Cathepsin L occupies a vacuolar compartment and is a protein maturase within the endo/exocytic system of Toxoplasma gondii

Abstract

SummaryRegulated exocytosis allows the timely delivery of proteins and other macromolecules precisely when they are needed to fulfil their functions. The intracellular parasite Toxoplasma gondii has one of the most extensive regulated exocytic systems among all unicellular organisms, yet the basis of protein trafficking and proteolytic modification in this system is poorly understood. We demonstrate that a parasite cathepsin protease, TgCPL, occupies a newly recognized vacuolar compartment (VAC) that undergoes dynamic fragmentation during T. gondii replication. We also provide evidence that within the VAC or late endosome this protease mediates the proteolytic maturation of proproteins targeted to micronemes, regulated secretory organelles that deliver adhesive proteins to the parasite surface during cell invasion. Our findings suggest that processing of microneme precursors occurs within intermediate endocytic compartments within the exocytic system, indicating an extensive convergence of the endocytic and exocytic pathways in this human parasite.

Characterization of the Chloroquine Resistance Transporter Homologue in Toxoplasma gondii

“…In this study, we characterized the CRT homologue from the model apicomplexan T. gondii, revealing that TgCRT localizes to the recently described VAC compartment (11). The VAC is a proteolytic compartment that houses cathepsin-like cysteine proteases, such as TgCPL and TgCPB (11,39).…”

“…The vesicular pattern of TgCRT labeling resembled that of the fragmented VAC compartment described in intracellular parasites (11). We therefore colabeled TgCRT-HA 3 -expressing parasites with antibodies against TgCPL, a marker for the VAC.…”

“…We demonstrated that, in intracellular parasites, TgCRT localized to highly dynamic vesicles that overlapped the markers for a lysosome-like vacuolar compartment called the VAC (11). In extracellular parasites, TgCRT localized to one or a few larger, vacuole-like compartments that also overlapped the VAC markers.…”

“…2E, arrowheads). We next colabeled TgCRT-HA 3 with antibodies against vacuolar pyrophosphatase-1 (TgVP1), a marker for the late endosomes in intracellular parasites (11,28). We observed essentially no overlap between these structures (Fig.…”

“…The lytic cycle of T. gondii alternates between intracellular dividing cells and motile extracellular stages. The VAC is highly dynamic in intracellular tachyzoites (11). During most stages of the parasite lytic cycle, the VAC is fragmented into multiple smaller vesicular structures, but it is seen as one or more larger vacuolar structures in extracellular parasites.…”