Integrin αXβ2 Is a Leukocyte Receptor for Candida albicans and Is Essential for Protection against Fungal Infections

The opportunistic fungus Candida albicans is one of the leading causes of infections in immunocompromised patients, and innate immunity provides a principal mechanism for protection from the pathogen. In the present work, the role of integrin α(X)β(2) in the pathogenesis of fungal infection was assessed. Both purified α(X)β(2) and α(X)β(2)-expressing human epithelial kidney 293 cells recognized and bound to the fungal hyphae of SC5314 strain of C. albicans but not to the yeast form or to hyphae of a strain deficient in the fungal mannoprotein, Pra1. The binding of the integrin to the fungus was inhibited by β-glucans but not by mannans, implicating a lectin-like activity in recognition but distinct in specificity from that of α(M)β(2). Mice deficient in α(X)β(2) were more prone to systemic infection with the LD(50) fungal inoculum decreasing 3-fold in α(X)β(2)-deficient mice compared with wild-type mice. After challenging i.v. with 1.5 × 10(4) cell/g, 60% of control C57BL/6 mice died within 14 d compared with 100% mortality of α(X)β(2)-deficient mice within 9 d. Organs taken from α(X)β(2)-deficient mice 16 h postinfection revealed a 10-fold increase in fungal invasion into the brain and a 2-fold increase into the liver. These data indicate that α(X)β(2) is important for protection against systemic C. albicans infections and macrophage subsets in the liver, Kupffer cells, and in the brain, microglial cells use α(X)β(2) to control fungal invasion.     

Nucleotide exchange via local protein unfolding--structure of Rab8 in complex with MSS4

Rab GTPases function as essential regulators of vesicle transport in eukaryotic cells. MSS4 was shown to stimulate nucleotide exchange on Rab proteins associated with the exocytic pathway and to have nucleotide-free-Rab chaperone activity. A detailed kinetic analysis of MSS4 interaction with Rab8 showed that MSS4 is a relatively slow exchange factor that forms a long-lived nucleotide-free complex with RabGTPase. In contrast to other characterized exchange factor-GTPase complexes, MSS4:Rab8 complex binds GTP faster than GDP, but still ca. 3 orders of magnitude more slowly than comparable complexes. The crystal structure of the nucleotide-free MSS4:Rab8 complex revealed that MSS4 binds to the Switch I and interswitch regions of Rab8, forming an intermolecular beta-sheet. Complex formation results in dramatic structural changes of the Rab8 molecule, leading to unfolding of the nucleotide-binding site and surrounding structural elements, facilitating nucleotide release and slowing its rebinding. Coupling of nucleotide exchange activity to a cycle of GTPase unfolding and refolding represents a novel nucleotide exchange mechanism.     

Distribution of introns in the mitochondrial gene nad1 in land plants: phylogenetic and molecular evolutionary implications

Forty-six species of diverse land plants were investigated by sequencing for their intron content in the mitochondrial gene nad1. A total of seven introns, all belonging to group II, were found, and two were newly discovered in this study. All 13 liverworts examined contain no intron, the same condition as in green algae. Mosses and hornworts, however, share one intron by themselves and another one with vascular plants. These intron distribution patterns are consistent with the hypothesis that liverworts represent the basal-most land plants and that the two introns were gained in the common ancestor of mosses-hornworts-vascular plants after liverworts had diverged. Hornworts also possess a unique intron of their own. A fourth intron was found only in Equisetum L., Marattiaceae, Ophioglossum L., Osmunda L., Asplenium L., and Adiantum L., and was likely acquired in their common ancestor, which supports the monophyly of moniliformopses. Three introns that were previously characterized in angiosperms and a few pteridophytes are now all extended to lycopods, and were likely gained in the common ancestor of vascular plants. Phylogenetic analyses of the intron sequences recovered topologies mirroring those of the plants, suggesting that the introns have all been vertically inherited. All seven nad1 group II introns show broad phylogenetic distribution patterns, with the narrowest being in moniliformopses and hornworts, lineages that date back to at least the Devonian (345 million years ago) and Silurian (435 million years ago), respectively. Hence, these introns must have invaded the genes via ancient transpositional events during the early stage of land plant evolution. Potentially heavy RNA editing was observed in nad1 of Haplomitrium Dedecek, Takakia Hatt. & Inoue, hornworts, Isoetes L., Ophioglossum, and Asplenium. A new nomenclature is proposed for group II introns.     

Trematodes from Antarctic teleost fishes off Argentine Islands,West Antarctica: molecular and morphological data

Systematic Parasitology - In 2014–2015 and 2019–2021, teleost fishes off Galindez Island (Antarctic Peninsula) were examined for trematodes. Combined morphological and molecular...     

A role of phosphorylase in the potato minituber function under altered gravity

The goal of our work was a role of phosphorylase (EC. 2.4.1.1) in starch accumulation in plastids of storage parenchyma cells in potato minitubers forming under clinorotation. An increased enzyme activity under the influence of simulated microgravity has been revealed by using the biochemical and electron cytochemical methods. The obtained results suggest the correlation between an increase in phosphorylase activity and acceleration growth rate and senescence of plant storage organs in microgravity.     

Influence of Sambucus nigra bark lectin on cell DNA under different in vitro conditions

The biological activity of Sambucus nigra bark lectin on Chinese hamster cells in vitro was investigated by comet-assay and cytotoxicity testing. Mitogenic properties at the concentrations 0.063-0.25 microg/ml (but not higher) were found, and the induction of DNA breaks at concentrations 0.5 microg/ml and higher is demonstrated. S. nigra bark lectin at mitogenic concentrations decreased the level of nickel-induced DNA damage. The character and mechanism of this lectin protective activity was probably related to the induction of DNA reparation in the cells, decreasing nickel uptake in cells, and non-specific binding of nickel ions by protein molecules.     

Deubiquitinase inhibition by WP1130 leads to ULK1 aggregation and blockade of autophagy

Autophagy represents an intracellular degradation process which is involved in both regular cell homeostasis and disease settings. In recent years, the molecular machinery governing this process has been elucidated. The ULK1 kinase complex consisting of the serine/threonine protein kinase ULK1 and the adapter proteins ATG13, RB1CC1, and ATG101, is centrally involved in the regulation of autophagy initiation. This complex is in turn regulated by the activity of different nutrient- or energy-sensing kinases, including MTOR, AMPK, and AKT. However, next to phosphorylation processes it has been suggested that ubiquitination of ULK1 positively influences ULK1 function. Here we report that the inhibition of deubiquitinases by the compound WP1130 leads to increased ULK1 ubiquitination, the transfer of ULK1 to aggresomes, and the inhibition of ULK1 activity. Additionally, WP1130 can block the autophagic flux. Thus, treatment with WP1130 might represent an efficient tool to inhibit the autophagy-initiating ULK1 complex and autophagy.     

Phytochelatin synthase, a dipeptidyltransferase that undergoes multisite acylation with gamma-glutamylcysteine during catalysis: stoichiometric and site-directed mutagenic analysis of arabidopsis thaliana PCS1-catalyzed phytochelatin synthesis

Phytochelatin (PC) synthase has been assumed to be a gamma-glutamylcysteine dipeptidyl transpeptidase (EC 2.3.2.15) and, more recently, as exemplified by analyses of the immunopurified recombinant enzyme from Arabidopsis thaliana (AtPCS1-FLAG), has been shown to catalyze a PC synthetic reaction with kinetics that approximates a bisubstrate-substituted enzyme mechanism in which millimolar concentrations of free GSH and micromolar concentrations of heavy metal.GSH thiolates (e.g. cadmium.GS(2)) or millimolar concentrations of S-alkylglutathiones serve as cosubstrates. Here, we show, by direct analyses of the stoichiometry of AtPCS1-FLAG-catalyzed PC synthesis, the kinetics and stoichiometry of acylation of the enzyme and release of free glycine from gamma-Glu-Cys donors, and the effects of the Cys-to-Ser or -Ala and Ser-to-Ala substitution of conserved residues in the catalytic N-terminal half of the enzyme, that PC synthase is indeed a dipeptidyltransferase that undergoes gamma-Glu-Cys acylation at two sites during catalysis, one of which, in accord with a cysteine protease model, likely corresponds to or is at least tightly coupled with Cys(56). The identity of the second site of enzyme modification remains to be determined, but it is distinguishable from the first Cys(56)-dependent site, which is amenable to gamma-Glu-Cys acylation by free GSH, because its acylation not only depends on the provision of Cd(2+) or GSH with a blocked, S-alkylated thiol group, but is also necessary for net PC synthesis. We conclude that des-Gly-PCs are not generated as an immediate by-product, but rather that the enzyme catalyzes a dipeptidyl transfer reaction in which some of the energy liberated upon cleavage of the Cys-Gly bonds of the gamma-Glu-Cys donors in the first phase of the catalytic cycle is conserved through the formation of a two site-substituted gamma-Glu-Cys acyl-enzyme intermediate whose hydrolysis provides the energy required for the formation of the new peptide bond required for the extension of PC chain length by one gamma-Glu-Cys repeat per catalytic cycle.