The obligate intracellular parasite Toxoplasma can infect all nucleated cells and resides within a parasitophorous vacuole where it must salvage nutrients from host cells. Endocytosis is therefore an important mechanism for nutrient acquisition and represents a logical and potential target for antiparasitic therapy and drug delivery. Surprisingly, endocytosis is relatively uncharacterized in Toxoplasma, or in the related malarial parasite Plasmodium. This proposal aims to provide the groundwork for understanding the endocytic pathway in T. gondii. First, the endocytic cascade will be mapped by pulse chase internalization studies of fluid-phase tracers and biotinylated surface proteins using confocal or cytochemical EM. Second, the mechanism controlling the endocytic machinery will be examined by kinetic studies of endocytosis in intact and permeabilized cells, by pharmacological manipulation of cytoskeletal and signal transduction components. Third, the universal tyrosine-based internalization signal will be evaluated in T. gondii by the use of foreign endocytic reporters. These reporters contain an E. coli beta-lactamase ectodomain and the transmembrane and cytoplasmic tail of the LDL receptor. Introduction of well-defined mutation in the internalization signal of the LDL-R cytoplasmic tail will be used to probe the endocytic machinery of T. gondii without the requirement to identify individual components in the pathway. These experiments will be an important step for future toxin delivery or targeted-disruption of the endocytic pathway in apicomplexan parasites.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Postdoctoral Individual National Research Service Award (F32)
Project #
5F32AI010044-02
Application #
6124329
Study Section
Special Emphasis Panel (ZRG5-TMP (01))
Program Officer
Fairfield, Alexandra
Project Start
1999-11-30
Project End
Budget Start
1999-11-30
Budget End
2000-11-29
Support Year
2
Fiscal Year
2000
Total Cost
$38,368
Indirect Cost
Name
Yale University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
082359691
City
New Haven
State
CT
Country
United States
Zip Code
06520
Ngo, Huan M; Yang, Mei; Joiner, Keith A (2004) Are rhoptries in Apicomplexan parasites secretory granules or secretory lysosomal granules? Mol Microbiol 52:1531-41
Ngo, Huan M; Yang, Mei; Paprotka, Kerstin et al. (2003) AP-1 in Toxoplasma gondii mediates biogenesis of the rhoptry secretory organelle from a post-Golgi compartment. J Biol Chem 278:5343-52
Nakaar, Valerian; Ngo, Huan M; Aaronson, Emily P et al. (2003) Pleiotropic effect due to targeted depletion of secretory rhoptry protein ROP2 in Toxoplasma gondii. J Cell Sci 116:2311-20
Robibaro, B; Hoppe, H C; Yang, M et al. (2001) Endocytosis in different lifestyles of protozoan parasitism: role in nutrient uptake with special reference to Toxoplasma gondii. Int J Parasitol 31:1343-53
Liendo, A; Stedman, T T; Ngo, H M et al. (2001) Toxoplasma gondii ADP-ribosylation factor 1 mediates enhanced release of constitutively secreted dense granule proteins. J Biol Chem 276:18272-81
Ngo, H M; Hoppe, H C; Joiner, K A (2000) Differential sorting and post-secretory targeting of proteins in parasitic invasion. Trends Cell Biol 10:67-72
Hoppe, H C; Ngo, H M; Yang, M et al. (2000) Targeting to rhoptry organelles of Toxoplasma gondii involves evolutionarily conserved mechanisms. Nat Cell Biol 2:449-56