Unique Endomembrane Systems and Virulence in Pathogenic Protozoa

Abstract

Virulence in pathogenic protozoa is often tied to secretory processes such as the expression of adhesins on parasite surfaces or the secretion of proteases to assisted in tissue invasion and other proteins to avoid the immune system. This review is a broad overview of the endomembrane systems of pathogenic protozoa with a focus on Giardia, Trichomonas, Entamoeba, kinetoplastids, and apicomplexans. The focus is on unique features of these protozoa and how these features relate to virulence. In general, the basic elements of the endocytic and exocytic pathways are present in all protozoa. Some of these elements, especially the endosomal compartments, have been repurposed by the various species and quite often the repurposing is associated with virulence. The Apicomplexa exhibit the most unique endomembrane systems. This includes unique secretory organelles that play a central role in interactions between parasite and host and are involved in the invasion of host cells. Furthermore, as intracellular parasites, the apicomplexans extensively modify their host cells through the secretion of proteins and other material into the host cell. This includes a unique targeting motif for proteins destined for the host cell. Most notable among the apicomplexans is the malaria parasite, which extensively modifies and exports numerous proteins into the host erythrocyte. These modifications of the host erythrocyte include the formation of unique membranes and structures in the host erythrocyte cytoplasm and on the erythrocyte membrane. The transport of parasite proteins to the host erythrocyte involves several unique mechanisms and components, as well as the generation of compartments within the erythrocyte that participate in extraparasite trafficking.

Variant Surface Protein GP60 Contributes to Host Infectivity ofCryptosporidium parvum

“…Both the signal peptide and GPI anchor sequences are required for GP60 translocation, as depletion of the signal peptide resulted in GP60 accumulation in the cytosol, and depletion of the GPI anchor sequence changed the membrane location of the GP40 product to free in the parasitophorous vacuole and oocyst. This finding is expected because in eukaryotic cells the signal peptide is required for proper sorting of secretory proteins in the endoplasmic reticulum (29). Similarly, the GPI anchor is required for the sorting of GPI-anchored proteins from other secretory proteins in the trans-Golgi network for transport to the plasma membrane (26).…”

Knobs, Adhesion, and Severe Falciparum Malaria

“…These proteins are exported into the host erythrocyte via trafficking pathways with unique features [ 34 , 35 , 36 ]. For example, some exported parasite proteins have a unique targeting sequence called the Plasmodium export element (PEXEL), which is found in other apicomplexans and some stramenopiles [ 37 , 38 ]. Both KAHRP and PfEMP1 have PEXEL signals [ 39 ].…”

Fluorescent Nanoparticle Uptake by Myzocytosis and Endocytosis in Colpodella sp. ATCC 50594

“…The mechanisms of nutrient uptake by endocytosis and myzocytosis are unknown among the colpodellids. Although myzocytosis is thought to be the link between ancestral feeding mechanisms in colpodellids, gregarines and the pathogenic apicomplexans [ 19 ], very little information is available regarding the mechanisms of myzocytosis. In this study, we investigated nutrient uptake by Colpodella sp.…”