Purification, characterization, and cloning of a serine proteinase inhibitor from the ectoparasite Haematobia irritans irritans (Diptera: Muscidae)

Abstract

The fly Haematobia irritans irritans is one of the most important ectoparasites in cattle production, due to its ability to suck large amounts of blood. This report describes the purification and characterization of a serine proteinase inhibitor (HiTI) present in H. i. irritans head and thorax extracts. The HiTI purified by affinity chromatography on trypsin–Sepharose has a molecular mass of 7029 Da by MALDI-TOF mass spectrometry. HiTI inhibited bovine trypsin, human neutrophil elastase, and a trypsin-like enzyme purified from H. i. irritans abdomen with dissociation constants of 0.57, 1.30, and 0.20 nM, respectively. The HiTI partial amino acid sequence allowed its classification into the BPTI–Kunitz-type family. An HiTI cDNA fragment was cloned in the pGEMT vector using RT-PCR. The translated amino acid sequence of HiTI cDNA confirmed a unique Kunitz-type-domain protein. Our results suggest that HiTI could control some endogenous enzyme, e.g., the H. i. irritans trypsin-like protein. Index Descriptors and Abbreviations: Haematobia irritans irritans; Serine proteinase inhibitor; Kunitz-type inhibitor; HiTI, H. i. irritans trypsin inhibitor; bovine trypsin; Human plasmin; Human neutrophil elastase; Bovine thrombin; Human factor Xa; Human factor XIIa; Human plasma kallikrein; Subtilisin A; MALDI-TOF, matrix assisted laser desorption ionization time-of-flight; cDNA, complementary deoxyribonucleic acid; RT-PCR, reverse transcription polymerase chain reaction; TFA, trifluoroacetic acid