Anaerobic peroxisomes in Entamoeba histolytica metabolize myo-inositol

Entamoeba histolytica is believed to be devoid of peroxisomes, like most anaerobic protists. In this work, we provided the first evidence that peroxisomes are present in E. histolytica, although only seven proteins responsible for peroxisome biogenesis (peroxins) were identified (Pex1, Pex6, Pex5, Pex11, Pex14, Pex16, and Pex19). Targeting matrix proteins to peroxisomes is reduced to the PTS1-dependent pathway mediated via the soluble Pex5 receptor, while the PTS2 receptor Pex7 is absent. Immunofluorescence microscopy showed that peroxisomal markers (Pex5, Pex14, Pex16, Pex19) are present in vesicles distinct from mitosomes, the endoplasmic reticulum, and the endosome/phagosome system, except Pex11, which has dual localization in peroxisomes and mitosomes. Immunoelectron microscopy revealed that Pex14 localized to vesicles of approximately 90–100 nm in diameter. Proteomic analyses of affinity-purified peroxisomes and in silico PTS1 predictions provided datasets of 655 and 56 peroxisomal candidates, respectively; however, only six proteins were shared by both datasets, including myo-inositol dehydrogenase (myo-IDH). Peroxisomal NAD-dependent myo-IDH appeared to be a dimeric enzyme with high affinity to myo-inositol (Km 0.044 mM) and can utilize also scyllo-inositol, D-glucose and D-xylose as substrates. Phylogenetic analyses revealed that orthologs of myo-IDH with PTS1 are present in E. dispar, E. nutalli and E. moshkovskii but not in E. invadens, and form a monophyletic clade of mostly peroxisomal orthologs with free-living Mastigamoeba balamuthi and Pelomyxa schiedti. The presence of peroxisomes in E. histolytica and other archamoebae breaks the paradigm of peroxisome absence in anaerobes and provides a new potential target for the development of antiparasitic drugs.

Peroxisomal ATP uptake is managed by the ABC transporters and two adenine nucleotide transporters

Peroxisomes are essential organelles involved in various metabolic processes, including fatty acid beta-oxidation. Their metabolic functions require a controlled exchange of metabolites and co-factors, including ATP across the peroxisomal membrane. We investigated which proteins are involved in the peroxisomal uptake of ATP in the yeast Saccharomyces cerevisiae. Using wild-type and targeted deletion strains, we measured ATP-dependent peroxisomal octanoate beta-oxidation, intra-peroxisomal ATP levels employing peroxisome-targeted ATP-sensing reporter proteins, and ATP uptake in proteoliposomes prepared from purified peroxisomes. We show that intra-peroxisomal ATP levels are maintained by different peroxisomal membrane proteins each with different modes of action: (1) the previously reported Ant1p protein, which catalyzes ATP/AMP exchange (2) the ABC transporter protein complex Pxa1p/Pxa2p, which mediates both acyl-CoA and ATP uptake; and; (3) the mitochondrial Aac2p protein, which catalyzes ATP/ADP exchange and was shown to have a dual localization in both mitochondria and peroxisomes. Our results provide compelling evidence for an ingenious complementary system for the uptake of ATP in peroxisomes.

PARTICULAR QUALITIES OF THE PROTEOLYTIC SYSTEM IN PATIENTS WITH TUBERCULOSIS DEPENDING ON THE SENSITIVITY OF THE PATHOGEN

The aim: Studying the features of the proteolytic system in patients with tuberculosis depending on the sensitivity of the pathogen. Materials and methods: In the course of the research we studied the level of elastase in the blood of 111 patients. The first group consisted of 66 (59.5%) people with pulmonary tuberculosis (39 were sensitive to antibacterial drugs, 27 were resistant). The second group included 13 (11.7%) patients with tuberculous pleurisy. The third group consisted of 32 (28.8%) patients with dual localization of the process (pulmonary tuberculosis and pleural tuberculosis). Results: The level of neutrophil elastase in patients with tuberculous pleurisy (253.2 nmol / min • ml) was 2.2 times higher than in patients with sensitive pulmonary tuberculosis (110.1 nmol / min • ml) and higher than in patients with resistant pulmonary tuberculosis 3.0 times. In combined pulmonary and pleural tuberculosis (third group) the level of elastase was 1.6 times higher than in pulmonary tuberculosis (176.9 nmol / min • ml)) (p <0.01), but lower than in pleurisy in 1, 4 times. In sensitive combined tuberculosis (lungs and pleura) the level of NE was 1.5 times higher than in patients of subgroup 1a (p <0.01) and 1.4 times lower than in patients with tuberculous pleurisy (p <0.01 ). Conclusions: The highest level of elastase in tuberculous pleurisy can be explained by its increased production, contributes to increased “permeability” of the pleural sheets and the accumulation of pleural effusion. In resistant forms of tuberculosis, the immune response in the form of the activity of the proteolytic system, which is lower than in sensitive forms, can be explained by the exhaustion of the immune system under the influence of aggressive tuberculosis. The above can be associated with both the weakening of the patient’s body and the aggressiveness of the pathogen.

Impaired phosphatidylethanolamine metabolism activates a reversible stress response that detects and resolves mutant mitochondrial precursors

SUMMARYPhosphatidylethanolamine made in mitochondria has long been recognized as an important precursor for phosphatidylcholine production that occurs in the endoplasmic reticulum (ER). Recently, the strict mitochondrial localization of the enzyme that makes PE in the mitochondrion, phosphatidylserine decarboxylase 1 (Psd1), was questioned. Since a dual localization of Psd1 to the ER would have far-reaching implications, we initiated our study to independently re-assess the subcellular distribution of Psd1. Our results support the unavoidable conclusion that the vast majority, if not all, of functional Psd1 resides in the mitochondrion. Through our efforts, we discovered that mutant forms of Psd1 that impair a self-processing step needed for it to become functional are dually localized to the ER when expressed in a PE-limiting environment. We conclude that severely impaired cellular PE metabolism provokes an ER-assisted adaptive response that is capable of identifying and resolving nonfunctional mitochondrial precursors.

Functional Diversification of the Dihydroflavonol 4-Reductase from Camellia nitidissima Chi. in the Control of Polyphenol Biosynthesis

Plant secondary metabolism is complex in its diverse chemical composition and dynamic regulation of biosynthesis. How the functional diversification of enzymes contributes to the diversity is largely unknown. In the flavonoids pathway, dihydroflavonol 4-reductase (DFR) is a key enzyme mediating dihydroflavanol into anthocyanins biosynthesis. Here, the DFR homolog was identified from Camellia nitidissima Chi. (CnDFR) which is a unique species of the genus Camellia with golden yellow petals. Sequence analysis showed that CnDFR possessed not only conserved catalytic domains, but also some amino acids peculiar to Camellia species. Gene expression analysis revealed that CnDFR was expressed in all tissues and the expression of CnDFR was positively correlated with polyphenols but negatively with yellow coloration. The subcellular localization of CnDFR by the tobacco infiltration assay showed a likely dual localization in the nucleus and cell membrane. Furthermore, overexpression transgenic lines were generated in tobacco to understand the molecular function of CnDFR. The analyses of metabolites suggested that ectopic expression of CnDFR enhanced the biosynthesis of polyphenols, while no accumulation of anthocyanins was detected. These results indicate a functional diversification of the reductase activities in Camellia plants and provide molecular insights into the regulation of floral color.

A piggybacking mechanism enables peroxisomal localization of the glyoxylate cycle enzyme Mdh2 in yeast

Eukaryotic cells evolved organelles that allow the compartmentalization and regulation of metabolic processes. Knowledge on molecular mechanisms that allow temporal and spatial organization of enzymes within organelles is therefore critical for understanding eukaryotic metabolism. Here we show that the yeast malate dehydrogenase 2 (Mdh2) is dually localized to the cytosol and to peroxisomes and is targeted to peroxisomes via association with Mdh3 and a Pex5-dependent piggybacking mechanism. The dual localization of Mdh2 contributes to our understanding of the glyoxylate cycle and provides a new perspective on compartmentalization of cellular metabolism, which is critical for the perception of metabolic disorders and aging.

Localization and RNA Binding of Mitochondrial Aminoacyl tRNA Synthetases

Mitochondria contain a complete translation machinery that is used to translate its internally transcribed mRNAs. This machinery uses a distinct set of tRNAs that are charged with cognate amino acids inside the organelle. Interestingly, charging is executed by aminoacyl tRNA synthetases (aaRS) that are encoded by the nuclear genome, translated in the cytosol, and need to be imported into the mitochondria. Here, we review import mechanisms of these enzymes with emphasis on those that are localized to both mitochondria and cytosol. Furthermore, we describe RNA recognition features of these enzymes and their interaction with tRNA and non-tRNA molecules. The dual localization of mitochondria-destined aaRSs and their association with various RNA types impose diverse impacts on cellular physiology. Yet, the breadth and significance of these functions are not fully resolved. We highlight here possibilities for future explorations.

Records of RNA locations in living yeast revealed through covalent marks

RNA movements and localization pervade biology, from embryonic development to disease. To identify RNAs at specific locations, we developed a strategy in which a uridine-adding enzyme is anchored to subcellular sites, where it directly marks RNAs with 3′ terminal uridines. This localized RNA recording approach yields a record of RNA locations, and is validated through identification of RNAs localized selectively to the endoplasmic reticulum (ER) or mitochondria. We identify a broad dual localization pattern conserved from yeast to human cells, in which the same battery of mRNAs encounter both ER and mitochondria in both species, and include an mRNA encoding a key stress sensor. Subunits of many multiprotein complexes localize to both the ER and mitochondria, suggesting coordinated assembly. Noncoding RNAs in the course of RNA surveillance and processing encounter both organelles. By providing a record of RNA locations over time, the approach complements those that capture snapshots of instantaneous positions.

Endometriosis of the rectus abdominis muscles: a rare case of dual location

Endometriosis of the abdominal wall is a rare entity, the etiopathogenesis remains unclear. It most often occurs after gynecological or obstetric surgery. We report the case of a patient with a dual localization of endometriosis in the abdominal wall, the diagnosis was made by abdominal CT scan. The treatment was surgical. The pathology study confirmed the diagnosis of parietal endometriosis. The postoperative course was uneventful with a favorable outcome for 2 years without recurrence. Through our case, we will discuss the characteristics of this entity in order to understand the interest of an early diagnosis and management to deduce possible means of prevention during each gynecological or obstetric surgery.

Genome communication in plants mediated by organelle–n­ucleus-located proteins

An increasing number of eukaryotic proteins have been shown to have a dual localization in the DNA-containing organelles, mitochondria and plastids, and/or the nucleus. Regulation of dual targeting and relocation of proteins from organelles to the nucleus offer the most direct means for communication between organelles as well as organelles and nucleus. Most of the mitochondrial proteins of animals have functions in DNA repair and gene expression by modelling of nucleoid architecture and/or chromatin. In plants, such proteins can affect replication and early development. Most plastid proteins with a confirmed or predicted second location in the nucleus are associated with the prokaryotic core RNA polymerase and are required for chloroplast development and light responses. Few plastid–nucleus-located proteins are involved in pathogen defence and cell cycle control. For three proteins, it has been clearly shown that they are first targeted to the organelle and then relocated to the nucleus, i.e. the nucleoid-associated proteins HEMERA and Whirly1 and the stroma-located defence protein NRIP1. Relocation to the nucleus can be experimentally demonstrated by plastid transformation leading to the synthesis of proteins with a tag that enables their detection in the nucleus or by fusions with fluoroproteins in different experimental set-ups. This article is part of the theme issue ‘Retrograde signalling from endosymbiotic organelles’.