Chlamydia pneumoniae infection associated with multi-organ failure and fatal outcome in a previously healthy patient

Chlamydia pneumoniae has been associated with respiratory infections and with cardiovascular disease. We describe here a patient with multi-organ failure and fatal outcome in whom C. pneumoniae was implicated as a causative agent. Serological analysis for C. pneumoniae was done by immunofluorescence. Immunohistochemistry was carried out with avidin-biotin peroxidase staining. The patient had pneumonia I month prior to death. C. pneumoniae was detected in the heart and lungs by immunohistochemistry at autopsy. The patient had an antibody pattern suggestive of current or chronic C. pneumoniae infection. Serological analysis for Legionella sp., Mycoplasma pneumoniae, CMV, EBV, enteroviral agents and markers for autoimmune disease were negative. The findings suggest C. pneumoniae as the aetiological agent in this case of multi-organ failure.

The human malaria parasite Plasmodium falciparum exports the ATP-binding cassette protein PFGCN20 to membrane structures in the host red blood cell

PFGCN20 is a member of the ATP-binding cassette family of proteins that is closely related to the yeast translational regulator Gcn20p. We have generated a polyclonal antibody against the N-terminal region of PFGCN20 and studied the cellular localization of PFGCN20 throughout the erythrocytic life cycle of Plasmodium falciparum. PFGCN20 was found to be present at all stages and a pronounced export of PFGCN20 into the erythrocyte was observed in the trophozoite and schizont stages. In the indirect immunofluorescence assay, PFGCN20 was found to display significant colocalization with antigens detected by the monoclonal antibody 41E11. In contrast, there was only a minimal overlap of PFGCN20 localization with EMP2 and HRP2. Immunoelectron microscopy demonstrated a pronounced accumulation of PFGCN20 in the lumen of the parasitophorous vacuole and deconvolution fluorescence microscopy showed membrane association with selective regions of a tubovesicular network in the red cell. We also observed a concentration of PFGCN20 in electron-dense plaques just underneath the parasite's plasma membrane and an association of PFGCN20 with cytoplasmic vesicular structures within the parasite. The observed export of PFGCN20 and its association with the tubovesicular network in host red cells, may be indicative of the fact that PFGCN20 functions as ATP-binding subunit of an unknown multimeric ABC-transporter. The cytoplasmic localization of PFGCN20 in the parasite, however, suggests that the involvement of PFGCN20 in translational regulation or other cytoplasmic biological functions cannot be ruled out.

Intracellular trafficking in Plasmodium-infected erythrocytes

The past few years have witnessed considerable progress in molecular and biochemical studies of intracellular trafficking in malaria-infected red cells. Highlights include the identification of solute channels in the vacuolar membrane and the red blood cell membrane, a tubovesicular membrane network that delivers exogenous nutrients and drugs to the parasite, and parasite gene families that mediate adherence to endothelial cells and red cells.

Partitioning of the Golgi apparatus during mitosis in living HeLa cells

The Golgi apparatus of HeLa cells was fluorescently tagged with a green fluorescent protein (GFP), localized by attachment to the NH2-terminal retention signal of N-acetylglucosaminyltransferase I (NAGT I). The location was confirmed by immunogold and immunofluorescence microscopy using a variety of Golgi markers. The behavior of the fluorescent Golgi marker was observed in fixed and living mitotic cells using confocal microscopy. By metaphase, cells contained a constant number of Golgi fragments dispersed throughout the cytoplasm. Conventional and cryoimmunoelectron microscopy showed that the NAGT I-GFP chimera (NAGFP)-positive fragments were tubulo-vesicular mitotic Golgi clusters. Mitotic conversion of Golgi stacks into mitotic clusters had surprisingly little effect on the polarity of Golgi membrane markers at the level of fluorescence microscopy. In living cells, there was little self-directed movement of the clusters in the period from metaphase to early telophase. In late telophase, the Golgi ribbon began to be reformed by a dynamic process of congregation and tubulation of the newly inherited Golgi fragments. The accuracy of partitioning the NAGFP-tagged Golgi was found to exceed that expected for a stochastic partitioning process. The results provide direct evidence for mitotic clusters as the unit of partitioning and suggest that precise regulation of the number, position, and compartmentation of mitotic membranes is a critical feature for the ordered inheritance of the Golgi apparatus.

A membrane network for nutrient import in red cells infected with the malaria parasite

The human malaria parasite Plasmodium falciparum exports an interconnected network of tubovesicular membranes (the TVM) that extends from the parasite's vacuolar membrane to the periphery of the red cell. Here it is shown that extracellular solutes such as Lucifer yellow enter the TVM and are delivered to the parasite. Blocking the assembly of the network blocked the delivery of exogenous Lucifer yellow, nucleosides, and amino acids to the parasite without inhibiting secretion of plasmodial proteins. These data suggest that the TVM is a transport network that allows nutrients efficient access to the parasite and could be used to deliver antimalarial drugs directly into the parasite.

Identification and localization of rab6, separation of rab6 from ERD2 and implications for an 'unstacked' Golgi, in Plasmodium falciparum

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.

Sphingolipid synthesis and membrane formation byPlasmodium

Plasmodium falciparum is a protozoan parasite that causes the most virulent o f human malarias. The asexual blood-stage organism invades and multiplies in a vacuole in the mature erythrocyte. During intravacuolar growth, it induces the formation of a novel network o f tubovesicular membranes, the TVM, that is not present in uninfected red blood cells. Recent data suggest that sphingomyelin biosynthesis by the parasite is an essential requirement for the assembly o f the TVM. Furthermore, sphingolipid synthesis as well as the formation and function o f the TVM may provide new targets for chemotherapy against malaria parasites.

Sphingolipid synthesis as a target for chemotherapy against malaria parasites

The human malaria parasite Plasmodium falciparum contains sphingomyelin synthase in its Golgi apparatus and in a network of tubovesicular membranes in the cytoplasm of the infected erythrocyte. Palmitoyl and decanoyl analogues of 1-phenyl-2-acylamino-3-morpholino-1-propanol inhibit the enzyme activity in infected erythrocytes. An average of 35% of the activity is extremely sensitive to these drugs and undergoes a rapid, linear decrease at drug concentrations of 0.05-1 microM. The remaining 65% suffers a slower linear inhibition at drug concentrations ranging from 25 to 500 microM. Evidence is presented that inhibition of the sensitive fraction alone selectively disrupts the appearance of the interconnected tubular network in the host cell cytoplasm, without blocking secretory development at the parasite plasma membrane or in organelles within the parasite, such as the Golgi and the digestive food vacuole. This inhibition also blocks parasite proliferation in culture, indicating that the sensitive sphingomyelin synthase activity as well as the tubovesicular network may provide rational targets for drugs against malaria.

Recognition of a 170 kD protein in mammalian Golgi complexes by an antibody against malarial intraerythrocytic lamellae

Human erythrocytes infected with the malarial parasite Plasmodium falciparum contain flattened membrane lamellae. It has been suggested that the lamellae may be involved in the sorting of malarial proteins to the cytoplasm and the cell membrane of the host erythrocyte. We have previously shown that the lamellae accumulate sphingolipids by virtue of their lipid composition in a manner similar to the trans-Golgi and the trans-Golgi network in mammalian cells. In this paper, we show by immunofluorescence microscopy that a monoclonal antibody to the lamellae labeled a perinuclear organelle that colocalized with WGA and the mannose-6-phosphate receptor in cultured mammalian cells. Immunoelectron microscopy experiments revealed that LWLI labels cisternae of the trans-face and the trans-Golgi network. Western blot analysis of subcellular fractions using LWLI detected a 170 kD protein which is associated with the luminal side of Golgi membranes of rat liver and is conserved in all cell lines studied. Our results indicate that (i) the 170 kD protein is a novel marker of the mammalian trans-Golgi and the trans-Golgi network and (ii) in addition to similarities in their morphological and lipid characteristics, the lamellae induced by P. falciparum in erythrocytes share proteinaceous determinants with the Golgi apparatus of mammalian cells.

Plasmodium falciparum: protein localization along a novel, lipid-rich tubovesicular membrane network in infected erythrocytes

Erythrocytes infected with Plasmodium falciparum contain a novel network of tubovesicular membranes which can be prominently labeled by fluorescent sphingolipids and have been implicated in trafficking pathways in infected red cells. We have developed a method to simultaneously image lipids of the tubovesicular membrane network and exported parasite proteins by high-resolution confocal microscopy. Our results indicate that Exp1 (a 23-kDa protein marker of the parasitophorous vacuolar membrane and intraerythrocytic loops) concentrates in membrane domains on the periphery of the parasite and in the tubovesicular membrane network. In contrast, a 45-kDa protein localized to the Maurer's clefts is distributed in punctate domains along lipid labeled tubovesicular membranes, frequently along the periphery of the network juxtaposed to the red cell membrane. These results strongly suggest that the lipid-rich tubovesicular membranes are a complex network containing domains of parasite proteins.

Biosynthesis, export and processing of a 45 kDa protein detected in membrane clefts of erythrocytes infected with Plasmodium falciparum

During its asexual life cycle, the human malaria parasite Plasmodium falciparum exports numerous proteins beyond its surface to its host erythrocyte. We have studied the biosynthesis, processing and export of a 45 kDa parasite protein resident in membrane clefts in the erythrocyte cytoplasm. Our results indicate that this cleft protein is made as a single tightly membrane-bound 45 kDa polypeptide in ring- and trophozoite-infected erythrocytes (0-36 h in the life cycle). Using ring/trophozoite parasites released from erythrocytes, the 45 kDa protein is shown to be efficiently transported to the cell surface. This export is specifically blocked by the drug brefeldin A, and at 15 and 20 degrees C. These results indicate that transport blocks seen in the Golgi of mammalian cells are conserved in P. falciparum. Further, the newly synthesized 45 kDa protein passes through parasite Golgi compartments before its export to clefts in the erythrocyte. In mid-to-late-ring-infected erythrocytes, a fraction of the newly synthesized 45 kDa protein is processed to a second membrane-bound phosphorylated 47 kDa protein. The t1/2 of this processing step is about 4 h, suggesting that it occurs subsequent to protein export from the parasite. Evidence is presented that, in later trophozoite stages (24-36 h), the exported 45 and 47 kDa proteins are partially converted into soluble molecules in the intraerythrocytic space. Taken together, the results indicate that the lower eukaryote P. falciparum modulates a classical secretory pathway to support membrane export beyond its plasma membrane to clefts in the erythrocyte. Subsequent to export, phosphorylation and/or conversion into a soluble form may regulate the interactions of the 45 kDa protein with the clefts during parasite development.

Plasmodium falciparum exports the Golgi marker sphingomyelin synthase into a tubovesicular network in the cytoplasm of mature erythrocytes

This work describes two unusual features of membrane development in a eukaryotic cell. (a) The induction of an extensive network of tubovesicular membranes by the malaria parasite Plasmodium falciparum in the cytoplasm of the mature erythrocyte, and its visualization with two ceramide analogues C5-DMB-ceramide and C6-NBD-ceramide. "Sectioning" of the infected erythrocytes using laser confocal microscopy has allowed the reconstruction of detailed three-dimensional images of this novel membrane network. (b) The stage-specific export of sphingomyelin synthase, a biosynthetic activity concentrated in the Golgi of mammalian cells, to this tubovesicular network. Evidence is presented that in the extracellular merozoite stage the parasite retains sphingomyelin synthase within its plasma membrane. However, intracellular ring- and trophozoite-stage parasites export a substantial fraction (approximately 26%) of sphingomyelin synthase activity to membranes beyond their plasma membrane. Importantly we do not observe synthesis of new enzyme during these intracellular stages. Taken together these results strongly suggest that the export of this classic Golgi enzyme is developmentally regulated in Plasmodium. We discuss the significance of this export and the tubovesicular network with respect to membrane development and function in the erythrocyte cytosol.

Identification and localization of ERD2 in the malaria parasite Plasmodium falciparum: separation from sites of sphingomyelin synthesis and implications for organization of the Golgi

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.

Export of parasite proteins to the erythrocyte in Plasmodium falciparum-infected cells

The human malaria parasite Plasmodium falciparum invades erythrocytes and develops within a parasitophorous vacuole. It has been proposed that constitutive protein export from the intracellular parasite is mediated by two types of secretory vesicles. One is targeted to the parasite plasma membrane and the other to a domain where the plasma and vacuolar membranes of the parasite are fused into a single bilayer. This differential targeting of vesicles may be regulated by the developmental stage of the parasite. Regulated secretion through the apical organelles at or immediately after the invasion of a new red cell may allow protein insertion at the erythrocyte surface and mediate formation of the joint membrane domain of constitutive secretion.

Secretory transport in Plasmodium

The asexual blood stage of the human malaria parasite Plasmodium falciparum resides within the mature erythrocyte - a cell that has no intracellular organelles and few biosynthetic activities. However, Plasmodium, as on actively growing and dividing cell, has numerous requirements for the uptake o f nutrients and expulsion of waste. Hence, the parasite must extensively remodel the erythrocyte to facilitate its survival, not only by exporting numerous proteins, but also by providing the requisite machinery for their .trafficking. In this review, Heidi Elmendorf and Kastun Haldar propose a model for secretion in P. falciparum.

Lipid transport in Plasmodium

During intraerythrocytic development, the human malaria parasite Plasmodium falciparum actively internalizes phospholipids from its erythrocyte membrane and the extracellular medium. The import of exogenous lipids is not due to endocytosis, but to energy-dependent, transbilayer movement of phospholipids induced by the parasite in the erythrocyte surface. Novel tubular membranes that appear to emerge from the vacuole of the parasite and extend into the erythrocyte cytoplasm are labeled by exogenously added fluorescent lipids. These tubules interact with the erythrocyte membrane, but definitive evidence for their role in catalyzing transbilayer phospholipid movement in the red blood cell bilayer is still not available. Both biochemical and microscopic studies indicate that all lipid analogs internalized into the intraerythrocytic compartments and/or the parasite are not exported back to the host cell surface. Nonexchangeable fluorescent lipids are exported from a parasite to its intraerythrocytic tubules, but not to an adjacent parasite in a double-infected red blood cell. Thus, while the intraerythrocytic membranes engage in prominent tubular development at the vacuolar surface and deliver lipids to the parasite they originate from, they appear to be incapable of vesicular or tubular membrane export across the erythrocyte cytosol. Parasite Golgi activities for the synthesis and accumulation of sphingomyelin are detected in the intraerythrocytic tubules, indicating a novel export of classic secretory functions to their lumen, which could be central to both tubular development and lipid-sorting activities in these organelles.

A transferrin-independent iron uptake activity in Plasmodium falciparum-infected and uninfected erythrocytes

Non-heme iron is essential for the asexual growth of the human malaria parasite Plasmodium falciparum in mature erythrocytes. Utilization of iron bound to serum transferrin by the parasitized cells has been postulated, but direct evidence for its specific delivery has not been reported. Here we demonstrate that normal levels of transferrin in human serum are not required for intraerythrocytic P. falciparum growth: culture medium immunodepleted 500-1000 fold in human transferrin was capable of supporting parasitemias and rates of invasion comparable to those observed in non-depleted medium. 55Fe bound to transferrin was not taken up by infected cells. A transferrin-independent non-heme iron uptake activity was, however, detected in both infected and uninfected erythrocytes when iron was presented to the cells as 55Fe-NTA or 55Fe-citrate. Although the uptake activity was not parasite specific, the radiolabel was found in association with parasites mechanically released from the infected erythrocytes, indicating that it is delivered to the intracellular organism. Evidence is presented that the transferrin-independent iron uptake activity is time-, temperature- and concentration-dependent, but apparently not energy-dependent.

Brefeldin A inhibits protein secretion and parasite maturation in the ring stage of Plasmodium falciparum

The release of all newly synthesized soluble proteins from the ring stage of Plasmodium falciparum-infected erythrocytes was reversibly blocked by brefeldin A, indicating the presence of a conserved step of classical eukaryotic secretory export within the parasite. This implies that proteins exported to the erythrocyte cytosol undergo secretory release at the parasite plasma membrane and subsequent translocation across the vacuolar membrane. Along with inhibiting protein export brefeldin arrested parasite maturation, but the cells remained viable even after 24 h in the presence of the drug. The results suggest that secretory export may be important for development, but not for immediate survival, at the ring stage.

Synthesis and secretion of proteins by released malarial parasites

Controlled mechanical homogenization of Plasmodium falciparum-infected erythrocytes releases parasites of a quality sufficient for studying the export of newly synthesized plasmodial proteins. Protein synthesis occurs within intact released parasites as defined by resistance of acid-insoluble incorporation of radiolabel to high levels of exogenously added EDTA, hexokinase, and RNaseA. While exogenously added ATP and erythrocyte cytosol were not essential for biosynthetic activity at levels comparable to that seen in infected erythrocytes, the addition of an extracellular ATP regenerating system (ARS) stimulated the synthesis of parasite proteins. Conversely, parasite viability and biosynthetic activity are decreased by the addition of a non-hydrolyzable ATP analogue (ATP gamma S), ADP, or ATP in the absence of a regenerating system. These data suggest a metabolic interdependence between extracellular energy metabolism and biosynthetic functions within the parasite. The export of a predominant subset of proteins was retarded in the presence of Brefeldin A, indicating the existence of a classical secretory pathway characteristic of that seen in higher eukaryotic cells. Interestingly, a Brefeldin A-insensitive component of export was also consistently observed; this may suggest the existence of an additional alternative secretory mechanism in malaria.

The movement of fluorescent endocytic tracers in Plasmodium falciparum infected erythrocytes

The fluorescent lipophilic probe 1,1'-dihexadecyl-3-3'-3-3'- tetramethylindocarbocyanine (diIC16) inserted in the red cell surface, functioned as a non-exchangeable lipid marker which was not metabolised or toxic in plasmodial cultures. Invasion by Plasmodium falciparum resulted in the internalisation of the lipid, suggesting the uptake of red cell membrane components during parasite entry. The fluorescent lipid was not transported from red cell to parasite membranes at subsequent stages of development, but label in the erythrocyte-derived parasitophorous vacuole was eventually detected in daughter merozoites. Fluorescent dextrans of 10 kDa in the extracellular medium were also not internalised during intraerythrocytic parasite growth. The results support that with the exception of the invasion step, plasmodial infection does not induce endocytosis in the erythrocyte membrane. Despite the lack of endocytosis, both D and L stereoisomers of the head group blocked phospholipid analogue N-4-nitrobenzo-2-oxa-1,3-diazoledipalmitoyl phosphatidylethanolamine (N-NBD-PE) inserted in the erythrocyte membrane, were internalised by mature infected erythrocytes. Lipid internalisation occurred by a non head group dependent parasite mechanism, which could account for the stage-specific uptake of phospholipids observed in mature infected erythrocytes. We were unable to detect the transport of carbocyanine dyes and N-NBD-PE from intracellular parasites back to the erythrocyte membrane. Additionally, the carbocyanine dyes were not transferred between adjacent organisms in a double infected red cell. The data argue for the absence of bulk membrane lipid transport between individual parasites and their host cell bilayer in an infected erythrocyte.

Labeling and initial characterization of polar lipids in cultures of Plasmodium falciparum

The present report describes the radioactive labeling of polar lipids in in vitro cultures of Plasmodium falciparum as well as their extraction with organic solvents and their partial characterization by chemical and enzymatic methods. All substances detected could be cleaved by alkali, suggesting that they were esters rather than sphingolipids or compounds containing alkyl groups. Dolichol-cycle intermediates were not detected. Phosphatidylinositol, phosphatidylethanolamine, and phosphatidylcholine were labeled by fatty acids and inositol or ethanolamine, respectively, confirming their de novo synthesis by the parasite. Metabolic labeling with glucosamine and cleavage by phosphatidylinositol-specific phospholipase C provided evidence of the formation of N-acetyl-glucosaminyl-phosphatidylinositol, an obligate precursor in the biosynthesis of glycosylphosphatidylinositol membrane anchors of proteins.

Stage-specific expression of plasmodial proteins containing an antigenic marker of the intraerythrocytic cisternae

A monoclonal antibody, LWLI, recognized 3 proteins of 45, 50 and 102 kDa in Plasmodium falciparum-infected erythrocytes. The 45- and 50-kDa proteins were parasite-encoded and displayed markedly different peptide maps, indicating that they were distinct plasmodial polypeptides with a common antigenic epitope rather than differentially processed forms of a primary translational product. The 45-kDa protein was present throughout intraerythrocytic growth, while the 50-kDa molecule was not detected earlier than 11 h in the life cycle. The 102-kDa protein was only expressed in trophozoite- and schizont-infected red cells: its structural relationship to the 45- and 50-kDa proteins, if any, remains undefined. By indirect immunofluorescence and immunoelectron microscopy, LWLI bound to flattened intraerythrocytic cisternae exported into the erythrocyte cytoplasm. The results support the theory that proteins recognized by the antibody were concentrated in these compartments and their common antigenic epitope may serve as a marker for the cisternae. Stage-specific expression of LWLI reactive proteins implicates developmental regulation of cisternal functions during asexual parasite development.