archaea Thermococcus sibiricus with Improved Biocatalytic Properties

This study investigated the effect of polycationic and uncharged polymers (and oligomers) on the catalytic parameters and thermostability of L-asparaginase from Thermococcus sibiricus (TsA). This enzyme has potential applications in the food industry to decrease the formation of carcinogenic acrylamide during the processing of carbohydrate-containing products. Conjugation with the polyamines polyethylenimine and spermine (PEI and Spm) or polyethylene glycol (PEG) did not significantly affect the secondary structure of the enzyme. PEG contributes to the stabilization of the dimeric form of TsA, as shown by HPLC. Furthermore, neither polyamines nor PEG significantly affected the binding of the L-Asn substrate to TsA. The conjugates showed greater maximum activity at pH 7.5 and 85 °C, 10-50% more than for native TsA. The pH optima for both TsA-PEI and TsA-Spm conjugates were shifted to lower pH ranges from pH 10 (for the native enzyme) to pH 8.0. Additionally, the TsA-Spm conjugate exhibited the highest activity at pH 6.5-9.0 among all the samples. Furthermore, the temperature optimum for activity at pH 7.5 shifted from 90-95 °C to 80-85 °C for the conjugates. The thermal inactivation mechanism of TsA-PEG appeared to change, and no aggregation was observed in contrast to that of the native enzyme. This was visually confirmed and supported by the analysis of the CD spectra, which remained almost unchanged after heating the conjugate solution. These results suggest that TsA-PEG may be a more stable form of TsA, making it a potentially more suitable option for industrial use.

RrA, an enzyme from Rhodospirillum rubrum, is a prototype of a new family of short-chain L-asparaginases

L-Asparaginases (ASNases) catalyze the hydrolysis of L-Asn to L-Asp and ammonia. Members of the ASNase family are used as drugs in the treatment of leukemia, as well as in the food industry. The protomers of bacterial ASNases typically contain 300-400 amino acids (typical class 1 ASNases). In contrast, the chain of ASNase from Rhodospirillum rubrum, reported here and referred to as RrA, consists of only 172 amino acid residues. RrA is homologous to the N-terminal domain of typical bacterial class 1 ASNases and exhibits millimolar affinity for L-Asn. In this study, we demonstrate that RrA belongs to a unique family of cytoplasmic, short-chain ASNases (scASNases). These proteins occupy a distinct region in the sequence space, separate from the regions typically assigned to class 1 ASNases. The scASNases are present in approximately 7% of eubacterial species, spanning diverse bacterial lineages. They seem to be significantly enriched in species that encode for more than one class 1 ASNase. Here, we report biochemical, biophysical, and structural properties of RrA, a member of scASNases family. Crystal structures of the wild-type RrA, both with and without bound L-Asp, as well as structures of several RrA mutants, reveal topologically unique tetramers. Moreover, the active site of one protomer is complemented by two residues (Tyr21 and Asn26) from another protomer. Upon closer inspection, these findings clearly outline scASNases as a stand-alone subfamily of ASNases that can catalyze the hydrolysis of L-Asn to L-Asp despite the lack of the C-terminal domain that is present in all ASNases described structurally to date.

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.

Rational engineering and insight for a L-glutaminase activity reduced type II L-asparaginase from Bacillus licheniformis and its antileukemic activity in vitro

Type II L-asparaginase (ASNase) has been approved by the FDA for treating acute lymphoid leukemia (ALL), but its therapeutic effect is limited by low catalytic efficiency and L-glutaminase (L-Gln) activity. This study utilized free energy based molecular dynamics calculations to identify residues associated with substrate binding in Bacillus licheniformis L-asparaginase II (BLASNase) with high catalytical activity. After saturation and combination mutagenesis, the mutant LGT (74 L/75G/111 T) with intensively reduced l-glutamine catalytic activity was generated. The l-glutamine/L-asparagine activity (L-Gln/L-Asn) of LGT was only 6.6 % of parent BLASNase, whereas the L-asparagine (L-Asn) activity was preserved >90 %. Furthermore, structural comparison and molecular dynamics calculations indicated that the mutant LGT had reduced binding ability and affinity towards l-glutamine. To evaluate its effect on acute leukemic cells, LGT was supplied in treating MOLT-4 cells. The experimental results demonstrated that LGT was more cytotoxic and promoted apoptosis compared with commercial Escherichia coli ASNase. Overall, our findings firstly provide insights into reducing l-glutamine activity without impacting L-asparagine activity for BLASNase to possess remarkable potential for anti-leukemia therapy.

Enhancing the Catalytic Activity of Thermo-Asparaginase from Thermococcus sibiricus by a Double Mesophilic-like Mutation in the Substrate-Binding Region

L-asparaginases (L-ASNases) of microbial origin are the mainstay of blood cancer treatment. Numerous attempts have been performed for genetic improvement of the main properties of these enzymes. The substrate-binding Ser residue is highly conserved in L-ASNases regardless of their origin or type. However, the residues adjacent to the substrate-binding Ser differ between mesophilic and thermophilic L-ASNases. Based on our suggestion that the triad, including substrate-binding Ser, either GSQ for meso-ASNase or DST for thermo-ASNase, is tuned for efficient substrate binding, we constructed a double mutant of thermophilic L-ASNase from Thermococcus sibiricus (TsA) with a mesophilic-like GSQ combination. In this study, the conjoint substitution of two residues adjacent to the substrate-binding Ser55 resulted in a significant increase in the activity of the double mutant, reaching 240% of the wild-type enzyme activity at the optimum temperature of 90 °C. The mesophilic-like GSQ combination in the rigid structure of the thermophilic L-ASNase appears to be more efficient in balancing substrate binding and conformational flexibility of the enzyme. Along with increased activity, the TsA D54G/T56Q double mutant exhibited enhanced cytotoxic activity against cancer cell lines with IC90 values from 2.8- to 7.4-fold lower than that of the wild-type enzyme.

Computational Insights and In Silico Characterization of a Novel Mini-Lipoxygenase from Nostoc Sphaeroides and Its Application in the Quality Improvement of Steamed Bread

Lipoxygenase (EC1.13.11.12, LOX) has been potentially used in the food industry for food quality improvement. However, the low activity, poor thermal stability, narrow range of pH stability, as well as undesirable isoenzymes and off-flavors, have hampered the application of current commercial LOX. In this study, a putative mini-lipoxygenase gene from cyanobacteria, Nostoc sphaeroides (NsLOX), was cloned and expressed in E. coli BL21. NsLOX displayed only 26.62% structural identity with the reported LOX from Cyanothece sp., indicating it as a novel LOX. The purified NsLOX showed the maximum activity at pH 8.0 and 15 °C, with superior stability at a pH range from 6.0 to 13.0, retaining about 40% activity at 40 °C for 90 min. Notably, NsLOX exhibited the highest specific activity of 78,080 U/mg towards linoleic acid (LA), and the kinetic parameters-K_m, k_cat, and k_cat/K_m-attain values of 19.46 μM, 9199.75 s^-1, and 473.85 μM^-1 s^-1, respectively. Moreover, the activity of NsLOX was obviously activated by Ca²⁺, but it was completely inhibited by Zn²⁺ and Cu²⁺. Finally, NsLOX was supplied in steamed bread and contributed even better improved bread quality than the commercial LOX. These results suggest NsLOX as a promising substitute of current commercial LOX for application in the food industry.

Thermostability enhancement and insight of L-asparaginase from Mycobacterium sp. via consensus-guided engineering

Acrylamide alleviation in food has represented as a critical issue due to its neurotoxic effect on human health. L-Asparaginase (ASNase, EC 3.5.1.1) is considered a potential additive for acrylamide alleviation in food. However, low thermal stability hinders the application of ASNase in thermal food processing. To obtain highly thermal stable ASNase for its industrial application, a consensus-guided approach combined with site-directed saturation mutation (SSM) was firstly reported to engineer the thermostability of Mycobacterium gordonae L-asparaginase (GmASNase). The key residues Gly97, Asn159, and Glu249 were identified for improving thermostability. The combinatorial triple mutant G97T/N159Y/E249Q (TYQ) displayed significantly superior thermostability with half-life values of 61.65 ± 8.69 min at 50 °C and 5.12 ± 1.66 min at 55 °C, whereas the wild-type was completely inactive at these conditions. Moreover, its T_m value increased by 8.59 °C from parent wild-type. Interestingly, TYQ still maintained excellent catalytic efficiency and specific activity. Further molecular dynamics and structure analysis revealed that the additional hydrogen bonds, increased hydrophobic interactions, and favorable electrostatic potential were essential for TYQ being in a more rigid state for thermostability enhancement. These results suggested that our strategy was an efficient engineering approach for improving fundamental properties of GmASNase and offering GmASNase as a potential agent for efficient acrylamide mitigation in food industry. KEY POINTS: • The thermostability of GmASNase was firstly improved by consensus-guided engineering. • The half-life and T_m value of triple mutant TYQ were significantly increased. • Insight on improved thermostability of TYQ was revealed by MD and structure analysis.

Enhanced Thermostability and Molecular Insights for l-Asparaginase from Bacillus licheniformis via Structure- and Computation-Based Rational Design

l-Asparaginase has gained much attention for effectively treating acute lymphoblastic leukemia (ALL) and mitigating carcinogenic acrylamide in fried foods. Due to high-dose dependence for clinical treatment and low mitigation efficiency for thermal food processes caused by poor thermal stability, a method to achieve thermostable l-asparaginase has become a critical bottleneck. In this study, a rational design including free energy combined with structural and conservative analyses was applied to engineer the thermostability of l-asparaginase from Bacillus licheniformis (BlAsnase). Two enhanced thermostability mutants D172W and E207A were screened out by site-directed saturation mutagenesis. The double mutant D172W/E207A exhibited highly remarkable thermostability with a 65.8-fold longer half-life at 55 °C and 5 °C higher optimum reaction temperature and melting temperature (T_m) than those of wild-type BlAsnase. Further, secondary structure, sequence, molecular dynamics (MD), and 3D-structure analysis revealed that the excellent thermostability of the mutant D172W/E207A was on account of increased hydrophobicity and decreased flexibility, highly rigid structure, hydrophobic interactions, and favorable electrostatic potential. As the first report of rationally designing l-asparaginase with improved thermostability from B. licheniformis, this study offers a facile and efficient process to improve the thermostability of l-asparaginase for industrial applications.

Insights into the Distribution and Functional Properties of l-Asparaginase in the Archaeal Domain and Characterization of Picrophilus torridus Asparaginase Belonging to the Novel Family Asp2like1

l-Asparaginase catalyzes the hydrolysis of l-asparagine to aspartic acid and ammonia and is used in the medical and food industries. In this investigation, from the proteomes of 176 archaeal organisms (with completely sequenced genomes), 116 homologs of l-asparaginase were obtained from 86 archaeal organisms segregated into Asp1, Asp2, IaaA, Asp2like1, and Asp2like2 families based on the conserved domain. The similarities and differences in the structure of selected representatives from each family are discussed. From the two novel archaeal l-asparaginase families Asp2like1 and Asp2like2, a representative of Asp2like1 family Picrophilus torridus asparaginase (PtAsp2like1) was characterized in detail to find its suitability in therapeutics. PtAsp2like1 was a glutaminase-free asparaginase that showed the optimum activity at 80 °C and pH 10.0. The Km of PtAsp2like1 toward substrate l-asparagine was 11.69 mM. This study demonstrates the improved mapping of asparaginases in the archaeal domain, facilitating future focused research on archaeal asparaginases for therapeutic applications.

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.

Highly Active Thermophilic L-Asparaginase from Melioribacter roseus Represents a Novel Large Group of Type II Bacterial L-Asparaginases from Chlorobi-Ignavibacteriae-Bacteroidetes Clade

L-asparaginase (L-ASNase) is a biotechnologically relevant enzyme for the pharmaceutical, biosensor and food industries. Efforts to discover new promising L-ASNases for different fields of biotechnology have turned this group of enzymes into a growing family with amazing diversity. Here, we report that thermophile Melioribacter roseus from Ignavibacteriae of the Bacteroidetes/Chlorobi group possesses two L-ASNases-bacterial type II (MrAII) and plant-type (MrAIII). The current study is focused on a novel L-ASNase MrAII that was expressed in Escherichia coli, purified and characterized. The enzyme is optimally active at 70 °C and pH 9.3, with a high L-asparaginase activity of 1530 U/mg and L-glutaminase activity ~19% of the activity compared with L-asparagine. The kinetic parameters KM and Vmax for the enzyme were 1.4 mM and 5573 µM/min, respectively. The change in MrAII activity was not significant in the presence of 10 mM Ni2+, Mg2+ or EDTA, but increased with the addition of Cu2+ and Ca2+ by 56% and 77%, respectively, and was completely inhibited by Zn2+, Fe3+ or urea solutions 2-8 M. MrAII displays differential cytotoxic activity: cancer cell lines K562, Jurkat, LnCap, and SCOV-3 were more sensitive to MrAII treatment, compared with normal cells. MrAII represents the first described enzyme of a large group of uncharacterized counterparts from the Chlorobi-Ignavibacteriae-Bacteroidetes clade.

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

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

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.

The X-ray structure of L-threonine dehydrogenase from the common hospital pathogen Clostridium difficile

In many prokaryotes, the first step of threonine metabolism is catalysed by the enzyme threonine dehydrogenase (TDH), which uses NAD+ to oxidize its substrate to 2-amino-3-ketobutyrate. The absence of a functional TDH gene in humans suggests that inhibitors of this enzyme may have therapeutic potential against pathogens which are reliant on this enzyme. Here, TDH from Clostridium difficile has been cloned and overexpressed, and the X-ray structure of the apoenzyme form has been determined at 2.6 Å resolution.

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.

Structural and biochemical properties of L-asparaginase

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

Studies on the recombinant production and anticancer activity of thermostable L- asparaginase I from Pyrococcus abyssi

L-Asparaginase catalysing the breakdown of L-Asparagine to L-Aspartate and ammonia is an enzyme of therapeutic importance in the treatment of cancer, especially the lymphomas and leukaemia. The present study describes the recombinant production, properties and anticancer potential of enzyme from a hyperthermophilic archaeon Pyrococcus abyssi. There are two genes coding for asparaginase in the genome of this organism. A 918 bp gene encoding 305 amino acids was PCR amplified and cloned in BL21 (DE3) strain of E. coli using pET28a (+) plasmid. The production of recombinant enzyme was induced under 0.5mM IPTG, purified by selective heat denaturation and ion exchange chromatography. Purified enzyme was analyzed for kinetics, in silico structure and anticancer properties. The recombinant enzyme has shown a molecular weight of 33 kDa, specific activity of 1175 U/mg, KM value 2.05mM, optimum temperature and pH 80°C and 8 respectively. No detectable enzyme activity found when L-Glutamine was used as the substrate. In silico studies have shown that the enzyme exists as a homodimer having Arg11, Ala87, Thr110, His112, Gln142, Leu172, and Lys232 being the putative active site residues. The free energy change calculated by molecular docking studies of enzyme and substrate was found as ∆G - 4.5 kJ/mole indicating the affinity of enzyme with the substrate. IC50 values of 5U/mL to 7.5U/mL were determined for FB, caco2 cells and HepG2 cells. A calculated amount of enzyme (5U/mL) exhibited 78% to 55% growth inhibition of caco2 and HepG2 cells. In conclusion, the recombinant enzyme produced and characterized in the present study offers a good candidate for the treatment of cancer. The procedures adopted in the present study can be prolonged for in vivo studies.

Functional and structural investigation of a novel β-mannanase BaMan113A from Bacillus sp. N16-5

Mannan is an important renewable resource whose backbone can be hydrolyzed by β-mannanases to generate manno-oligosaccharides of various sizes. Only a few glycoside hydrolase (GH) 113 family β-mannanases have been functionally and structurally characterize. Here, we report the function and structure of a novel GH113 β-mannanase from Bacillus sp. N16-5 (BaMan113A). BaMan113A exhibits a substrate preference toward manno-oligosaccharides and releases mannose and mannobiose as main hydrolytic products. The crystal structure of BaMan113A suggest that the enzyme shows a semi-enclosed substrate-binding cleft and the amino acids surrounding the +2 subsite form a steric barrier to terminate the substrate-binding tunnel. Based on these structural features, we conducted mutagenesis to engineer BaMan113A to remove the steric hindrance of the substrate-binding tunnel. We found that F101E and N236Y variants exhibit increased specific activity toward mannans comparing to the wild-type enzyme. Meanwhile, the product profiles of these two variants toward polysaccharides changed from mannose to a series of manno-oligosaccharides. The crystal structure of variant N236Y was also determined to illustrate the molecular basis underlying the mutation. In conclusion, we report the functional and structural features of a novel GH113 β-mannanase, and successfully improved its endo-acting activity by using structure-based engineering.

Structures of l-asparaginase from Bacillus licheniformis Reveal an Essential Residue for its Substrate Stereoselectivity

l-Asparaginase, which catalyzes the hydrolysis of l-asparagine, is an important enzyme in both the clinical and food industry. Exploration of efficient l-asparaginase with high substrate specificity, especially high chiral selectivity, is essential for extending its use. Herein, various crystal structures of type I l-asparaginase from Bacillus licheniformis (BlAsnase) have been resolved, and we found that there are two additional tyrosines in BlAsnase, contributing to the binding and catalysis of d-asparagine. Strikingly, the substitution of Tyr278 with methionine impaired the interaction with d-asparagine via water molecules due to the small hydrophobic side chain of methionine, which forced the ligand to the deep side of the active site toward the catalytic residues and thus resulted in the loss of hydrolyzing function. Our investigation of the substrate recognition mechanism of BlAsnase is significant for both a better understanding of l-asparaginase and its rational design to achieve high specificity for clinical and industrial applications.

Diverse Enzymes With Industrial Applications in Four Thraustochytrid Genera

Thraustochytrids are heterotrophic fungus-like protists that can dissolve organic matters with enzymes. Four strains, AP45, ASP1, ASP2, and ASP4, were isolated from the coastal water of Taiwan, and respectively identified as Aurantiochytrium sp., Schizochytrium sp., Parietichytrium sp., and Botryochytrium sp. based on 18S rRNA sequences. Transcriptome datasets of these four strains at days 3-5 were generated using Next Generation Sequencing technology, and screened for enzymes with potential industrial applications. Functional annotations based on KEGG database suggest that many unigenes of all four strains were related to the pathways of industrial enzymes. Most of all four strains contained homologous genes for 15 out of the 17 targeted enzymes, and had extra- and/or intra-cellular enzymatic activities, including urease, asparaginase, lipase, glucosidase, alkaline phosphatase and protease. Complete amino sequences of the first-time identified L-asparaginase and phytase in thraustochytrids were retrieved, and respectively categorized to the Type I and BPPhy families based on phylogenetic relationships, protein structural modeling and active sites. Milligram quantities of highly purified, soluble protein of urease and L-asparaginase were successfully harvested and analyzed for recombinant enzymatic activities. These analytical results highlight the diverse enzymes for wide-range applications in thraustochytrids.

Bacillus sonorensis L. Asparaginase: Cloning, Expression in E. coli and Characterization

L-asparaginases (L-ASNases; EC 3.5.1.1) are aminohydrolases that catalyze the hydrolysis of L-asparagine (L-Asn) to L-aspartic acid and ammonia, resulting in the death of acute lymphoblastic leukemic cells and other blood cancer cells. In this study, Bacillus sonorensis (accession number MK523484) uncharacterized L-ASNase gene (accession number MN562875) was isolated by polymerase chain reaction (PCR), cloned into pET28a (+) vector, and expressed in Escherichia coli as a cytosolic protein. The recombinant enzyme was purified by affinity chromatography at 23.79-fold and 49.37% recovery. Denaturing polyacrylamide gel (10%) analysis of the purified enzyme resulted in a single protein band at 36 kDa that immunoreacted strongly with 6His-tag monoclonal antibody. The purified enzyme exhibited optimal activity at 45 °C and pH 7.0 and retained 92% and 85% of its initial activity after incubation for 60 min at 37 °C and 45 °C, respectively. The purified enzyme exhibited substrate specificity toward L-asparagine and low glutaminase activity (15.72%) toward L-glutamine at a concentration of 10 mM. The Km and Vmax values were 2.004 mM and 3723 µmol min^1-, respectively.

Improving the Treatment of Acute Lymphoblastic Leukemia

l-Asparaginase (EC 3.5.1.1) was first used as a component of combination drug therapies to treat acute lymphoblastic leukemia (ALL), a cancer of the blood and bone marrow, almost 50 years ago. Administering this enzyme to reduce asparagine levels in the blood is a cornerstone of modern clinical protocols for ALL; indeed, this remains the only successful example of a therapy targeted against a specific metabolic weakness in any form of cancer. Three problems, however, constrain the clinical use of l-asparaginase. First, a type II bacterial variant of l-asparaginase is administered to patients, the majority of whom are children, which produces an immune response thereby limiting the time over which the enzyme can be tolerated. Second, l-asparaginase is subject to proteolytic degradation in the blood. Third, toxic side effects are observed, which may be correlated with the l-glutaminase activity of the enzyme. This Perspective will outline how asparagine depletion negatively impacts the growth of leukemic blasts, discuss the structure and mechanism of l-asparaginase, and briefly describe the clinical use of chemically modified forms of clinically useful l-asparaginases, such as Asparlas, which was recently given FDA approval for use in children (babies to young adults) as part of multidrug treatments for ALL. Finally, we review ongoing efforts to engineer l-asparaginase variants with improved therapeutic properties and briefly detail emerging, alternate strategies for the treatment of forms of ALL that are resistant to asparagine depletion.

[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.

Opportunistic complexes of E. coli L-asparaginases with citrate anions

Active sites of enzymes are highly optimized for interactions with specific substrates, thus binding of opportunistic ligands is usually observed only in the absence of native substrates or products. However, during growth of crystals required for structure determination enzymes are often exposed to conditions significantly divergent from the native ones, leading to binding of unexpected ligands to active sites even in the presence of substrates. Failing to recognize this possibility may lead to incorrect interpretation of experimental results and to faulty conclusions. Here, we present several examples of binding of a citrate anion to the active sites of E. coli L-asparaginases I and II, even in the presence of the native substrate, L-Asn. A part of this report focuses on a comprehensive re-interpretation of structural results published previously for complexes of type I L-asparaginase (EcAI) from E. coli. In two re-refined structures a citrate anion forms an acyl-enzyme reaction intermediate with the catalytic threonine. These results emphasize the importance of careful and critical analysis during interpretation of crystallographic data.

An overview of 25 years of research on Thermococcus kodakarensis, a genetically versatile model organism for archaeal research

Almost 25 years have passed since the discovery of a planktonic, heterotrophic, hyperthermophilic archaeon named Thermococcus kodakarensis KOD1, previously known as Pyrococcus sp. KOD1, by Imanaka and coworkers. T. kodakarensis is one of the most studied archaeon in terms of metabolic pathways, available genomic resources, established genetic engineering techniques, reporter constructs, in vitro transcription/translation machinery, and gene expression/gene knockout systems. In addition to all these, ease of growth using various carbon sources makes it a facile archaeal model organism. Here, in this review, an attempt is made to reflect what we have learnt from this hyperthermophilic archaeon.