A Novel Protease and Digestive Compartment in the Pathogenic Protozoan Toxoplasma gondii

FABIOLA PARUSSINI; ISABELLE COPPENS; VERN B. CARRUTHERS

San Diego

Congreso; The American Society for Cell Biology 46th Annual Meeting; 2006

The American Society for Cell Biology

While navigating the regulatedsecretory pathway, proteins are often converted from a precursor to a maturepolypeptide. Although studies in higher eukaryotes have indicated thatproteolytic maturation can activate the substrate protein, aid in traffickingthrough the pathway, or facilitate dense packing within nascent secretorygranules, much less is known about this phenomenon in lower eukaryotes. Toxoplasmagondii is an obligate intracellular eukaryotic pathogen that relies on cellhost invasion as a major survival strategy. Invasion related proteins areproteolytically processed during their transport to specialized secretoryorganelles (micronemes and rhoptries) that are sequentially discharged duringcell entry. Using general and specific inhibitors we have found evidence that TgCPL, Toxoplasmagondii cathepsin L-like enzyme, is involved in the proteolytic maturationof multiple microneme adhesin complexes. In the tachyzoite invasion form, TgCPLis located in a novel, photon lucent structure visible by phase contrastmicroscopy and positioned in the apical region between the Golgi and apicalsecretory organelles. Serial sections of the same parasite shown by electronmicroscopy indicate that TgCPL is associated to the limiting membrane andinternal vesicles of a large multi-vesiculated compartment, which is also occupiedby a proton-pump, the Toxoplasma gondii vacuolar pyrophosphatase TgVP1.During intracellular replication the compartment is highly dynamic and isfragmented in multiple vesicles. We speculate that TgCPL is a multifunctionalenzyme involved in both the proteolytic maturation of microneme proteincomplexes and the degradation of endogenous and exogenous substrates within theendocytic pathway.