140,901 research outputs found
Protein trafficking through the endosomal system prepares intracellular parasites for a home invasion
Toxoplasma (toxoplasmosis) and Plasmodium (malaria) use unique secretory organelles for migration, cell invasion, manipulation of host cell functions, and cell egress. In particular, the apical secretory micronemes and rhoptries of apicomplexan parasites are essential for successful host infection. New findings reveal that the contents of these organelles, which are transported through the endoplasmic reticulum (ER) and Golgi, also require the parasite endosome-like system to access their respective organelles. In this review, we discuss recent findings that demonstrate that these parasites reduced their endosomal system and modified classical regulators of this pathway for the biogenesis of apical organelles
Cooperative protein transport in cellular organelles
Compartmentalization into biochemically distinct organelles constantly
exchanging material is one of the hallmarks of eukaryotic cells. In the most
naive picture of inter-organelle transport driven by concentration gradients,
concentration differences between organelles should relax. We determine the
conditions under which cooperative transport, i.e. based on molecular
recognition, allows for the existence and maintenance of distinct organelle
identities. Cooperative transport is also shown to control the flux of material
transiting through a compartmentalized system, dramatically increasing the
transit time under high incoming flux. By including chemical processing of the
transported species, we show that this property provides a strong functional
advantage to a system responsible for protein maturation and sorting.Comment: 9 pages, 5 figure
Analysis of two genomes from the mitochondrion-like organelle of the intestinal parasite Blastocystis: complete sequences, gene content, and genome organization.
Acquisition of mitochondria by the ancestor of all living eukaryotes represented a crucial milestone in the evolution of the eukaryotic cell. Nevertheless, a number of anaerobic unicellular eukaryotes have secondarily discarded certain mitochondrial features, leading to modified organelles such as hydrogenosomes and mitosomes via degenerative evolution. These mitochondrion-derived organelles have lost many of the typical characteristics of aerobic mitochondria, including certain metabolic pathways, morphological traits, and, in most cases, the organellar genome. So far, the evolutionary pathway leading from aerobic mitochondria to anaerobic degenerate organelles has remained unclear due to the lack of examples representing intermediate stages. The human parasitic stramenopile Blastocystis is a rare example of an anaerobic eukaryote with organelles that have retained some mitochondrial characteristics, including a genome, whereas they lack others, such as cytochromes. Here we report the sequence and comparative analysis of the organellar genome from two different Blastocystis isolates as well as a comparison to other genomes from stramenopile mitochondria. Analysis of the characteristics displayed by the unique Blastocystis organelle genome gives us an insight into the initial evolutionary steps that may have led from mitochondria to hydrogenosomes and mitosomes
Protein import into the endosymbiotic organelles of apicomplexan parasites
The organelles of endosymbiotic origin, plastids, and mitochondria, evolved through the serial acquisition of endosymbionts by a host cell. These events were accompanied by gene transfer from the symbionts to the host, resulting in most of the organellar proteins being encoded in the cell nuclear genome and trafficked into the organelle via a series of translocation complexes. Much of what is known about organelle protein translocation mechanisms is based on studies performed in common model organisms; e.g., yeast and humans or Arabidopsis. However, studies performed in divergent organisms are gradually accumulating. These studies provide insights into universally conserved traits, while discovering traits that are specific to organisms or clades. Apicomplexan parasites feature two organelles of endosymbiotic origin: a secondary plastid named the apicoplast and a mitochondrion. In the context of the diseases caused by apicomplexan parasites, the essential roles and divergent features of both organelles make them prime targets for drug discovery. This potential and the amenability of the apicomplexan Toxoplasma gondii to genetic manipulation motivated research about the mechanisms controlling both organelles’ biogenesis. Here we provide an overview of what is known about apicomplexan organelle protein import. We focus on work done mainly in T. gondii and provide a comparison to model organisms
Toxoplasma gondii Syntaxin 6 is required for vesicular transport between endosomal-like compartments and the Golgi Complex
Apicomplexans are obligate intracellular parasites that
invade the host cell in an active process that relies on
unique secretory organelles (micronemes, rhoptries and
dense granules) localized at the apical tip of these highly
polarized eukaryotes. In order for the contents of these
specialized organelles to reach their final destination,
these proteins are sorted post-Golgi and it has been
speculated that they pass through endosomal-like
compartments (ELCs), where they undergo maturation.
Here, we characterize a Toxoplasma gondii homologue
of Syntaxin 6 (TgStx6), a well-established marker for
the early endosomes and trans Golgi network (TGN) in
diverse eukaryotes. Indeed, TgStx6 appears to have a
role in the retrograde transport between ELCs, the TGN
and the Golgi, because overexpression of TgStx6 results
in the development of abnormally shaped parasites
with expanded ELCs, a fragmented Golgi and a defect
in inner membrane complex maturation. Interestingly,
other organelles such as the micronemes, rhoptries and
the apicoplast are not affected, establishing the TGN
as a major sorting compartment where several transport
pathways intersect. It therefore appears thatToxoplasma
has retained a plant-like secretory pathway
- …