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Intersection of endocytic and exocytic systems in Toxoplasma gondii.

ABSTRACT: Host cytosolic proteins are endocytosed by Toxoplasma gondii and degraded in its lysosome-like compartment, the vacuolar compartment (VAC), but the dynamics and route of endocytic trafficking remain undefined. Conserved endocytic components and plant-like features suggest T. gondii endocytic trafficking involves transit through early and late endosome-like compartments (ELCs) and potentially the trans-Golgi network (TGN) as in plants. However, exocytic trafficking to regulated secretory organelles, micronemes and rhoptries, also proceeds through ELCs and requires classical endocytic components, including a dynamin-related protein, DrpB. Here, we show that host cytosolic proteins are endocytosed within 7 minutes post-invasion, trafficked through ELCs en route to the VAC, and degraded within 30?minutes. We could not definitively interpret if ingested protein is trafficked through the TGN. We also found that parasites ingest material from the host cytosol throughout the parasite cell cycle. Ingested host proteins colocalize with immature microneme proteins, proM2AP and proMIC5, in transit to the micronemes, but not with the immature rhoptry protein proRON4, indicating that endocytic trafficking of ingested protein intersects with exocytic trafficking of microneme proteins. Finally, we show that conditional expression of a DrpB dominant negative mutant increases T. gondii ingestion of host-derived proteins, suggesting that DrpB is not required for parasite endocytosis.

SUBMITTER: McGovern OL

PROVIDER: S-EPMC6787929 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Intersection of endocytic and exocytic systems in Toxoplasma gondii.

McGovern Olivia L OL Rivera-Cuevas Yolanda Y Kannan Geetha G Narwold Andrew J AJ Carruthers Vern B VB

Traffic (Copenhagen, Denmark) 20180325 5

Host cytosolic proteins are endocytosed by Toxoplasma gondii and degraded in its lysosome-like compartment, the vacuolar compartment (VAC), but the dynamics and route of endocytic trafficking remain undefined. Conserved endocytic components and plant-like features suggest T. gondii endocytic trafficking involves transit through early and late endosome-like compartments (ELCs) and potentially the trans-Golgi network (TGN) as in plants. However, exocytic trafficking to regulated secretory organell ...[more]

PMID: 29437275

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Project description:Toxoplasma gondii is a widely prevalent parasite of animals and humans that causes a broad spectrum of conditions ranging from asymptomatic or mild cold-like infections to abortion, severe ocular disease, encephalitis, and sometimes death. It is a member of the phylum Apicomplexa that also includes such significant human pathogens as Plasmodium spp. and Cryptosporidium spp. causing malaria and diarrheal disease, respectively. The toxoplasma cell has a multilayered pellicle: under the plasma membrane lies the inner membrane complex (IMC) comprised of flat membrane sacks supported by cortical microtubules and a meshwork of cytoskeletal filaments. The IMC acts as a mechanical barrier for membrane vesicles trafficking to and from the plasma membrane, necessitating the existence of dedicated cites for endo- and exocytosis where the IMC is interrupted. One such site is located at the apical end of the cell where the contents of the apical secretory organelles is exocytosed upon invasion. However, endocytosis in Toxoplasma and other apicomplexans is poorly understood, although conspicuous invaginations of the plasma membrane observed microscopically have been dubbed the micropore and postulated to be involved in endocytosis. We found that the endocytic markers including the subunits α and μ of the AP2 adaptor complex, dynamin-related protein C (DrpC), an Eps15 homology domain-containing protein, and the kelch-domain protein K13 localise to distinct persistent foci in the pellicle of Toxoplasma. Another type of persistent punctate structures found in the IMC are the enigmatic apical annuli whose function is completely unknown. We have discovered a new component of the annuli which is a putative LMBR1 family region protein embedded into the plasma membrane. Our experiments indicate that this protein – and annuli by extension – has a role in exocytosis. To better understand the molecular composition of these endocytic and exocytic structures and gain an insight into their function, we genetically fused them with a promiscuous bacterial biotin-ligase BirA* and used them as baits in proximity-dependent biotin identification experiments (BioID). We employed TMT10plex labelling and MS3-level tandem mass spectrometry with synchronous precursor selection (SPS-MS3) to achieve accurate quantification of multiple samples. Several hundred proteins have been identified and quantified in three biological replicates for every bait and the parental cell line control. Proteins significantly enriched in the BirA*-tagged cells relative to the control have been identified using linear modelling with LIMMA.

Dataset Information

Intersection of endocytic and exocytic systems in Toxoplasma gondii.

Publications

Intersection of endocytic and exocytic systems in Toxoplasma gondii.

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