Transmembrane Domain Modulates Sorting of Membrane Proteins in Toxoplasma gondii

Karsten, Verena; Hegde, Ramanujan S.; Sinai, Anthony P.; Yang, Mei; Joiner, Keith A.

doi:10.1074/jbc.m400480200

Cited by 31 publications

(23 citation statements)

References 43 publications

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“…For example, the transmembrane domain of the plant vacuolar receptor BP80 (proaleurain-binding protein of 80 kDa) is sufficient for targeting a chimeric protein to a lytic compartment in plants (58). GRA4, a dense granule (a secretory compartment) protein of T. gondii also requires a transmembrane domain for correct localization (59). In contrast, the directional transport of EBA-175 to the micronemes is independent of its membrane association.…”

Section: Discussionmentioning

confidence: 99%

A Conserved Region in the EBL Proteins Is Implicated in Microneme Targeting of the Malaria ParasitePlasmodium falciparum

et al. 2006

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The proliferation of the malaria parasite Plasmodium falciparum within the human host is dependent upon invasion of erythrocytes. This process is accomplished by the merozoite, a highly specialized form of the parasite. Secretory organelles including micronemes and rhoptries play a pivotal role in the invasion process by storing and releasing parasite proteins. The mechanism of protein sorting to these compartments is unclear. Using a transgenic approach we show that trafficking of the most abundant micronemal proteins (members of the EBL-family: EBA-175, EBA-140/BAEBL, and EBA-181/JSEBL) is independent of their cytoplasmic and transmembrane domains, respectively. To identify the minimal sequence requirements for microneme trafficking, we generated parasites expressing EBA-GFP chimeric proteins and analyzed their distribution within the infected erythrocyte. This revealed that: (i) a conserved cysteine-rich region in the ectodomain is necessary for protein trafficking to the micronemes and (ii) correct sorting is dependent on accurate timing of expression.Plasmodium falciparum is the causative agent of the most severe form of human malaria. Increasing global prevalence of malaria is reported, and it is estimated that mortality reaches 1-2 million per year, with the biggest impact on young African children (1). The invasion, host cell modification and subsequent destruction of erythrocytes by the obligatory intracellular parasite are responsible for the pathobiology in the human host. The invasion process is initiated by merozoites, polarorganized, ϳ1.8 m, slightly elongated invasive cells (2, 3). Secretory organelles including the micronemes and rhoptries (4) store and secrete proteins that enable the parasite to (i) adhere to surface receptors of the host cell, (ii) invade the new host cell, and (iii) establish itself within the parasitophorous vacuole (5). Because of compartmentalization, this small protozoan parasite relies on a sophisticated secretory system that delivers proteins to multiple subcellular destinations (6 -11).Trafficking is initiated by classical N-terminal signal sequences that direct proteins across the endoplasmic reticulum (ER) into the secretory pathway (12). In the Golgi and trans-Golgi network (TGN) the proteins are routed either to constitutive or regulated secretory pathways (13). Once the proteins reach the Golgi exit face, they are embedded into transport vesicles according to sequence information or by an acquired label and brought to their final destinations (14). Proteins entering the regulated pathways are sorted to secretory compartments and are released upon a stimulus (15). One intriguing question concerns the nature of the signal(s) necessary and sufficient for post-Golgi protein sorting to the predetermined destinations. In mammalian cells the transport of transmembrane proteins to endosomes and lysosomes is most commonly mediated by distinct cytoplasmic-sorting motifs (16,17). This has also been shown in the protozoan Toxoplasma gondii, a Plasmodium-related parasite. T...

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Section: Discussionmentioning

confidence: 99%

A Conserved Region in the EBL Proteins Is Implicated in Microneme Targeting of the Malaria ParasitePlasmodium falciparum

et al. 2006

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“…Immunofluorescence assays were performed as described previously (Karsten et al ., 2004), except that the permeabilization step with 0.3% Triton X-100 in PBS was omitted for samples fixed with methanol. Coverslips were mounted using ProLong antifade mounting solution (Invitrogen).…”

Section: Methodsmentioning

confidence: 99%

Toxoplasma gondiisalvages sphingolipids from the host Golgi through the rerouting of selected Rab vesicles to the parasitophorous vacuole

Romano

Sonda

Bergbower

et al. 2013

MBoC

105

147

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“…Typically containing signal peptides, GRA proteins are first synthesized in the secretory pathway and then targeted to the dense granules, the default targeting pathway for T. gondii secretory proteins (23). Protein storage within the cores of the dense granules is believed to be achieved by the formation of high-molecular-weight GRA complexes, which explains how these proteins are able to mask their transmem-brane domains and thus be stored internally in the organelle (6).…”

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Intervacuolar Transport and Unique Topology of GRA14, a Novel Dense Granule Protein inToxoplasma gondii

et al. 2008

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Toxoplasma gondii is an obligate intracellular parasite that resides in the cytoplasm of its host in a unique membrane-bound vacuole known as the parasitophorous vacuole (PV). The membrane surrounding the parasite is remodeled by the dense granules, secretory organelles that release an array of proteins into the vacuole and to the PV membrane (PVM). Only a small portion of the protein constituents of the dense granules have been identified, and little is known regarding their roles in infection or how they are trafficked within the infected host cell. In this report, we identify a novel secreted dense granule protein, GRA14, and show that it is targeted to membranous structures within the vacuole known as the intravacuolar network and to the vacuolar membrane surrounding the parasite. We disrupted GRA14 and exploited the knockout strain to show that GRA14 can be transferred between vacuoles in a coinfection experiment with wild-type parasites. We also show that GRA14 has an unexpected topology in the PVM with its C terminus facing the host cytoplasm and its N terminus facing the vacuolar lumen. These findings have important implications both for the trafficking of GRA proteins to their ultimate destinations and for expectations of functional domains of GRA proteins at the host-parasite interface.Capable of infecting essentially any warm-blooded vertebrate, Toxoplasma gondii is one of the most successful pathogens on the planet (20, 39). Toxoplasma infects nearly onethird of the human population and causes potentially fatal disease in immunocompromised individuals and congenitally infected neonates (20). This protozoan parasite also causes ocular disease in immunocompetent individuals who are either congenitally or postnatally infected (46). As an obligate intracellular parasite, Toxoplasma enters the host cell into a nonfusogenic vacuole (the parasitophorous vacuole [PV]), in which the parasite replicates in the cytoplasm of its host. The PV membrane (PVM) is porous to small molecules (less than 1,300 Da) but otherwise serves as a boundary between the host and parasite during its intracellular survival (36).Toxoplasma invasion is mediated by a trio of specialized secretory organelles, named the micronemes, rhoptries, and dense granules, which contribute to the parasite's ability to initiate and sustain infection within its host. The first proteins secreted are from the micronemes, which release molecular adhesins that interact with the parasite's actin-myosin motor to provide the driving force for invasion (24). The rhoptries are then released and help to establish the nascent PV and modulate host cell processes (4). Lastly, proteins from the dense granules that are implicated in the remodeling and maintenance of the PV for intracellular survival are secreted (29).The precise role of dense granule proteins (GRAs) in the T. gondii life cycle is still largely unknown. To date, two groups of GRA proteins have been identified. The first group contains proteins that lack homology to organisms other than closely relat...

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Transmembrane Domain Modulates Sorting of Membrane Proteins in Toxoplasma gondii

Cited by 31 publications

References 43 publications

A Conserved Region in the EBL Proteins Is Implicated in Microneme Targeting of the Malaria ParasitePlasmodium falciparum

A Conserved Region in the EBL Proteins Is Implicated in Microneme Targeting of the Malaria ParasitePlasmodium falciparum

Toxoplasma gondiisalvages sphingolipids from the host Golgi through the rerouting of selected Rab vesicles to the parasitophorous vacuole

Intervacuolar Transport and Unique Topology of GRA14, a Novel Dense Granule Protein inToxoplasma gondii

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