Browsing by Author "Hoppe, Heinrich C"

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    Actin is required for endocytic trafficking in the malaria parasite Plasmodium falciparum
    (Wiley, 2008) Smythe, Wynand A; Joiner, Keith A; Hoppe, Heinrich C
    The intra-erythrocytic stages of the malaria parasite endocytose large quantities of the surrounding erythrocyte cytoplasm and deliver it to a digestive food vacuole via endocytic vesicles. Digestion provides amino acids for parasite protein synthesis and is required to maintain the osmotic integrity of the host cell. The parasite endocytic pathway has been described morphologically by electron microscopy, but the molecular mechanisms that mediate and regulate it remain elusive. Given the involvement of actin in endocytosis in other eukaryotes, we have used actin inhibitors to assess the requirement for this protein in the endocytic pathway of the human malaria parasite, Plasmodium falciparum. Treatment of cultures with cytochalasin D did not affect haemoglobin levels in the parasites when co-administered with protease inhibitors, and neither did it affect the uptake of the endocytic tracer horseradish peroxidase, suggesting the absence of actin in the mechanism of endocytosis. However, in the absence of protease inhibitors, treated parasites contained increased levels of haemoglobin due to an accumulation of enlarged endocytic vesicles, as determined by immunofluorescence and electron microscopy, suggesting a role for actin in vesicle trafficking, possibly by mediating vesicle maturation and/or fusion to the digestive vacuole. In contrast to cytochalasin D, treatment with jasplakinolide led to an inhibition of endocytosis, an accumulation of vesicles closer to the plasma membrane and a marked concentration of actin in the parasite cortex. We propose that the stabilization of cortical actin filaments by jasplakinolide interferes with normal endocytic vesicle formation and migration from the cell periphery.
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    Characterising the role of actin and PI (3) kinases in endocytosis in the malaria parasite Plasmodium falciparum
    (2007) Smythe, Wynand Anton; Hoppe, Heinrich C
    By contrast to mammalian cells, very little is known about endocytosis in the malaria parasite. However, endocytosis via the cytostome is required by the parasite to ingest haemoglobin from its host cytosol which it transports within double membrane vesicles to the digestive vacuole, where digestion occurs and metabolites are used mostly for nutritional purposes. To gain a deeper understanding of the molecular basis and mechanisms of this vital process, a panel of inhibitors was used to inhibit the actin cytoskeleton and PI (3) kinases in the parasite. In this study Cytochalasin D and Latrunculin A, which depolymerise and prevent actin fimalment formation, Jasplakinolide, which stabilises actin filaments, and Wormannin and LY294002, which inhibit PI 93) kinase, were used to study actin disrupting and PI (3) kinase inhibiting drug effects on haemoglobin endocytosis and transport vesicle trafficking within the malaria parasite Plasmodium falciparum.
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    The characterization of adaptor protein homologues in Plasmodium falciparum
    (2009) Meredith, Sandra Allison; Hoppe, Heinrich C
    Plasmodium falciparum is becoming increasingly more resistant to regular antimalarial drugs, making it necessary to identify novel drug candidates and drug targets. Components of the endocytic and secretory pathway in asexual stage parasites are attractive targets because they play a fundamental role in the normal processes of parasite metabolism. Adaptor protein complexes are components of protein coats that associate with transport vesicles of the endocytic and secretory pathways in mammalian cells. Homologues of several adaptor protein subunits are encoded by the parasite genome. The presence of these genes suggests that the parasite experiences clathrin-mediated transport processes. This study reports the cloning and characterization of selected malarial homologues of these adaptor proteins, namely three medium (μ) chain adaptin homologues and two sigma (σ) chains.
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    The effect of quinoline anti-malarial drugs on the endolysosomal and secretory pathways of plasmodium falciparum strain 3D7, dictyostelium discoideum and mammalian A549 cells
    (2007) Roberts, Lindi; Hoppe, Heinrich C
    The precise mechanisms of action of the quinoline anti-malarial drugs are uncertain, although they have been found to influence endocytosis, vesicular processing and secretion in malarial parasites and mammalian cells. In this study, the effects of chloroquine, amadiaquine, halofantrine, mefloquine and quinine on the endolysosomal systems in Plasmodium falciparum 3D7, Dictyostelium discoideum and A549 pulmonary cancer cells were examined.
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    Single and hybrid antimalarials based on artemisinin, chloroquine and ß-lactams : synthesis, antiplasmodial activity, cytotoxicity and effect of selected artemisinin-chloroquine hybrids on the parasitic endocytosis pathway
    (2009) Feng, Tzu-Shean; Chibale, Kelly; Hoppe, Heinrich C
    Malaria remains to be one of the leading causes of morbidity and mortality throughout recorded history. It is caused by protozoan parasites of the genus Plasmodium, where P. falciparum is the most lethal. Current estimates are that over 500 million people are afflicted, while 3 million people die annually. With the emergence of resistance to antimalarial drugs in the malaria parasite, it is critical to develop new chemotherapeutic agents that can combat the disease and/or overcome resistance. This may be achieved by identifying molecules that target or interfere with unique parasitic pathways such as haemoglobin degradation or parasitic endocytosis. This thesis describes the design and synthesis of novel antimalarial agents based on the ‘Designed Multiple Ligand’ approach. Compounds were synthesized via conjugate addition or multi-component condensation reaction. 4-Aminoquinolines were hybridized with artemisinin or 1,4-naphthoquinone derivatives; selected hybrids were further investigated for their effect on the parasitic endocytosis pathway and compared to the effect of chloroquine and artemisinin on the same pathway. The effects of drug treatment on the morphology and haemoglobin levels in the parasites as well as localization of transport vesicles via immunofluorescence microscopy were determined. A series of β-lactam derivatives containing a terminal acetylene moiety were synthesized via the Staudinger and Ugi 3-component 4-centre condensation reactions. The compound with the best activity from the series was used to couple these reactions to post-condensation chemical modifications via the Mannich reaction, another multi-component reaction, to create a more diversified library. A small series of 4-aminoquinoline analogues, including amodiaquine-like compounds and bisquinoline derivatives, was also prepared in an attempt to elucidate their structure-activity relationships. The antiplasmodial and cytotoxic activities were determined for all compounds; where applicable, assays on β-haematin inhibitory activity were also carried out.