: A novel Kunitz family protein with versatile functions during feeding and reproduction of the tick .

As obligate blood-feeding ectoparasites, ticks secrete a great diversity of antithrombin molecules during feeding. In this study, a novel antithrombin gene named was characterized from the tick . It has an open reading frame size of 426 bp; it encodes 141 amino acids and has a predicted molecular weight of 15.8 kDa. The fibrinogen coagulation test showed that the time of coagulation was increased significantly with increase in rDoenitin-1 protein concentration, and the activated partial thromboplastin time (APTT) and prothrombin time (PT) assays showed that rDoenitin-1 significantly prolonged the coagulation time of APTT, indicating that rDoenitin-1 has an anticoagulant activity . In addition, rDoenitin-1 presents a significant inhibitory activity in thrombin and cathepsin G. The hemolysis rate of rDoenitin-1 in healthy human blood cells was 4.25%, and no obvious hemolysis activity was observed. The comparison with other life stages shows that the higher expression occurs in adults, and tissue comparison indicated a higher expression in the midgut. The RNAi results indicated that interference of significantly reduced the engorgement rate and egg hatchability of , and that the engorged body weight was slightly reduced. In conclusion, the results suggested that the novel gene functions in blood-feeding of and performs various functions during feeding and reproduction of . may be a potential vaccine candidate for tick control and for developing new antithrombotic drugs in the future.