title: Desialylation of lysosomal membrane glycoproteins by Trypanosoma cruzi: a role for the surface neuraminidase in facilitating parasite entry into the host cell cytoplasm.
abstract: Trypanosoma cruzi enters host cells via formation of an acidic vacuole which is subsequently disrupted, allowing the parasite access to the cytoplasm. We show that in an acid environment, release of the parasite surface neuraminidase is enhanced, and this release is likely mediated by a phosphatidylinositol-specific phospholipase C (PIPLC), since antibodies to a carbohydrate epitope (CRD) revealed in glycosylphosphatidylinositol (GPI)-anchored proteins after PIPLC cleavage remove the great majority of the soluble neuraminidase activity from culture supernatants. The neuraminidase is active at acidic pH, and is capable of desialylating known vacuolar constituents, i.e., lysosomal membrane glycoproteins. Parasite escape into the cytoplasm is significantly facilitated in terminal sialylation-defective mutant Lec 2 cells, and enzymatically desialylated membranes are more susceptible to lysis by a parasite hemolysin previously implicated in vacuole membrane rupture. These findings provide evidence that terminal sialylation on carbohydrate moieties contributes to maintaining lysosomal membrane integrity, and indicate a role for a protozoan-derived neuraminidase in facilitating parasite entry into host cells. These observations raise the possibility that other microbial neuraminidases may serve a similar function in acidic intracellular compartments.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510-8056.
authors.forename: B F
authors.initials: BF
authors.lastname: Hall
authors.forename: P
authors.initials: P
authors.lastname: Webster
authors.forename: A K
authors.initials: AK
authors.lastname: Ma
authors.forename: K A
authors.initials: KA
authors.lastname: Joiner
authors.forename: N W
authors.initials: NW
authors.lastname: Andrews
mesh_terms: D000818:Animals; D015703:Antigens, CD; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003593:Cytoplasm / Q000469:parasitology; D005455:Fluorescent Antibody Technique; D006863:Hydrogen-Ion Concentration; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000378:metabolism* / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008854:Microscopy, Electron; D019158:N-Acetylneuraminic Acid; D009439:Neuraminidase / Q000378:metabolism*; D012794:Sialic Acids / Q000378:metabolism*; D013379:Substrate Specificity; D014349:Trypanosoma cruzi / Q000201:enzymology* / Q000472:pathogenicity
chemical_list: D015703:Antigens, CD; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D012794:Sialic Acids; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid