Cathepsin Cs Are Key for the Intracellular Survival of the Protozoan Parasite, Toxoplasma gondii

Abstract

Cysteine proteases play key roles in apicomplexan invasion, organellar biogenesis, and intracellular survival. We have now characterized five genes encoding papain family cathepsins from Toxoplasma gondii, including three cathepsin Cs, one cathepsin B, and one cathepsin L. Unlike endopeptidases cathepsin B and L, T. gondii cathepsin Cs are exopeptidases and remove dipeptides from unblocked N-terminal substrates of proteins or peptides. TgCPC1 was the most highly expressed cathepsin mRNA in tachyzoites (by real-time PCR), but three cathepsins, TgCPC1, TgCPC2, and TgCPB, were undetectable in in vivo bradyzoites. The specific cathepsin C inhibitor, Gly-Phe-dimethylketone, selectively inhibited the TgCPCs activity, reducing parasite intracellular growth and proliferation. The targeted disruption of TgCPC1 does not affect the invasion and growth of tachyzoites as TgCPC2 is then up-regulated and may substitute for TgCPC1. TgCPC1 and TgCPC2 localize to constitutive secretory vesicles of tachyzoites, the dense granules. T. gondii cathepsin Cs are required for peptide degradation in the parasitophorous vacuole as the degradation of the marker protein, Escherichia coli ␤-lactamase, secreted into the parasitophorous vacuole of transgenic tachyzoites was completely inhibited by the cathepsin C inhibitor. Cathepsin C inhibitors also limited the in vivo infection of T. gondii in the chick embryo model of toxoplasmosis. Thus, cathepsin Cs are critical to T. gondii growth and differentiation, and their unique specificities could be exploited to develop novel chemotherapeutic agents.

Targeted Disruption of Toxoplasma gondii Serine Protease Inhibitor 1 Increases Bradyzoite Cyst Formation In Vitro and Parasite Tissue Burden in Mice

“…Targeted deletion of a gene family member in T. gondii can lead to upregulation of another member of the gene family (46). To determine whether deletion of TgPI1 resulted in compensatory upregulation of other T. gondii genes, including those encoding other serine protease inhibitors, we performed genome-wide expression profiling using a custom T. gondii Affymetrix microarray (Toxodb.org) (Fig.…”

Possible Pivotal Role of Latent Chronic T. gondii Infection in the Pathogenesis of Atherosclerosis

“…Cathepsin proteases act clasically as lysosomal hydrolases that digest endogenous and exogenous endocytosed polypeptides [706] . They function in microneme and rhoptry protein maturation, host cell invasion, replication, and nutrient acquisition [707,708] . Que et al [705] showed that the TgCatB, toxopain-1, was localized to rhoptries (secretory organelles required for parasite invasion into cells), and was critical for parasite invasion and rhoptry protein processing.…”

“…Cathepsins are critical to the parasite growth and differentiation [707] . T. gondii cathepsins were required for peptide degradation in the parasitophorous vacuole (PV), as the degradation of the marker protein, E. coli β-lactamase, secreted into the PV of transgenic tachyzoites was completely inhibited by the CatC inhibitor [707] .…”

“…T. gondii cathepsins were required for peptide degradation in the parasitophorous vacuole (PV), as the degradation of the marker protein, E. coli β-lactamase, secreted into the PV of transgenic tachyzoites was completely inhibited by the CatC inhibitor [707] . Tables 26 and 27 summarized classes and specific cathepsin-like proteases of T. gondii proteases, their function and localization, and the parasite stage expressions [708,712] .…”

Secretion of Polypeptide Crystals from Tetrahymena thermophila Secretory Organelles (Mucocysts) Depends on Processing by a Cysteine Cathepsin, Cth4p

“…Cathepsin C family members, including the Toxoplasma gondii enzyme most closely related to Cth4p, are comprised of 5 recognized domains: a signal peptide, an exclusion domain, a internal proregion, and finally a catalytic heavy and light chain (Fig. 12A) (48). In the comparatively well-studied mammalian cathepsin C, it is known that the first three domains are removed in a maturation process, to generate a catalytically active heavyϩlight chain (HL) species (49).…”