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Boophilus microplus anticoagulant protein: an antithrombin inhibitor isolated from the cattle tick saliva
F Horn1, P C dos Santos, C Termignoni
1Centro de Biotecnologia, Departamento de Biofísica, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil. fhorn@dna.cbiot.ufrgs.br
Abstract:
An anticoagulant was isolated from saliva of the cattle tick Boophilus microplus. Crude saliva prolonged both recalcification time and prothrombin time in assays with bovine plasma. It also inhibited thrombin, but not fXa, amidolytic activity. We purified the antithrombin activity by a combination of gel filtration, anion exchange, and affinity chromatography. The purified inhibitor has a molecular weight of 60,000 Da, determined by SDS-PAGE. The anticoagulant IC50 varied from 100 nM to 1.1 microM, depending on the thrombin concentration and substrate used (fibrinogen or platelet receptor). The excess of inhibitor in relation to thrombin indicates that it is not a tight-binding inhibitor. Chromogenic assays using a panel of five serine-proteinases suggest that the inhibitor is specific against thrombin.
Insights
Scientists discovered a novel anticoagulant in cattle tick saliva that specifically inhibits thrombin, offering potential for new blood-thinning therapies.
Area of Science:
- Biochemistry
- Parasitology
- Pharmacology
Background:
- Saliva of the cattle tick *Boophilus microplus* contains bioactive compounds.
- Tick saliva components play roles in host blood feeding and immune evasion.
- Understanding these components can reveal novel therapeutic targets.
Purpose of the Study:
- To isolate and characterize an anticoagulant from *Boophilus microplus* saliva.
- To determine the inhibitory specificity and mechanism of the anticoagulant.
- To evaluate its potential as a therapeutic agent.
Main Methods:
- Crude saliva preparation and anticoagulant activity assays (recalcification time, prothrombin time).
- Purification of the inhibitor using gel filtration, anion exchange, and affinity chromatography.
- Molecular weight determination by SDS-PAGE and enzyme inhibition assays (chromogenic substrate assays).
Main Results:
- Crude saliva exhibited anticoagulant properties, prolonging clotting times and inhibiting thrombin amidolytic activity.
- A 60,000 Da inhibitor was purified with potent anticoagulant activity (IC50 100 nM–1.1 µM).
- The inhibitor demonstrated specificity for thrombin, with no significant inhibition of Factor Xa or other tested serine proteases.
Conclusions:
- A novel, thrombin-specific anticoagulant inhibitor was successfully isolated from *Boophilus microplus* saliva.
- The inhibitor's mechanism is not tight-binding, suggesting a distinct interaction with thrombin.
- This tick-derived anticoagulant represents a promising candidate for developing new antithrombotic drugs.