The microaerophilic flagellate, Trichomonas vaginalis, contains unusual acyl lipids but no detectable cardiolipin

The divergent ER-mitochondria encounter structures (ERMES) are conserved in parabasalids but lost in several anaerobic lineages with hydrogenosomes

BACKGROUND

The endoplasmic reticulum (ER)-mitochondria membrane contact sites (MCS) are extensively studied in aerobic eukaryotes; however, little is known about MCS in anaerobes with reduced forms of mitochondria named hydrogenosomes. In several eukaryotic lineages, the direct physical tether between ER and the outer mitochondrial membrane is formed by ER-mitochondria encounter structure (ERMES). The complex consists of four core proteins (Mmm1, Mmm2, Mdm12, and Mdm10) which are involved in phospholipid trafficking. Here we investigated ERMES distribution in organisms bearing hydrogenosomes and employed Trichomonas vaginalis as a model to estimate ERMES cellular localization, structure, and function.

RESULTS

Homology searches revealed that Parabasalia-Anaeramoebae, anaerobic jakobids, and anaerobic fungi are lineages with hydrogenosomes that retain ERMES, while ERMES components were gradually lost in Fornicata, and are absent in Preaxostyla and Archamoebae. In T. vaginalis and other parabasalids, three ERMES components were found with the expansion of Mmm1. Immunofluorescence microscopy confirmed that Mmm1 localized in ER, while Mdm12 and Mmm2 were partially localized in hydrogenosomes. Pull-down assays and mass spectrometry of the ERMES components identified a parabasalid-specific Porin2 as a substitute for the Mdm10. ERMES modeling predicted a formation of a continuous hydrophobic tunnel of TvMmm1-TvMdm12-TvMmm2 that is anchored via Porin2 to the hydrogenosomal outer membrane. Phospholipid-ERMES docking and Mdm12-phospholipid dot-blot indicated that ERMES is involved in the transport of phosphatidylinositol phosphates. The absence of enzymes involved in hydrogenosomal phospholipid metabolism implies that ERMES is not involved in the exchange of substrates between ER and hydrogenosomes but in the unidirectional import of phospholipids into hydrogenosomal membranes.

CONCLUSIONS

Our investigation demonstrated that ERMES mediates ER-hydrogenosome interactions in parabasalid T. vaginalis, while the complex was lost in several other lineages with hydrogenosomes.

Ceramide Phosphoethanolamine as a Possible Marker of Periodontal Disease

Periodontal disease is a chronic oral inflammatory disorder initiated by pathobiontic bacteria found in dental plaques—complex biofilms on the tooth surface. The disease begins as an acute local inflammation of the gingival tissue (gingivitis) and can progress to periodontitis, which eventually leads to the formation of periodontal pockets and ultimately results in tooth loss. The main problem in periodontology is that the diagnosis is based on the assessment of the already obvious tissue damage. Therefore, it is necessary to improve the current diagnostics used to assess periodontal disease. Using lipidomic analyses, we show that both crucial periodontal pathogens, Porphyromonas gingivalis and Tannerella forsythia, synthesize ceramide phosphoethanolamine (CPE) species, membrane sphingolipids not typically found in vertebrates. Previously, it was shown that this particular lipid can be specifically detected by an aegerolysin protein, erylysin A (EryA). Here, we show that EryA can specifically bind to CPE species from the total lipid extract from P. gingivalis. Furthermore, using a fluorescently labelled EryA-mCherry, we were able to detect CPE species in clinical samples of dental plaque from periodontal patients. These results demonstrate the potential of specific periodontal pathogen-derived lipids as biomarkers for periodontal disease and other chronic inflammatory diseases.

Aegerolysins: Lipid-binding proteins with versatile functions

Proteins of the aegerolysin family span many kingdoms of life. They are relatively widely distributed in bacteria and fungi, but also appear in plants, protozoa and insects. Despite being produced in abundance in cells at specific developmental stages and present in secretomes, only a few aegerolysins have been studied in detail. In particular, their organism-specific physiological roles are intriguing. Here, we review published findings to date on the distribution, molecular interactions and biological activities of this family of structurally and functionally versatile proteins, the aegerolysins.

Eicosapentaenoic Acid Modulates Trichomonas vaginalis Activity

Trichomonas vaginalis is a sexually transmitted parasite and, while it is often asymptomatic in males, the parasite is associated with disease in both sexes. Metronidazole is an effective treatment for trichomoniasis, but resistant strains have evolved and, thus, it has become necessary to investigate other possible therapies. In this study, we examined the effects of native and oxidized forms of the sodium salts of eicosapentaenoic, docosahexaenoic, and arachidonic acids on T. vaginalis activity. Eicosapentaenoic acid was the most toxic with 190 and 380 μM causing approximately 90% cell death in Casu2 and ATCC 50142 strains, respectively. In contrast, oxidized eicosapentaenoic acid was the least toxic, requiring > 3 mM to inhibit activity, while low levels (10 μM) were associated with increased parasite density. Mass spectrometric analysis of oxidized eicosapentaenoic acid revealed C20 products containing one to six additional oxygen atoms and various degrees of bond saturation. These results indicate that eicosapentaenoic acid has different effects on T. vaginalis survival, depending on whether it is present in the native or oxidized form. A better understanding of lipid metabolism in T. vaginalis may facilitate the design of synthetic fatty acids that are effective for the treatment of metronidazole-resistant T. vaginalis.

The Arabidopsis thaliana lysophospholipid acyltransferase At1g78690p acylates a variety of lysophospholipids including bis(monoacylglycero)phosphate

When the lysoglycerophospholipid (GPL) acyltransferase At1g78690 from Arabidopsis thaliana is over-expressed in Escherichiacoli a headgroup acylated GPL, acyl phosphatidylglycerol (PG), accumulates despite that in vitro this enzyme catalyzes the transfer of an acyl chain from acyl-CoA to the sn-2 position of 1-acyl phosphatidylethanolamine (PE) or 1-acyl PG to form the sn-1, sn-2, di acyl PE and PG respectively; it does not acylate PG to form acyl PG. To begin to understand why the overexpression of a lyso GPL acyltransferase leads to the accumulation of a headgroup acylated GPL in E. coli we investigated the headgroup specificity of At1g78690. Using membranes prepared from E. coli overexpressing At1g78690, we assessed the ability of At1g78690 to catalyze the transfer of acyl chains from acyl-coenzyme A to a variety of lyso GPL acyl acceptors including lyso-phosphatidic acid (PA), -phosphatidylcholine (PC), -phosphatidylserine (PC), -phosphatidylinositol (PI) and three stereoisoforms of bis(monoacylglycero)phosphate (BMP). The predicted products were formed when lyso PI and lyso PC were used as the acyl acceptor but not with lyso PC or lyso PA. In addition, At1g78690 robustly acylates two BMP isoforms with sn-2 and/or sn-2' hydroxyls in the R-stereoconfiguration, but not the BMP isoform with the sn-2 and sn-2' hydroxyls in the S-stereoconfiguration. This strongly suggests that At1g78690 is stereoselective for hydroxyls with R-stereochemistry. In addition, this robust acylation of BMPs by At1g78690, which yields acyl PG like molecules, may explain the mechanism by which At1g78690 so strikingly alters the lipid composition of E. coli.

Mitochondria-derived organelles in the diplomonad fish parasite Spironucleus vortens

In some eukaryotes, mitochondria have become modified during evolution to yield derived organelles (MDOs) of a similar size (hydrogenosomes), or extremely reduced to produce tiny cellular vesicles (mitosomes). The current study provides evidence for the presence of MDOs in the highly infectious fish pathogen Spironucleus vortens, an organism that produces H₂ and is shown here to have no detectable cytochromes. Transmission electron microscopy (TEM) reveals that S. vortens trophozoites contain electron-dense, membranous structures sometimes with an electron-dense core (200 nm-1 μm), resembling the hydrogenosomes previously described in other protists from habitats deficient in O₂. Confocal microscopy establishes that these organelles exhibit autofluorescence emission spectra similar to flavoprotein constituents previously described for mitochondria and also present in hydrogenosomes. These organelles possess a membrane potential and are labelled by a fluorescently labeled antibody against Fe-hydrogenase from Blastocystis hominis. Heterologous antibodies raised to mitochondrial proteins frataxin and Isu1, also exhibit a discrete punctate pattern of localization in S. vortens; however these labelled structures are distinctly smaller (90-150 nm) than hydrogenosomes as observed previously in other organisms. TEM confirms the presence of double-membrane bounded organelles of this smaller size. In addition, strong background immunostaining occurs in the cytosol for frataxin and Isu1, and labelling by anti-ferredoxin antibody is generally distributed and not specifically localized except for at the anterior polar region. This suggests that some of the functions traditionally attributed to such MDOs may also occur elsewhere. The specialized parasitic life-style of S. vortens may necessitate more complex intracellular compartmentation of redox reactions than previously recognized. Control of infection requires biochemical characterization of redox-related organelles.

The evolution of cardiolipin biosynthesis and maturation pathways and its implications for the evolution of eukaryotes

Background

Cardiolipin (CL) is an important component in mitochondrial inner and bacterial membranes. Its appearance in these two biomembranes has been considered as evidence of the endosymbiotic origin of mitochondria. But CL was reported to be synthesized through two distinct enzymes--CLS_cap and CLS_pld in eukaryotes and bacteria. Therefore, how the CL biosynthesis pathway evolved is an interesting question.

Results

Phylogenetic distribution investigation of CL synthase (CLS) showed: most bacteria have CLS_pld pathway, but in partial bacteria including proteobacteria and actinobacteria CLS_cap pathway has already appeared; in eukaryotes, Supergroup Opisthokonta and Archaeplastida, and Subgroup Stramenopiles, which all contain multicellular organisms, possess CLS_cap pathway, while Supergroup Amoebozoa and Excavata and Subgroup Alveolata, which all consist exclusively of unicellular eukaryotes, bear CLS_pld pathway; amitochondriate protists in any supergroups have neither. Phylogenetic analysis indicated the CLS_cap in eukaryotes have the closest relationship with those of alpha proteobacteria, while the CLS_pld in eukaryotes share a common ancestor but have no close correlation with those of any particular bacteria.

Conclusions

The first eukaryote common ancestor (FECA) inherited the CLS_pld from its bacterial ancestor (e. g. the bacterial partner according to any of the hypotheses about eukaryote evolution); later, when the FECA evolved into the last eukaryote common ancestor (LECA), the endosymbiotic mitochondria (alpha proteobacteria) brought in CLS_cap, and then in some LECA individuals the CLS_cap substituted the CLS_pld, and these LECAs would evolve into the protist lineages from which multicellular eukaryotes could arise, while in the other LECAs the CLS_pld was retained and the CLS_cap was lost, and these LECAs would evolve into the protist lineages possessing CLS_pld. Besides, our work indicated CL maturation pathway arose after the emergence of eukaryotes probably through mechanisms such as duplication of other genes, and gene duplication and loss occurred frequently at different lineage levels, increasing the pathway diversity probably to fit the complicated cellular process in various cells. Our work also implies the classification putting Stramenopiles and Alveolata together to form Chromalveolata may be unreasonable; the absence of CL synthesis and maturation pathways in amitochondriate protists is most probably due to secondary loss.