Protease inhibitors have been reported rarely from the leech Hirudinaria manillensis. In this study, we purified a novel protease inhibitor (bdellin-HM-2) with anticoagulant properties from H. manillensis. With a molecular weight of 1.4x104, bdellin-HM-2 was also characterized with three intra-molecular disulfide bridges at the N-terminus and multiple HHXDD and HXDD motifs at the C-terminus. cDNA cloning revealed that the putative nucleotide-encoding protein of bdellin-HM-2 contained 132 amino acids and was encoded by a 399 bp open reading frame (ORF). Sequence alignment showed that bdellin-HM-2 shared similarity with the "non-classical" Kazal-type serine protease inhibitors, but had no inhibitory effect on trypsin, elastase, chymotrypsin, kallikrein, factor XIIa (FXIIa), factor XIa (FXIa), factor Xa (FXa), thrombin, or plasmin. Bdellin-HM-2 showed anticoagulant effects by prolonging the activated partial thromboplastin time (aPTT), indicating a role in enabling H. manillensis to obtain a blood meal from its host. Our results suggest that bdellin-HM-2 may play a crucial role in blood-sucking in this leech species and may be a potential candidate for the development of clinical anti-thrombotic drugs.
Keywords: Anti-thrombotic drugs; Anticoagulant; Bdellin-HM-2; Blood sucking; Hirudinaria manillensis; “Non-classical” Kazal inhibitors.