An unexpected inhibitory activity of Kunitz-type serine proteinase inhibitor derived from Boophilus microplus trypsin inhibitor on cathepsin L

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. microplus 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 (Ki 3.3 and 1.0 nM) and human plasma kallikrein (Ki 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.