Secretory organelle trafficking in Toxoplasma gondii: A long story for a short travel (original) (raw)
Related papers
Journal of Biological Chemistry, 2003
Toxoplasma gondii relies on protein secretion from specialized organelles for invasion of host cells and establishment of a parasitophorous vacuole. We identify T. gondii Rab6 as a regulator of protein transport between post-Golgi dense granule organelles and the Golgi. Toxoplasma Rab6 was localized to cisternal rims of the late Golgi and trans-Golgi network, associated transport vesicles, and microdomains of dense granule and endosomal membranes. Overexpression of wildtype Rab6 or GTP-activated Rab6(Q70L) rerouted soluble dense granule secretory proteins to the Golgi and endoplasmic reticulum and augmented the effect of brefeldin A on Golgi resorption to the endoplasmic reticulum. Parasites expressing a nucleotide-free (Rab6(N124I)) or a GDP-bound (Rab6(T25N)) mutant accumulated dense granule proteins in the Golgi and associated transport vesicles and displayed reduced secretion of GRA4 and a delay in glycosylation of GRA2. Activated Rab6 on Golgi membranes colocalized with centrin during mitosis, and parasite clones expressing Rab6 mutants displayed a partial shift in cytokinesis from endodyogeny (formation of two daughter cells) to endopolygeny (multiple daughter cells). We propose that Toxoplasma Rab6 regulates retrograde transport from post-Golgi secretory granules to the parasite Golgi.
Scientific reports, 2016
Accurate sorting of proteins to the three types of parasite-specific secretory organelles namely rhoptry, microneme and dense granule in Toxoplasma gondii is crucial for successful host cell invasion by this obligate intracellular parasite. Despite its tiny body architecture and limited trafficking machinery, T. gondii relies heavily on transport of vesicles containing proteins, lipids and important virulence-like factors that are delivered to these secretory organelles. However, our understanding on how trafficking of vesicles operates in the parasite is still limited. Here, we show that the T. gondii vacuolar protein sorting 9 (TgVps9), has guanine nucleotide exchange factor (GEF) activity towards Rab5a and is crucial for sorting of proteins destined to secretory organelles. Our results illuminate features of TgVps9 protein as a key trafficking facilitator that regulates protein maturation, secretory organelle formation and secretion, thereby ensuring a primary role in host infect...
Traffic, 2008
Toxoplasma gondii is the formation of a membranebound compartment within which the parasite proliferates. This process relies on a set of secretory organelles that discharge their contents into the host cell upon invasion. Among these organelles, the dense granules are specialized in the export of transmembrane (TM) GRA proteins, which are major components of the mature parasitophorous vacuole (PV) membrane. How eukaryotic pathogens export and sort membrane-bound proteins destined for the host cell is still poorly understood at the mechanistic level. In this study, we show that soluble trafficking of the PV-targeted GRA5 TM protein is parasite specific: when expressed in mammalian cells, GRA5 is targeted to the plasma membrane and behaves as an integral membrane protein with a type I toplogy. We also demonstrate the dual role of the GRA5 N-terminal ectodomain, which is sufficient to prevent membrane integration within the parasite and is essential for both sorting and post-secretory membrane insertion into the vacuolar membrane. These results contrast with the general rule that states that information contained within the cytoplasmic tail and/or the TM domain of integral membrane proteins dictates their cellular localization. They also highlight the diversity of sorting mechanisms that leads to the specialization of secretory processes uniquely adapted to intracellular parasitism.
International Journal for Parasitology, 2010
How eukaryotic pathogens export and sort membrane-bound proteins destined for host-cell compartments is still poorly understood. The dense granules of the intracellular protozoan Toxoplasma gondii constitute an unusual secretory pathway that allows soluble export of the GRA proteins which become membrane-associated within the parasite replicative vacuole. This process relies on both the segregation of the proteins routed to the dense granules from those destined to the parasite plasma membrane and on the sorting of the secreted GRA proteins to their proper final membranous system. Here, we provide evidence that the soluble trafficking of GRA6 to the dense granules relies on the N-terminal domain of the protein, which is sufficient to prevent GRA6 targeting to the parasite plasma membrane. We also show that the GRA6 N-terminal domain, possibly by interacting with negatively charged lipids, is fundamental for proper GRA6 association with the vacuolar membranous network of nanotubes. These results support our emerging model: sorting of transmembrane GRA proteins to the host cell vacuole is mainly driven by the dual role of their N-terminal hydrophilic domain and is compartmentally regulated.
PLoS pathogens, 2017
Toxoplasma gondii possesses a highly polarized secretory system, which efficiently assembles de novo micronemes and rhoptries during parasite replication. These apical secretory organelles release their contents into host cells promoting parasite invasion and survival. Using a CreLox-based inducible knock-out strategy and the ddFKBP over-expression system, we unraveled novel functions of the clathrin adaptor complex TgAP1. First, our data indicate that AP1 in T. gondii likely functions as a conserved heterotetrameric complex composed of the four subunits γ, β, μ1, σ1 and interacts with known regulators of clathrin-mediated vesicular budding such as the unique ENTH-domain containing protein, which we named Epsin-like protein (TgEpsL). Disruption of the μ1 subunit resulted in the mis-sorting of microneme proteins at the level of the Trans-Golgi-Network (TGN). Furthermore, we demonstrated that TgAP1 regulates rhoptry biogenesis by activating rhoptry protein exit from the TGN, but also ...
PLoS pathogens, 2005
Apicomplexan parasites, including Toxoplasma gondii and Plasmodium sp., are obligate intracellular protozoa. They enter into a host cell by attaching to and then creating an invagination in the host cell plasma membrane. Contact between parasite and host plasma membranes occurs in the form of a ring-shaped moving junction that begins at the anterior end of the parasite and then migrates posteriorly. The resulting invagination of host plasma membrane creates a parasitophorous vacuole that completely envelops the now intracellular parasite. At the start of this process, apical membrane antigen 1 (AMA1) is released onto the parasite surface from specialized secretory organelles called micronemes. The T. gondii version of this protein, TgAMA1, has been shown to be essential for invasion but its exact role has not previously been determined. We identify here a trio of proteins that associate with TgAMA1, at least one of which associates with TgAMA1 at the moving junction. Surprisingly, these new proteins derive not from micronemes, but from the anterior secretory organelles known as rhoptries and specifically, for at least two, from the neck portion of these club-shaped structures. Homologues for these AMA1-associated proteins are found throughout the Apicomplexa strongly suggesting that this moving junction apparatus is a conserved feature of this important class of parasites. Differences between the contributing proteins in different species may, in part, be the result of selective pressure from the different niches occupied by these parasites. Citation: Alexander DL, Mital J, Ward GE, Bradley P, Boothroyd JC (2005) Identification of the moving junction complex of Toxoplasma gondii: A collaboration between distinct secretory organelles. PLoS Pathog 1(2): e17.
Secretory traffic in the eukaryotic parasite Toxoplasma gondii: less is more
The Journal of Cell Biology, 2002
Name a single-celled eukaryote that boasts a small genome size, is easily cultivated in haploid form, for which a wide variety of molecular genetic tools are available, and that exhibits a simple, polarized secretory apparatus with a well-defined endoplasmic reticulum and Golgi that can serve as a model for understanding secretion. Got it? Now name a cell with all these attributes that contains at least a dozen distinct and morphologically well-defined intracellular organelles, including three distinct types of secretory vesicles and two endosymbiotic organelles. Not so sure anymore?
Targeting the Secretory Pathway ofToxoplasma gondii
Methods, 1997
dogenous proteins can be used for these studies, Little is known about the extent of conservation in the although they have to be ''tagged'' by the introducorganization of the secretory pathway in organisms as differtion of a novel antibody epitope. Alternatively, enent as prokaryotes, eukaryotes, and humans. The protozoan tirely foreign proteins, which may or may not be parasite Toxoplasma gondii allows easy genetic manipuladevoid of any intrinsic targetting information, have tions, and numerous vectors for selection of transgenic paraalso been used successfully.
PLoS Pathogens, 2013
The basic organisation of the endomembrane system is conserved in all eukaryotes and comparative genome analyses provides compelling evidence that the endomembrane system of the last common eukaryotic ancestor (LCEA) is complex with many genes required for regulated traffic being present. Although apicomplexan parasites, causative agents of severe human and animal diseases, appear to have only a basic set of trafficking factors such as Rab-GTPases, they evolved unique secretory organelles (micronemes, rhoptries and dense granules) that are sequentially secreted during invasion of the host cell. In order to define the secretory pathway of apicomplexans, we performed an overexpression screen of Rabs in Toxoplasma gondii and identified Rab5A and Rab5C as important regulators of traffic to micronemes and rhoptries. Intriguingly, we found that not all microneme proteins traffic depends on functional Rab5A and Rab5C, indicating the existence of redundant microneme targeting pathways. Using two-colour super-resolution stimulated emission depletion (STED) we verified distinct localisations of independent microneme proteins and demonstrate that micronemal organelles are organised in distinct subsets or subcompartments. Our results suggest that apicomplexan parasites modify classical regulators of the endocytic system to carryout essential parasite-specific roles in the biogenesis of their unique secretory organelles.
Cellular Microbiology, 2000
In mammalian cells and yeasts, amino acid motifs in the cytoplasmic tails of transmembrane proteins play a prominent role in protein targeting in the early secretory pathway by mediating localization to or rapid export from the endoplasmic reticulum (ER). However, early sorting events are poorly characterized in protozoan parasites. Here, we show that a C-terminal QKTT sequence mediates the ER localization of chimeric reporter constructs consisting of bacterial alkaline phosphatase (BAP) fused to the transmembrane domain (TMD) and truncated cytoplasmic tail of the human low-density lipoprotein receptor (LDL) receptor or of murine lysosomeassociated membrane protein (lamp-1) in Toxoplasma gondii. The cytoplasmic tail of human TGN46 also determines ER localization of BAP chimeras in the parasite, but this can be overcome by the addition at the C-terminus of the tail of an acidic patch, which functions as an ER export signal in conjunction with an upstream tyrosine motif. These results suggest that COPI-dependent ER retrieval and COPII-dependent export mechanisms mediated by KKXX and DXE motifs of mammalian cells are generally conserved in T. gondii. In contrast, the failure of the QKTT motif and TGN46 cytoplasmic tail to induce steady-state ER localization of vesicular stomatitis virus glycoprotein (VSVG) chimeras in HeLa and NRK cells indicates that significant differences in early secretory trafficking also exist.