A double headed serine proteinase inhibitor - human plasma kallikrein and elastase inhibitor - from Boophilus microplus larvae

Preying on cattle, the hard tick Boophilus microplus causes heavy economica l losses to Brazil. Tick proteins are a good target to be used as tools for tick control. Serine protease inhibitors from B. microplus larvae (BmTI) w ere preliminarily characterized. One-week-old larvae were the source of a 2 % protein solution in 5 mM Tris-HCl, 20 mM NaCl, pH 7.4. The inhibitors wer e purified by affinity chromatography on trypsin-Sepharose, and ion-exchang e chromatography on Resource Q column, and they separated in two major acti ve peaks, corresponding to 10-kDa and 18-kDa proteins (BmTI-B and BmTI-A, r espectively). Both purified proteins inhibited trypsin with K-i of 0.3 and 3.0 nM, respectively, but only the 18-kDa protein inhibited elastase (K-i 1 .4 nM) and plasma kallikrein (K-i 120 nM). BmTI-A did not change prothrombi n time (PT) and thrombin time (TT), but it increased activated partial thro mboplastin time (APTT) was dose-dependent. The partial amino acid sequence indicated that BmTI-A belongs to the bovine pancreatic trypsin inhibitor (B PTI)-Kunitz type inhibitor family. These inhibitors (by their properties) p lay a role in the feeding process of the tick. Development of antibodies ag ainst these proteins may be used to impair the normal feeding and consequen tly, the parasite would be no longer viable. (C) 1999 Elsevier Science B.V. All rights reserved.