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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ERD2 gene product in mammalian cells and yeast is a receptor required for protein retention in the endoplasmic reticulum (ER); immunolocalization studies indicate that the protein is concentrated in the cis Golgi. We have identified a homologue of ERD2 in the malaria parasite, Plasmodium falciparum (PfERD2). The deduced protein sequence is 42% identical to mammalian and yeast homologues and bears striking homology in its proposed tertiary structure. PfERD2 is tightly confined to a single focus of staining in the perinuclear region as seen by indirect immunofluorescence. This is redistributed by brefeldin A (BFA) to a diffuse pattern similar to that of parasite BiP, a marker for the ER; removal of the drug results in recovery of the single focus, consistent with the localization of PfERD2 to the parasite Golgi and its participation in a retrograde transport pathway to the ER. Sphingomyelin synthesis is a second resident activity of the cis Golgi whose organization is sensitive to BFA in mammalian cells. Within the parasite it again localizes to a perinuclear region but does not reorganize upon BFA treatment. The results strongly suggest that these two activities are in distinct compartments of the Golgi in the malaria parasite.
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PMID:Identification and localization of ERD2 in the malaria parasite Plasmodium falciparum: separation from sites of sphingomyelin synthesis and implications for organization of the Golgi. 822 85

The rab6 gene product in mammalian cells and yeast is localized to and regulates protein transport in the medial and trans Golgi cisternae, as well as the trans Golgi network. We have identified a homologue in the malaria parasite Plasmodium falciparum which displays a rab-like sequence that is 62.4% identical to mammalian rab6. In addition the parasite gene (Pfrab6 gene) contains an N-terminal hydrophobic domain, unique to P. falciparum. Antibodies developed to Pfrab6 localize protein in 4-7 well-resolved sites in a ring-stage parasite, as detected by high resolution fluorescence microscopy. This suggests that there are multiple, distinct foci of medial/trans Golgi membranes in a ring. ERD2 is a cis Golgi marker in mammalian cells. The plasmodial homologue of ERD2 (PfERD2) is concentrated in a single perinuclear region in a ring-stage parasite. This site is distinct from the Pfrab6 membranes, indicating that early and late Golgi markers can be segregated in P. falciparum. Mammalian cells contain a single Golgi complex where cis medial and trans markers are tightly stacked in closely apposed cisternae. In P. falciparum-rings however, rab6-associated membranes are not invariably 'stacked' with an ERD2 structure. In immunoelectron microscopy studies, both the PfERD2- and Pfrab6-associated membranes appear tubulovesicular in nature, devoid of cisternal morphology. Hence the Golgi of ring stage parasites may comprise of multiple, 'unstacked' tubulovesicular clusters, suggesting a primitive organization of the organelle in Plasmodia.
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PMID:Identification and localization of rab6, separation of rab6 from ERD2 and implications for an 'unstacked' Golgi, in Plasmodium falciparum. 901 Aug 46

Toxoplasma gondii and its apicomplexan relatives (such as Plasmodium falciparum, which causes malaria) are obligate intracellular parasites that rely on sequential protein release from specialized secretory organelles for invasion and multiplication within host cells. Because of the importance of these unusual membrane trafficking pathways for drug development and comparative cell biology, characterizing them is essential. In particular, it is unclear what role retrieval mechanisms play in parasite membrane trafficking or where they operate. Previously, we showed that T. gondii's beta-COP (TgBetaCOP; a subunit of coatomer protein complex I, COPI) and retrieval reporters localize exclusively to the zone between the parasite endoplasmic reticulum (ER) and Golgi apparatus. This suggested the existence of an HDEL receptor in T. gondii. We have now identified, cloned, and sequenced this receptor, TgERD2. TgERD2 localizes in a Golgi or ER pattern suggestive of the HDEL retrieval reporter (K. M. Hager, B. Striepen, L. G. Tilney, and D. S. Roos, J. Cell Sci. 112:2631-2638, 1999). A functional assay reveals that TgERD2 is able to complement the Saccharomyces cerevisiae ERD2 null mutant. Retrieval studies reveal that stable expression of a fluorescent exogenous retrieval ligand results in a dispersal of betaCOP signal throughout the cytoplasm and, surprisingly, results in betaCOP staining of the vacuolar space of the parasite. In contrast, stable expression of TgERD2GFP does not appear to disturb betaCOP staining. In addition to TgERD2, Toxoplasma contains two more divergent ERD2 relatives. Phylogenetic analysis reveals that these proteins belong to a previously unrecognized ERD2 subfamily common to plants and alveolate organisms and as such could represent mediators of parasite-specific retrieval functions. No evidence of class 2 ERD2 proteins was found in metazoan organisms or fungi.
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PMID:Receptor for retrograde transport in the apicomplexan parasite Toxoplasma gondii. 1570 5

Aspartic proteases participate in a wide variety of cellular processes in eukaryotic organisms. The genome of the human malaria parasite Plasmodium falciparum encodes 10 aspartic protease homologs. Functions have been assigned to four of these: plasmepsins I, II, IV and histo-aspartic protease are key players in the catabolism of hemoglobin in the food vacuole. The functions of the other six remain obscure. To better understand the roles of aspartic proteases in blood stage growth and asexual reproduction of P. falciparum, we have characterized the biosynthesis, cellular location and pepstatin-binding properties of plasmepsin V (PM V). PM V is expressed over the course of asexual intraerythrocytic development. The amount of PM V in the parasite is lowest in the ring stage and increases steadily through schizogony. The proregion of this aspartic protease homolog exhibits remarkable interspecies diversity and appears not to be removed following biosynthesis. In intraerythrocytic parasites, PM V is located in the endoplasmic reticulum but not in ERD2-associated Golgi structures. Fractionation and solubilization experiments demonstrate that PM V is an integral membrane protein, a result that is consistent with the presence of a C-terminal putative transmembrane domain in the PM V sequence. In contrast to the food vacuole plasmepsins, detergent-solubilized PM V does not bind the aspartic protease inhibitor pepstatin. Together, these results strongly suggest that the role of PM V in P. falciparum is distinct from those of previously characterized plasmepsins.
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PMID:Characterization of plasmepsin V, a membrane-bound aspartic protease homolog in the endoplasmic reticulum of Plasmodium falciparum. 1602 7

Plasmodium falciparum, the causative agent of malaria, relies on a sophisticated protein secretion system for host cell invasion and transformation. Although the parasite displays a secretory pathway similar to those of all eukaryotic organisms, a classical Golgi apparatus has never been described. We identified and characterised the putative Golgi matrix protein PfGRASP, a homologue of the Golgi re-assembly stacking protein (GRASP) family. We show that PfGRASP is expressed as a 70 kDa protein throughout the asexual life cycle of the parasite. We generated PfGRASP-GFP-expressing transgenic parasites and showed that this protein is localised to a single, juxtanuclear compartment in ring-stage parasites. The PfGRASP compartment is distinct from the ER, restricted within the boundaries of the parasite and colocalises with the cis-Golgi marker ERD2. Correct subcellular localisation of this Golgi matrix protein depends on a cross-species conserved functional myristoylation motif and is insensitive to Brefeldin A. Taken together our results define the Golgi apparatus in Plasmodium and depict the morphological organisation of the organelle throughout the asexual life cycle of the parasite.
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PMID:Re-defining the Golgi complex in Plasmodium falciparum using the novel Golgi marker PfGRASP. 1630 23

The malaria parasite Plasmodium falciparum harbours a relict plastid (termed the apicoplast) that has evolved by secondary endosymbiosis. The apicoplast is surrounded by four membranes, the outermost of which is believed to be part of the endomembrane system. Nuclear-encoded apicoplast proteins have a two-part N-terminal extension that is necessary and sufficient for translocation across these four membranes. The first domain of this N-terminal extension resembles a classical signal peptide and mediates translocation into the secretory pathway, whereas the second domain is homologous to plant chloroplast transit peptides and is required for the remaining steps of apicoplast targeting. We explored the initial, secretory pathway component of this targeting process using green fluorescent reporter protein constructs with modified leaders. We exchanged the apicoplast signal peptide with signal peptides from other secretory proteins and observed correct targeting, demonstrating that apicoplast targeting is initiated at the general secretory pathway of P. falciparum. Furthermore, we demonstrate by immunofluorescent labelling that the apicoplast resides on a small extension of the endoplasmic reticulum (ER) that is separate from the cis-Golgi. To define the position of the apicoplast in the endomembrane pathway in relation to the Golgi we tracked apicoplast protein targeting in the presence of the secretory inhibitor Brefeldin A (BFA), which blocks traffic between the ER and Golgi. We observe apicoplast targeting in the presence of BFA despite clear perturbation of ER to Golgi traffic by the inhibitor, which suggests that the apicoplast resides upstream of the cis-Golgi in the parasite's endomembrane system. The addition of an ER retrieval signal (SDEL) - a sequence recognized by the cis-Golgi protein ERD2 - to the C-terminus of an apicoplast-targeted protein did not markedly affect apicoplast targeting, further demonstrating that the apicoplast is upstream of the Golgi. Apicoplast transit peptides are thus dominant over an ER retention signal. However, when the transit peptide is rendered non-functional (by two point mutations or by complete deletion) SDEL-specific ER retrieval takes over, and the fusion protein is localized to the ER. We speculate either that the apicoplast in P. falciparum resides within the ER directly in the path of the general secretory pathway, or that vesicular trafficking to the apicoplast directly exits the ER.
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PMID:Evidence for Golgi-independent transport from the early secretory pathway to the plastid in malaria parasites. 1678 49

Transmission blocking vaccines (TBVs) that target the antigens on the midgut epithelium of Anopheles mosquitoes are among the promising tools for the elimination of the malaria parasite. Characterization and analysis of effective antigens is the first step to design TBVs. Calreticulin (CRT), a lectin-like protein, from Anopheles albimanus midgut, has shown antigenic features, suggesting a promising and novel TBV target. CRT is a highly conserved protein with similar features in vertebrates and invertebrates including anopheline. We cloned the full-length crt gene from malaria vector, Anopheles stephensi (AsCrt) and explored the interaction of recombinant AsCrt protein, expressed in a prokaryotic system (pGEX-6p-1), with surface proteins of Plasmodium berghei ookinetes by immunofluorescence assay. The cellular localization of AsCrt was determined using the baculovirus expression system. Sequence analysis of the whole cDNA of AsCrt revealed that AsCrt contains an ORF of 1221 bp. The amino acid sequence of AsCrt protein obtained in this study showed 64% homology with similar protein in human. The AsCrt shares the most common features of CRTs from other species. This gene encodes a 406 amino-acid protein with a molecular mass of 46 kDa, which contains a predicted 16 amino-acid signal peptides, conserved cysteine residues, a proline-rich region, and highly acidic C-terminal domain with endoplasmic reticulum retrieval sequence HDEL. The production of GST-AsCrt recombinant protein was confirmed by Western blot analysis using an antibody against the GST protein. The FITC-labeled GST-AsCrt exhibited a significant interaction with P. berghei ookinete surface proteins. Purified recombinant GST-AsCrt, labeled with FITC, displayed specific binding to the surface of P. berghei ookinetes in comparison with control. Moreover, the expression of AsCrt in baculovirus expression system indicated that AsCrt was localized on the surface of Sf9 cells. Our results suggest that AsCrt could be utilized as a potential target for future studies in TBV area for malaria control.
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PMID:Molecular characterization of calreticulin from Anopheles stephensi midgut cells and functional assay of the recombinant calreticulin with Plasmodium berghei ookinetes. 2515 Jan 60