Evidence for the existence of a proteasome in Toxoplasma gondii: Intracellular localization and specific peptidase activities

Abstract

The proteasome is a large intracellular protein complex whose main function is proteolytic removal of damaged proteins. It has recently been shown that the proteasome has a crucial role in the pathogenesis of protozoan parasites. We attempted to characterize the proteasome of T. gondii (RH strain). In immunoblot experiments, we showed that MCP231 monoclonal antibody, directed against the human 20S proteasome, labelled homologous proteins in T. gondii with a pattern similar to that observed in mammalian cells. The study of in vitro proteolytic activities showed that chymotrypsin-like activity (the only activity obtained with archaebacteria) was present in Toxoplasma, with Km, and specific activity values close to those observed with eukaryotic cells, Immunofluorescence studies showed that the Toxoplasma proteasome predominated in the cytosol.