A Cryptic Protease Activity fromTrypanosoma cruziRevealed by Preincubation with Kininogen at Low Temperatures

Abstract

Cysteine proteases have been identified in parasitic protozoa including the causative agent of Chagas’ diseaseTrypanosoma cruzi. T. cruzilysates subjected to substrate-containing SDS-polyacrylamide gel electrophoresis exhibit major bands of proteolytic activity in the 45-55 kDa molecular mass range (cruzipain activity). Paradoxically, addition of kininogen (a cystatin-like protease inhibitor) to the lysates before electrophoresis results in the appearance of additional bands of proteolytic activity in the 160-190 kDa molecular mass range. This inhibitor-activated protease activity depends upon the reaction conditions and exhibits novel properties. For example, a 24-48 hour preincubation at low temperature (−20°C optimum) greatly enhances the proteolytic activity. The results suggest that a metastable complex forms between kininogen and a cryptic 30 kDa cysteine protease fromT. cruziand that this complex participates in the activation of proteolytic activity.