Several BPTI-Kunitz-type serine proteinase inhibitors were described in tick Boophilus microplus and Rhipicephalus sanguineus species. In this work, we present a synthetic gene based on two tick BPTI-Kunitz-type serine proteinase inhibitors, the first domain of B. micro-plus trypsin inhibitor-A (BmTI-A) and the carrapatin, the inhibitors were named BmTIsint and BmTIsint Mut. Our present results showed that BmTIsint and BmTIsint Mut inhibited trypsin (K-i 3.3 and 1.0 nM) and human plasma kallikrein (K-i 16.5 and 35 nM), but in contrast to BmTI-A, the inhibitors did not inhibit human neutrophil elastase. BmTIsint was able to produce immunological response in mice but not in bovines. In addition, it is the first description of a BPTI-Kunitz-type inhibitor as a cysteine proteinase inhibitor, BmTIsint apparent dissociation constant (Ki) for cathepsin L was 108 nM. Our findings open the possibility up to obtain new molecules as potent serine or cysteine proteinase inhibitors using BmTIsint as a model. (c) 2006 Elsevier Inc. All rights reserved.