Labelling of four distinct trophozoite falcipains of Plasmodium falciparum by a cystatin-derived probe
Abstract
Trophozoite cysteine protease (TCP) activity, isolated from Plasmodium falciparum soluble 100 000 g extracts, displayed native falcipain-1 kinetic parameters towards peptidyl substrates. The labelling of either isolated TCP or soluble 100 000 g extracts by a cystatin-derived probe (biotinyl-Leu-Val-Gly-CHN 2) revealed a single band of ca. 30 kDa by SDS-PAGE, which was resolved into four spots displaying isoelectric points (pI) from 4.7 to 5.3 after two-dimensional separation. The molecular mass and pI correspond to those of falcipain-3, falcipain-2, fal-cipain-29 and falcipain-1, respectively. The two central spots were identified by matrix-assisted laser desorption/ ionisation time-of-flight mass spectrometry as falcipain-2 and falcipain-29. This activity-based probe represents a potential tool for profiling active falcipains in parasites.