Glycosylated compounds of parasitic protozoa

Parasitic protists belong to a range of deeply diverging eukaryotic taxa and are the cause of many important diseases in humans. These organisms are capable of surviving in multiple vertebrate and arthropod host environments and, in some cases, as free-living organisms. All parasitic protists express a range of glycoconjugates that form protective protein-rich or carbohydrate-rich surface coats. Protein-rich coats are typically found on developmental stages that inhabit non-hydrolytic niches, such as the bloodstream and non-acidified intracellular vacuoles. These coats are commonly dominated by a limited repertoire of antigenically diverse proteins that are commonly, but not always, glycosylphosphatidylinositol- (GPI-) anchored and modified with N- or O-glycans. Carbohydrate-rich coats are commonly found on developmental stages that dwell within hydrolytic environments, such as vertebrate and arthropod digestive tracts and lysosomal vacuoles. These coats are dominated by GPI-anchored glycoproteins that are heavily modified with N-glycans, O-glycans or phosphoglycans. Free GPI glycolipids (not attached to protein) can also be abundant or dominant components of these coats. Some parasitic protists can also form highly resistant cyst stages encased within polysaccharide-rich cell walls. Considerable progress has been made in defining the structures of the surface and intracellular glycans of the parasitic protists, their biosynthesis and the role that individual components play in parasite infectivity.