title: The protozoan parasite Toxoplasma gondii targets proteins to dense granules and the vacuolar space using both conserved and unusual mechanisms.
abstract: All known proteins that accumulate in the vacuolar space surrounding the obligate intracellular protozoan parasite Toxoplasma gondii are derived from parasite dense granules. To determine if constitutive secretory vesicles could also mediate delivery to the vacuolar space, T. gondii was stably transfected with soluble Escherichia coli alkaline phosphatase and E. coli beta-lactamase. Surprisingly, both foreign secretory reporters were delivered quantitatively into parasite dense granules and efficiently secreted into the vacuolar space. Addition of a glycosylphosphatidylinositol membrane anchor rerouted alkaline phosphatase to the parasite surface. Alkaline phosphatase fused to the transmembrane domain and cytoplasmic tail from the endogenous dense granule protein GRA4 localized to dense granules. The protein was secreted into a tuboreticular network in the vacuolar space, in a fashion dependent upon the cytoplasmic tail, but not upon a tyrosine-based motif within the tail. Alkaline phosphatase fused to the vesicular stomatitis virus G protein transmembrane domain and cytoplasmic tail localized primarily to the Golgi, although staining of dense granules and the intravacuolar network was also detected; truncating the cytoplasmic tail decreased Golgi staining and increased delivery to dense granules but blocked delivery to the intravacuolar network. Targeting of secreted proteins to T. gondii dense granules and the plasma membrane uses general mechanisms identified in higher eukaryotic cells but is simplified and exaggerated in scope, while targeting of secreted proteins beyond the boundaries of the parasite involves unusual sorting events.
authors.affiliation: Section of Infectious Diseases, Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8022, USA.
authors.forename: V
authors.initials: V
authors.lastname: Karsten
authors.forename: H
authors.initials: H
authors.lastname: Qi
authors.forename: C J
authors.initials: CJ
authors.lastname: Beckers
authors.forename: A
authors.initials: A
authors.lastname: Reddy
authors.forename: J F
authors.initials: JF
authors.lastname: Dubremetz
authors.forename: P
authors.initials: P
authors.lastname: Webster
authors.forename: K A
authors.initials: KA
authors.lastname: Joiner
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001665:Binding Sites; D020126:Brefeldin A; D002462:Cell Membrane / Q000378:metabolism; D002522:Chlorocebus aethiops; D003517:Cyclopentanes / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression; D017261:Glycosylphosphatidylinositols / Q000235:genetics / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D018942:Macrolides; D008562:Membrane Glycoproteins; D051379:Mice; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D013347:Subcellular Fractions; D014122:Toxoplasma / Q000378:metabolism*; D014617:Vacuoles; D014709:Vero Cells; D014759:Viral Envelope Proteins / Q000235:genetics / Q000378:metabolism; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D003517:Cyclopentanes; C028391:G protein, vesicular stomatitis virus; C079248:GRA4 protein, Toxoplasma gondii; D017261:Glycosylphosphatidylinositols; D018942:Macrolides; D008562:Membrane Glycoproteins; D011500:Protein Synthesis Inhibitors; D015800:Protozoan Proteins; D014759:Viral Envelope Proteins; D020126:Brefeldin A; D000469:Alkaline Phosphatase; D001618:beta-Lactamases