The evolution and function of co-chaperones in mitochondria.

Mitochondrial chaperones mediate and affect critical organellar processes, essential for cellular function. These chaperone systems have both prokaryotic and eukaryotic features. While some of the mitochondrial co-chaperones have clear homologues in prokaryotes, some are unique to eukaryotes and have no homologues in the chaperone machinery of other cellular compartments.

Cell-cell communication between malaria-infected red blood cells via exosome-like vesicles.

Cell-cell communication is an important mechanism for information exchange promoting cell survival for the control of features such as population density and differentiation. We determined that Plasmodium falciparum-infected red blood cells directly communicate between parasites within a population using exosome-like vesicles that are capable of delivering genes. Importantly, communication via exosome-like vesicles promotes differentiation to sexual forms at a rate that suggests that signaling is involved.

The core components of organelle biogenesis and membrane transport in the hydrogenosomes of Trichomonas vaginalis.

Trichomonas vaginalis is a parasitic protist of the Excavata group. It contains an anaerobic form of mitochondria called hydrogenosomes, which produce hydrogen and ATP; the majority of mitochondrial pathways and the organellar genome were lost during the mitochondrion-to-hydrogenosome transition. Consequently, all hydrogenosomal proteins are encoded in the nucleus and imported into the organelles.

The reducible complexity of a mitochondrial molecular machine.

Molecular machines drive essential biological processes, with the component parts of these machines each contributing a partial function or structural element. Mitochondria are organelles of eukaryotic cells, and depend for their biogenesis on a set of molecular machines for protein transport. How these molecular machines evolved is a fundamental question.

Jid1 is a J-protein functioning in the mitochondrial matrix, unable to directly participate in endoplasmic reticulum associated protein degradation.

J-proteins are a class of molecular chaperones that serve to stimulate the activity of Hsp70s and are often located to recruit Hsp70 to a particular cellular function. Protein degradation associated with the endoplasmic reticulum (ERAD) is one such cellular process that requires Hsp70 on both faces of the endoplasmic reticulum. At least five J-proteins, including Jid1 (DnaJ protein Involved in ER-associated Degradation), have been implicated in controlling ERAD.

The direct route: a simplified pathway for protein import into the mitochondrion of trypanosomes.

Trypanosoma brucei is a unicellular eukaryote that causes the deadly human African trypanosomiasis ('sleeping sickness') in humans. The parasite has a complicated lifestyle, it developmentally changes aspects of its mitochondrial function as it alternates from forms in the tsetse fly to forms adapted for life in the human bloodstream. The single mitochondrion found in each trypanosome has to be duplicated precisely in each round of the cell cycle in order for parasites to replicate, and this depends on the import of proteins from the cytosol.

Microsporidian mitosomes retain elements of the general mitochondrial targeting system.

Microsporidia are intracellular parasites that infect a variety of animals, including humans. As highly specialized parasites, they are characterized by a number of unusual adaptations, many of which are manifested as extreme reduction at the molecular, biochemical, and cellular levels. One interesting aspect of reduction is the mitochondrion.

Giardia mitosomes and trichomonad hydrogenosomes share a common mode of protein targeting.

Mitochondria are archetypal organelles of endosymbiotic origin in eukaryotic cells. Some unicellular eukaryotes (protists) were considered to be primarily amitochondrial organisms that diverged from the eukaryotic lineage before the acquisition of the premitochondrial endosymbiont, but their amitochondrial status was recently challenged by the discovery of mitochondria-like double membrane-bound organelles called mitosomes. Here, we report that proteins targeted into mitosomes of Giardia intestinalis have targeting signals necessary and sufficient to be recognized by the mitosomal protein import machinery.

The J-protein family: modulating protein assembly, disassembly and translocation.

DnaJ is a molecular chaperone and the prototypical member of the J-protein family. J proteins are defined by the presence of a J domain that can regulate the activity of 70-kDa heat-shock proteins. Sequence analysis on the genome of Saccharomyces cerevisiae has revealed 22 proteins that establish four distinguishing structural features of the J domain: predicted helicity in segments I-IV, precisely placed interhelical contact residues, a lysine-rich surface on helix II and placement of the diagnostic sequence HPD between the predicted helices II and III.