The first serine protease inhibitor from Lasiodora sp. (Araneae: Theraphosidae) hemocytes

► An extract from Lasiodora sp. hemocytes inhibited different serine proteases. ► Hemocyte extract inhibited growth of Bacillus subtilis and Enterococcus faecalis. ► An elastase inhibitor (EILaH) with 8274Da was purified from hemocytes. ► EILaH (Ki: 0.32nM) amino terminal sequence is LPC(PF)PYQQELTC. ► EILaH showed bacteriostatic activity against E. faecalis. This work reports, for the first time, the purification, characterization and antibacterial activity of an elastase inhibitor from Lasiodora sp. hemocytes (EILaH). The hemocyte extract inhibited chymotrypsin (22%), trypsin (44%), tissue plasminogen activator (52%), urokinase (58%) and human neutrophil elastase (99%). EILaH was purified by Trypsin-Sepharose column and RP-HPLC. SDS-PAGE of EILaH revealed a molecular mass of 8kDa and MALDI-TOF mass spectrometry revealed a single molecular mass of 8274Da. The amino terminal sequence determined was LPC(PF)PYQQELTC. The dissociation constant (Ki) for human neutrophil elastase was 0.32nM. Hemocyte extract exerted antibacterial effect on Bacillus subtilis and Enterococcus faecalis, while EILaH was only active against E. faecalis. Currently, Lasiodora sp. is undergoing a systematic review and this study contributes to molecular characterization of the genus. In addition, the results suggest that serine protease inhibitors expressed in Lasiodora sp. hemocytes may be involved in the defense against bacterial infection.