Single eubacterial origin of eukaryotic sulfide:quinone oxidoreductase,a mitochondrial enzyme conserved from the early evolution of eukaryotes during anoxic and sulfidic times

Mitochondria occur as aerobic, facultatively anaerobic, and, in the case of hydrogenosomes, strictly anaerobic forms. This physiological diversity of mitochondrial oxygen requirement is paralleled by that of free-living alpha-proteobacteria, the group of eubacteria from which mitochondria arose, many of which are facultative anaerobes. Although ATP synthesis in mitochondria usually involves the oxidation of reduced carbon compounds, many alpha-proteobacteria and some mitochondria are known to use sulfide (H2S) as an electron donor for the respiratory chain and its associated ATP synthesis. In many eubacteria, the oxidation of sulfide involves the enzyme sulfide:quinone oxidoreductase (SQR). Nuclear-encoded homologs of SQR are found in several eukaryotic genomes. Here we show that eukaryotic SQR genes characterized to date can be traced to a single acquisition from a eubacterial donor in the common ancestor of animals and fungi. Yet, SQR is not a well-conserved protein, and our analyses suggest that the SQR gene has furthermore undergone some lateral transfer among prokaryotes during evolution, leaving the precise eubacterial lineage from which eukaryotes obtained their SQR difficult to discern with phylogenetic methods. Newer geochemical data and microfossil evidence indicate that major phases of early eukaryotic diversification occurred during a period of the Earth's history from 1 to 2 billion years before present in which the subsurface ocean waters contained almost no oxygen but contained high concentrations of sulfide, suggesting that the ability to deal with sulfide was essential for prokaryotes and eukaryotes during that time. Notwithstanding poor resolution in deep SQR phylogeny and lack of a specifically alpha-protebacterial branch for the eukaryotic enzyme on the basis of current lineage sampling, a single eubacterial origin of eukaryotic SQR and the evident need of ancient eukaryotes to deal with sulfide, a process today germane to mitochondrial quinone reduction, are compatible with the view that eukaryotic SQR was an acquisition from the mitochondrial endosymbiont.     

Differences in the methyl ester distribution of homogalacturonans from near-isogenic wheat lines resistant and susceptible to the wheat stem rust fungus

Plants possess an efficient nonself surveillance system triggering induced disease resistance mechanisms upon molecular recognition of microbial invaders. Successful pathogens have evolved strategies to evade or counteract these mechanisms, e.g., by the generation of suppressors. Pectic fragments produced during host cell wall degradation can act as endogenous suppressors of the hypersensitive response in wheat leaves. We have isolated and characterized homogalacturonans from cell walls of two wheat cultivars susceptible to the stem rust fungus, Puccinia graminis f. sp. tritici, namely cvs. Prelude and Marquis, and from near-isogenic lines of both cultivars containing the Sr5-gene for hypersensitive rust resistance. Two independent approaches were used to compare their methyl esterification: i) immunochemistry using the monoclonal antibodies JIM5, JIM7, PAM1, and LM7 and ii) chromatography of oligogalacturonides representing stretches of contiguous nonmethyl-esterified GalA residues. The results clearly indicate a significant difference in the homogalacturonans from susceptible and resistant wheat lines. The difference can best be explained by assuming a nonrandom and more blockwise distribution of the methyl esters in the homogalacturonans of susceptible wheat cultivars as compared with a presumably more random distribution in the near-isogenic resistant lines. Possible consequences of this difference for the enzymatic generation of endogenous suppressors are discussed.     

HIV-1 and its transmembrane protein gp41 bind to different Candida species modulating adhesion

Oral candidiasis in HIV-1-infected individuals is widely believed to be triggered by the acquired T-lymphocyte immunodeficiency. Recently, binding of the HIV-1 envelope protein gp160 and its subunit gp41, and also of the whole virus itself, to Candida albicans has been shown. The present study shows that, in addition to C. albicans, HIV-1 gp41 also binds to yeast and hyphal forms of Candida dubliniensis, a species which is closely related to C. albicans, and to Candida tropicalis but not to Candida krusei, Candida glabrata or Saccharomyces cerevisiae. The previous finding that gp41 binding to C. albicans augments fungal virulence in vitro is supported by the observation that the yeast showed an enhanced adhesion to HIV-infected H9 cells in comparison to uninfected cells. In line with these results soluble gp41 itself reduced binding of C. albicans to both endothelial and epithelial cell lines, confirming a dominant role of the gp41 binding moiety on the surface of Candida for adhesion. Surface-associated secreted aspartic proteinases (Saps) play an important role in candidial adhesion, but are not likely to be involved in the interaction as gp41 binding to the C. albicans parental wild-type strain was comparable to that of three different isogenic Sap deletion mutants. Furthermore, gp41 binding to the yeast killer toxin-susceptible C. albicans strain 10S was not inhibitable by an anti-YKT receptor antibody. In conclusion, HIV-1 interacts with different clinically important Candida spp., and may thereby affect the outcome of the respective fungal infection.     

Interaction of sertraline with Candida species selectively attenuates fungal virulence in vitro

This study investigated whether the interaction between isolates of Candida albicans (n=7), Candida parapsilosis (n=3), Candida krusei (n=2), Candida dubliniensis (n=1) and sertraline, a typical selective serotonin reuptake inhibitor, alters candidal virulence. Sertraline treatment of Candida spp. significantly (P<0.05) affected hyphal elongation, phospholipase activity, production of secreted aspartyl proteinases and fungal viability. In addition, monocyte-derived macrophages (MDMs) treated with sertraline reduced inhibition of blastoconidia germination in comparison to MDMs alone. In conclusion, our findings suggest that the interaction between sertraline and Candida spp. may also diminish the virulence properties of this fungal pathogen in vivo.     

Bone-targeted 2,6,9-trisubstituted purines: novel inhibitors of Src tyrosine kinase for the treatment of bone diseases

Novel bone-targeted 2,6,9-trisubstituted purine template-based inhibitors of Src tyrosine kinase are described. Drug design studies of known purine compounds revealed that both positions-2 and -6 were suitable for incorporating bone-seeking moieties. A variety of bone-targeting groups with different affinity to hydroxyapatite were utilized in the study. Compound 3d was determined to be a potent Src inhibitor and was quite selective against a panel of other protein kinases.     

Effect of methylation on the stability and solvation free energy of amylose and cellulose fragments: a molecular dynamics study

Molecular dynamics (MD) simulations were used to study the stability and solvation of amylose and cellulose fragments. The recently developed gromos carbohydrate force field was further tested by simulating maltose, cellobiose, and maltoheptaose. The MD simulations reproduced fairly well the favorable conformations of disaccharides defined by the torsional angles related with the glycosidic bond and the radius gyration of maltoheptaose. The effects of methylation at different hydroxyl groups on the stability of amylose and cellulose fragments were investigated. The methylations of O-2 and O-3 reduce the stability of a single helix more than methylation at O-6, while the latter reduces the stability of a double helix more. Solvation free-energy differences between the unsubstituted amylose and cellulose fragments and the methylated species were studied using the single-step perturbation method. It was found that methylation at O-2 has the biggest effect, in agreement with experiment.     

Postfusional control of quantal current shape

Whether glutamate is released rapidly, in an all-or-none manner, or more slowly, in a regulated manner, is a matter of debate. We analyzed the time course of excitatory postsynaptic currents (EPSCs) at glutamatergic neuromuscular junctions of Drosophila and found that the decay phase of EPSCs was protracted to a variable extent. The protraction was more pronounced in evoked and spontaneous quantal EPSCs than in action potential-evoked multiquantal EPSCs; reduced in quantal EPSCs from endophilin null mutants, which maintain release via kiss-and-run; and dependent on synaptotagmin isoform, calcium, and protein phosphorylation. Our data indicate that glutamate is released from individual synaptic vesicles for milliseconds through a fusion pore. Quantal glutamate discharge time course depends on presynaptic calcium inflow and the molecular composition of the release machinery.     

A comparative view on sex determination in medaka

In fish, an amazing variety of sex determination mechanisms are known, ranging from hermaphroditism to gonochorism and from environmental to genetic sex determination. This makes fish especially suited for studying sex determination from the evolutionary point of view. In several fish groups, different sex determination mechanisms are found in closely related species, and evolution of this process is still ongoing in recent organisms. The medaka (Oryzias latipes) has an XY-XX genetic sex determination system. The Y-chromosome in this species is at an early stage of evolution. The molecular differences between X and Y are only very subtle and the Y-specific segment is very small. The sex-determining region has accumulated duplicated sequences from elsewhere in the genome, leading to recombinational isolation. The region contains a candidate for the male sex-determining gene named dmrt1bY. This gene arose through duplication of an autosomal chromosome fragment of linkage group 9. While all other genes degenerated, dmrt1bY is the only functional gene in the Y-specific region. The duplication leading to dmrt1bY occurred recently during evolution of the genus Oryzias. This suggests that different genes might be the master sex-determining gene in other fish.