Anticoagulant protein that may inhibit thrombin by binding to its exosite I. Also inhibits the amidolytic activity of trypsin (tested on the substrate S-2238). The recombinant protein delays plasma clotting time and inhibits both thrombin-induced fibrinogen clotting and thrombin-induced platelet aggregation in a dose-dependent manner. May be an anticoagulant for the common pathway of blood coagulation. Expressed in the major tissues of the adult female tick, including the midgut (highest expression), salivary glands, ovaries, hemolymph, and fat bodies. Expressed at larval, nymphal, and adult stages of fed and unfed ticks, but not expressed at the egg stage. Has the highest expression in the rapid blood meal sucking period (3-4 days after feeding) of all the stages. After gene silencing by RNA interference, the tick attachment time is prolonged and about 25% of RNA-treated ticks do not successfully complete the blood feeding and detach from the host. No significant difference is observed in the engorgement body, egg weight, and hatching capability of eggs.