Purification, characterization, and enzyme kinetics of a glutathione S transferase from larvae of the camel tick Hyalomma dromedarii

BACKGROUND

Glutathione s-transferases (GSTs) perform an essential role in detoxification of xenobiotics and endogenous compounds via their conjugation to reduce glutathione.

RESULTS

A GST enzyme, designated tick larvae glutathione S transferase (TLGST), was purified from larvae of the camel tick Hyalomma dromedarii via ammonium sulfate precipitation, glutathione-Sepharose affinity column and Sephacryl S-300 chromatography. TLGST-specific activity was found to be 1.56 Umg-1 which represents 39 folds and 32.2% recovery. The molecular weight of TLGST purified from camel tick larvae was found as 42 kDa by gel filtration. TLGST has a pI value of 6.9 and was found a heterodimeric protein of 28 and 14 kDa subunits as detected on SDS-PAGE. The Lineweaver-Burk plot calculated the km for CDNB to be 0.43 mM with Vmax value of 9.2 Umg-1. TLGST exhibited its optimal activity at pH 7.9. Co2+, Ni2+ and Mn2+ increased the activity of TLGST while Ca2+, Cu2+, Fe2+ and Zn2+ inhibited it. TLGST was inhibited by cumene hydroperoxide, p-hydroxymercuribenzoate, lithocholic acid, hematin, triphenyltin chloride, p-chloromercuribenzoic acid (pCMB), N-p-Tosyl-L-phenylalanine chloromethyl ketone (TPCK), iodoacetamide, EDTA and quercetin. pCMB inhibited TLGST competitively with Ki value of 0.3 mM.

CONCLUSIONS

These findings will help to understand the various physiologic conditions of ticks and targeting TLGST could be significant tool for development of prospective vaccines against ticks as a bio-control strategy to overcome the rapid grows in pesticide-resistant tick populations.

Apyrase with anti-platelet aggregation activity from the nymph of the camel tick Hyalomma dromedarii

Apyrase is one of the essential platelet aggregation inhibitors in hematophagous arthropods due to its ability to hydrolyze ATP and ADP molecules. Here, an apyrase (TNapyrase) with antiplatelet aggregation activity was purified and characterized from the nymphs of the camel tick Hyalomma dromedarii through anion exchange and gel filtration columns. The homogeneity of TNapyrase was confirmed by native-PAGE, SDS-PAGE as well as with isoelectric focusing. Purified TNapyrase had a molecular mass of 25 kDa and a monomer structure. TNapyrase hydrolyzed various nucleotides in the order of ATP > PPi > ADP > UDP > 6GP. The K_m value was 1.25 mM ATP and its optimum activity reached at pH 8.4. The influence of various ions on TNapyrase activity showed that FeCl₂, FeCl₃ and ZnCl₂ are activators of TNapyrase. EDTA inhibited TNapyrase activity competitively with a single binding site on the molecule and K_i value of 2 mM. Finally, TNapyrase caused 70% inhibition of ADP-stimulated platelets aggregation and is a possible target for antibodies in future tick vaccine studies.

Stress-Based Production, and Characterization of Glutathione Peroxidase and Glutathione S-Transferase Enzymes From Lactobacillus plantarum

More attention has been recently directed toward glutathione peroxidase and s-transferase enzymes because of the great importance they hold with respect to their applications in the pharmaceutical field. This work was conducted to optimize the production and characterize glutathione peroxidase and glutathione s-transferase produced by Lactobacillus plantarum KU720558 using Plackett-Burman and Box-Behnken statistical designs. To assess the impact of the culture conditions on the microbial production of the enzymes, colorimetric methods were used. Following data analysis, the optimum conditions that enhanced the s-transferase yield were the De Man-Rogosa-Sharp (MRS) broth as a basal medium supplemented with 0.1% urea, 0.075% H₂O₂, 0.5% 1-butanol, 0.0125% amino acids, and 0.05% SDS at pH 6.0 and anaerobically incubated for 24 h at 40°C. The optimum s-transferase specific activity was 1789.5 U/mg of protein, which was ~12 times the activity of the basal medium. For peroxidase, the best medium composition was 0.17% urea, 0.025% bile salt, 7.5% Na Cl, 0.05% H₂O₂, 0.05% SDS, and 2% ethanol added to the MRS broth at pH 6.0 and anaerobically incubated for 24 h at 40°C. Furthermore, the optimum peroxidase specific activity was 612.5 U/mg of protein, indicating that its activity was 22 times higher than the activity recorded in the basal medium. After SDS-PAGE analysis, GST and GPx showed a single protein band of 25 and 18 kDa, respectively. They were able to retain their activities at an optimal temperature of 40°C for an hour and pH range 4–7. The 3D model of both enzymes was constructed showing helical structures, sheet and loops. Protein cavities were also detected to define druggable sites. GST model had two large pockets; 185Å3 and 71 Å3 with druggability score 0.5–0.8. For GPx, the pockets were relatively smaller, 71 Å3 and 32 Å3 with druggability score (0.65–0.66). Therefore, the present study showed that the consortium components as well as the stress-based conditions used could express both enzymes with enhanced productivity, recommending their application based on the obtained results.

A glutathione peroxidase from Antarctic psychrotrophic bacterium Pseudoalteromonas sp. ANT506: Cloning and heterologous expression of the gene and characterization of recombinant enzyme

A glutathione peroxidase (GPx) gene, designated as PsGPx, was cloned from Antarctic psychrotrophic bacterium Pseudoalteromonas sp. ANT506 and expressed in Escherichia coli. The full-length PsGPx contained a 585-bp encoding 194 amino acids with predicted molecular masses of approx. 21.7 kDa. Multiple sequence alignments revealed that PsGPx belonged to the thioredoxin-like superfamily. PsGPx was heterologously overexpressed in E. coli, purified and characterized. The maximum catalytic temperature and pH value for recombinant PsGPx (rPsGPx) were 30°C and pH 9.0, respectively. rPsGPx retained 45% of the maximum activity at 0°C and exhibited high thermolability with a half-life of approx. 40 min at 40°C. In addition, the enzymatic activity of rPsGPx was still manifested under 3 M NaCl. The K_m and V_max values of the recombinant enzyme using GSH and H₂O₂ as substrates were 1.73 mM and 16.28 nmol/mL/min versus 2.46 mM and 21.50 nmol/mL/min, respectively.