PROTOZOAN PARASITES Directing Traffic In

RESEARCH HIGHLIGHTS PROTOZOAN PARASITES Directing traffic in apicomplexan parasites NPG The secretory rhoptries and micronemes machinery components that are micronemes, could not form plaques on of apicomplexan parasites are crucial involved in anterograde transport and human fibroblast monolayers and failed for successful host infection. The in retrograde recycling. Therefore, to exit the host cell on experimental contents of these organelles are TgSORTLR was a good candidate for induction of egress. Following manual transported through the endoplasmic a protein-sorting receptor. release from host cells, these parasites reticulum (ER), Golgi and endosome TgSORTLR was also found to were impaired in gliding motility and system to their respective apical colocalize and interact with various in their ability to invade host cells. organelles, but how this directed rhoptry and microneme components Moreover, T. gondii-infected mice died transport is regulated was unknown. (ROP and MIC proteins, respectively), 9 days after infection when TgSORTLR Now, Tomavo and colleagues find that such as ROP1, ROP4, MIC1 and MIC5. was present in the parasites, but a Toxoplasma gondii homologue of In addition, a C-terminally truncated survived when the protein was depleted sortilin, TgSORTLR, is a cargo receptor TgSORTLR mislocalized to multiple (through an inducible knockout system) and chaperone that delivers cargo spots anterior and posterior to the at day 0 or even at day 5, by which time to rhoptries and micronemes for nucleus and was associated with the mice were showing symptoms of secretion. the mislocalization of MIC and ROP acute toxoplasmosis. Sortilin is a transmembrane cargo proteins throughout the cytoplasm. Thus, TgSORTLR is a cargo receptor receptor that functions in transport to The TgSORTLR amino-terminal lumenal and sorting protein that is required for the endolysosome system in yeast and domain was sufficient for interaction rhoptry and microneme biogenesis, mammals. The authors had previously with MIC and ROP proteins in cell trafficking components to these identified TgSORTLR in T. gondii and extracts but did not rescue cargo secretory organelles for regulated now sought to determine whether its localization when expressed in release. Precisely how this sortilin function in protein transport was TgSORTLR-deficient cells. Together, homologue recognizes its cargo proteins conserved. Using immunolabelling these results indicate that the and targets them to the correct organelle and colocalization approaches, they C-terminal cytoplasmic domain of remains to be determined. observed that TgSORTLR localized TgSORTLR contains sorting signals for Lucie Wootton to the Golgi, the trans-Golgi network trafficking of both TgSORTLR and its and endosomes, but not to the ER. cargo, whereas the lumenal domain is ORIGINAL RESEARCH PAPER Sloves, P.-J. et al. Furthermore, co-immunoprecipitation required for binding to its ROP and MIC Toxoplasma sortilin-like receptor regulates protein experiments showed that the TgSORTLR cargo proteins. transport and is essential for apical secretory carboxyl terminus interacted with TgSORTLR-deficient parasites organelle biogenesis and host infection. Cell Host Microbe 11, 515–527 (2012) homologues of cytosolic sorting contained no visible rhoptries or NATURE REVIEWS | MICROBIOLOGY VOLUME 10 | JULY 2012 © 2012 Macmillan Publishers Limited. All rights reserved.

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Essential Function of the Alveolin Network in the Subpellicular
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