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.

Purification and characterization of thrombin from camel plasma: interaction with camel tick salivary gland thrombin inhibitor

BACKGROUND

Thrombin is the most important enzyme in the hemostatic process by permitting rapid and localized coagulation in case of tissue damage. Camel thrombin is the natural and proper target enzyme for the previously purified camel tick salivary gland thrombin inhibitor.

RESULTS

In this study, the camel thrombin was purified homogenously in a single affinity chromatographic step on the heparin-agarose affinity column with a specific activity of 3242 NIH units/mg proteins. On SDS-PAGE, the purified camel thrombin contained two forms, 37 kDa α-thrombin and 28 kDa β-thrombin, and the camel prothrombin was visualized as 72 kDa. The camel thrombin Km value was found out as 60 µM of N-(p-Tosyl)-Gly-Pro-Arg-p-nitroanilide acetate and displayed its optimum activity at pH 8.3. The PMSF was the most potent inhibitor of camel thrombin. Camel tick salivary gland thrombin inhibitor has two binding sites on camel thrombin and inhibited it competitively with Ki value of 0.45 µM.

CONCLUSIONS

The purified camel thrombin was found to be more susceptible toward the camel tick salivary gland thrombin inhibitor than bovine thrombin.

Thrombin inhibitor from the salivary gland of the camel tick Hyalomma dromedarii

Blood-sucking arthropods have different types of anticoagulants to allow the ingestion of a blood meal from their hosts. In this study, five anticoagulants prolonging the activated partial thromboplastin time were resolved from the salivary gland crude extract of the camel tick Hyalomma dromedarii by chromatography on diethylaminoethyl (DEAE)-cellulose column. They were designated P1, P2, P3, P4 and P5 according to their elution order. P5 was found to be a potent thrombin inhibitor and purified by ultrafiltration through two centrifugal concentrators of 50 and 30 kDa molecular weight cut-off (MWCO), respectively. The camel tick salivary gland thrombin inhibitor was purified 60.6 folds with a specific activity of 564 units/mg protein. It turned out to be homogenous on native-PAGE with molecular weight of 36 kDa as detected on 12% SDS-PAGE. It inhibits bovine thrombin competitively with K _i value of 0.55 μM. A task for the future will be the elucidation of this thrombin inhibitor structure to allow its application in thrombosis treatment.

Catalase from larvae of the camel tick Hyalomma dromedarii

Catalase plays a major role in protecting cells against toxic reactive oxygen species. Here, Catalase was purified from larvae of the camel tick Hyalomma dromedarii and designated TLCAT. It was purified by ammonium sulfate precipitation and chromatography on DEAE-cellulose, Sephacryl S-300 and CM-cellulose columns. Gel filtration and SDS-PAGE of the purified TLCAT indicated that the protein has a native molecular weight of 120 kDa and is most likely a homodimer with a subunit of approximately 60 kDa. The Km value of TLCAT is 12 mM H2O2 and displayed its optimum activity at pH 7.2. CaCl2, MgCl2, MnCl2 and NiCl2 increased the activity of TLCAT, while FeCl2, CoCl2, CuCl2 and ZnCl2 inhibited the activity of TLCAT. Sodium azide inhibited TLCAT competitively with a Ki value of 0.28 mM. The presence of TLCAT in cells may play a role in protecting H. dromedarii ticks against oxidative damage. This finding will contribute to our understanding of the physiology of these ectoparasites and the development of untraditional methods to control them.