Giardia lamblia Expresses a Proteobacterial-like DnaK Homolog
ABSTRACT We identified a novel gene encoding molecular chaperone HSP70 in the amitochondriate parasite Giardia lamblia. The predicted protein is similar to bacterial DnaK and mitochondrial HSP70s. The gene is transcribed and translated at a constant level during trophozoite growth and encystation. Alignment of the sequence with a data set of cytosolic, endoplasmic reticulum (ER), mitochondrial, and DnaK HSP70 homologs indicated that the sequence was extremely divergent and contained insertions unique to giardial HSP70s. Phylogenetic analyses demonstrated that this sequence was distinct from the cytosolic and ER forms and was most similar to proteobacterial and mitochondrial DnaKs. However, a specific relationship with the alpha proteobacterial and mitochondrial sequences was not strongly supported by phylogenetic analyses of this data set, in contrast to similar analyses of cpn60. These data neither confirm nor reject the possibility that this gene is a relic of secondary mitochondrial loss; they leave open the possibility that it was acquired in a separate endosymbiotic event.
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ABSTRACT: The mitochondria have arisen as a consequence of endosymbiosis of an ancestral α-proteobacterium with a methane-producing archae. The main function of the canonical aerobic mitochondria include ATP generation via oxidative phosphorylation, heme and phospholipid synthesis, calcium homeostasis, programmed cell death, and the formation of iron-sulfur clusters. Under oxygen-restricted conditions, the mitochondrion has often undergone remarkable reductive alterations of its content and function, leading to the generation of mitochondrion-related organelles (MROs), such as mitosomes, hydrogenosomes, and mithochondrion-like organelles, which are found in a wide range of anaerobic/microaerophilic eukaryotes that include several medically important parasitic protists such as Entamoeba histolytica, Giardia intestinalis, Trichomonas vaginalis, Cryptosporidium parvum, Blastocystis hominis, and Encephalitozoon cuniculi, as well as free-living protists such as Sawyeria marylandensis, Neocallimastix patriciarum, and Mastigamoeba balamuthi. The transformation from canonical aerobic mitochondria to MROs apparently have occurred in independent lineages, and resulted in the diversity of their components and functions. Due to medical and veterinary importance of the MRO-possessing human- and animal-pathogenic protozoa, their genomic, transcriptomic, proteomic, and biochemical evidence has been accumulated. Detailed analyses of the constituents and functions of the MROs in such anaerobic pathogenic protozoa, which reside oxygen-deprived or oxygen-poor environments such as the mammalian intestine and the genital organs, should illuminate the current evolutionary status of the MROs in these organisms, and give insight to environmental constraints that drive the evolution of eukaryotes and their organelles. In this review, we summarize and discuss the diverse metabolic functions and protein transport systems of the MROs from anaerobic parasitic protozoa.Biochimie 12/2013; 100C. DOI:10.1016/j.biochi.2013.11.018 · 3.12 Impact Factor
Chapter: Taxonomy of Giardia Species[Show abstract] [Hide abstract]
ABSTRACT: The taxonomy of Giardia has been controversial for well over 100 years, resulting in a confusing nomenclature with different names often being used for the same species. This has led to uncertainty in our understanding of the epidemiology of Giardia infections, and particularly the question of host specificity and zoonotic transmission. The lack of morphological characters on which to base a species level taxonomy for the forms of Giardia that infect mammals has not allowed these issues to be resolved. It is only recently that PCR-based tools have been developed and applied directly to isolates of Giardia from a range of mammalian species. As a consequence, the taxonomy of Giardia can now be revised providing a more effective platform for epidemiological studies and importantly, improving communication between researchers in the field.12/2010: pages 3-15;
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ABSTRACT: Giardia lamblia, a flagellate protozoan that parasitizes the upper small intestine of humans, is one of the most common causes of diarrheal disease worldwide. Giardia has a simple life cycle, alternating between the disease-causing trophozoites and the infective cysts. Giardia is a true eukaryotic organism since it has two nuclei, an endomembranous system including the nuclear envelope/endoplasmic reticulum, transport vesicles and lysosomes-like peripheral vacuoles, as well as a complex cytoskeleton. However, trophozoites possess several prokaryotic features, including bacterial metabolic pathways and the lack of organelles typical of higher eukaryotes, such as mitochondria, peroxisomes, and a recognizable Golgi apparatus. Despite these characteristics, Giardia carries out secretory events implying both constitutive and regulated trafficking pathways. Here we describe the secretory machinery employed by Giardia for intracellular transport of cyst wall materials, their exocytosis, and the extracellular assembly of the protective cyst wall. These processes are essential for both the survival of the parasite outside the host’s intestine and transmission of the disease among susceptible individuals.