<Emphasis Type="Italic">Erysiphe catalpae</Emphasis> and <Emphasis Type="Italic">Erysiphe elevata</Emphasis> in Europe

The recent epidemic spread of the North American powdery mildew Erysiphe elevata in Europe is described and discussed. Since 2002, this plant pathogenic fungus has been collected on Catalpa bignonioides, C. erubescens and C. speciosa in the Czech Republic, Germany, Hungary, Slovakia and Switzerland. The diagnostically important anamorph of E. elevata, so far unknown, is described and illustrated in detail. Type material of Erysiphe catalpae and two specimens of E. catalpae recently collected in Poland have been examined and compared with E. elevata. The anamorph as well as the teleomorph of E. catalpae proved to be easily distinguishable from E. elevata. The supposition that E. catalpae, introduced in Armenia, was based on immature ascomata of E. elevata proved to be wrong. The origin and distribution of E. catalpae are discussed, and a key to powdery mildew fungi on Catalpa spp. in Europe is provided.     

Extracellular cysteines define ectopeptidase (APN, CD13) expression and function

Alanyl aminopeptidase (APN) is a surface-bound metallopeptidase that processes the N-terminals of biologically active peptides such as enkephalins, angiotensins, neurokinins, and cytokines. It exerts profound activity on vital processes such as immune response, cellular growth, and blood pressure control. Inhibition of either APN gene expression or its enzymatic activity severely affects leukocyte growth and function. We show here that oxidoreductase-mediated modulations of the cell surface thiol status affect the enzymatic activity of APN. Additional evidence for the pivotal role of extracellular cysteines in the APN molecule was obtained when substitution of any of these six cysteines caused complete loss of surface expression and enzymatic activity. In contrast, the transmembrane Cys24 appears to have no similar function. Enzymatically inactive cysteine mutants were retained in the endoplasmic reticulum as shown by high-resolution imaging and Endoglycosidase H digestion. In the absence of any crystal-structure data, the demonstration that individual extracellular cysteines contribute to APN expression and function appears to be of particular importance. The data are the first to show thiol-dependent modulation of the activity of a typical surface-bound peptidase at the cell surface, probably reflecting a general regulating mechanism. This may relate to various disease processes such as inflammation or malignant transformation.     

Virulence‐associated protein A from Rhodococcus equi is an intercompartmental pH‐neutralising virulence factor

Professional phagocytic cells such as macrophages are a central part of innate immune defence. They ingest microorganisms into membrane‐bound compartments (phagosomes), which acidify and eventually fuse with lysosomes, exposing their contents to a microbicidal environment. Gram‐positive Rhodococcus equi can cause pneumonia in young foals and in immunocompromised humans. The possession of a virulence plasmid allows them to subvert host defence mechanisms and to multiply in macrophages. Here, we show that the plasmid‐encoded and secreted virulence‐associated protein A (VapA) participates in exclusion of the proton‐pumping vacuolar‐ATPase complex from phagosomes and causes membrane permeabilisation, thus contributing to a pH‐neutral phagosome lumen. Using fluorescence and electron microscopy, we show that VapA is also transferred from phagosomes to lysosomes where it permeabilises the limiting membranes for small ions such as protons. This permeabilisation process is different from that of known membrane pore formers as revealed by experiments with artificial lipid bilayers. We demonstrate that, at 24 hr of infection, virulent R. equi is contained in a vacuole, which is enriched in lysosome material, yet possesses a pH of 7.2 whereas phagosomes containing a vapA deletion mutant have a pH of 5.8 and those with virulence plasmid‐less sister strains have a pH of 5.2. Experimentally neutralising the macrophage endocytic system allows avirulent R. equi to multiply. This observation is mirrored in the fact that virulent and avirulent R. equi multiply well in extracts of purified lysosomes at pH 7.2 but not at pH 5.1. Together these data indicate that the major function of VapA is to generate a pH‐neutral and hence growth‐promoting intracellular niche. VapA represents a new type of Gram‐positive virulence factor by trafficking from one subcellular compartment to another, affecting membrane permeability, excluding proton‐pumping ATPase, and consequently disarming host defences.     

Phosphoenolpyruvate carboxylase in mistletoe leaves: Regulation of gene expression, protein content, and covalent modification

Seasonal changes in the activity of phospho enol pyruvate carboxylase (PEPCase, EC 4.1.1.31), a key enzyme in the interaction of carbohydrate and nitrogen metabolism, were studied in leaves of the C₃ semiparasitic mistletoe, Viscum album, growing on different host trees. Maximum extractable PEPCase activities were higher in leaves of mistletoes growing on Betula pendula and Alnus glutinosa hosts compared with those on the conifers, Abies alba and Larix decidua . Independent of host, maximum extractable PEPCase activities were high in spring and autumn while low in summer. Samples with higher PEPCase activities showed higher amounts of PEPCase protein and higher PEPCase mRNA levels. A curvilinear correlation between leaf total nitrogen content and the maximum extractable PEPCase activity as well as PEPCase mRNA level suggested that nitrogen might affect the activity of PEPCase of mistletoe by up-regulating gene expression. In addition to extractable activity, seasonal changes of the PEPCase activation state, the ratio of activities resulting from limited:non-limited assays, were found, which was correlated to the variation of malate content in leaves of mistletoe. ATP-dependent activation of PEPCase was characterized by an increase in I_0.5( l -malate), indicating that PEPCase of leaves of mistletoes is probably regulated via phosphorylation.     

The pigmentation of human iris influences the uptake and storing of zinc

Age-related macular degeneration (AMD) is more prevalent among the elderly Caucasians than in Africans. A significant association between light iris colour, fundus pigmentation and incidence of AMD is reported, suggesting a possible correlation with melanin pigment. Zinc is known to bind to melanin in pigmented tissues and to enhance antioxidant capacity by function as a cofactor or gene expression factor of antioxidant enzymes in the eye. In this in vitro study, we investigated the uptake and storage of zinc in human irides. Irides of blue and brown human eyes were used. The number of melanocytes was measured. Tissues without any treatment served as controls. The irides were incubated with 100 microM zinc chloride in culture medium for 24 h. Specimens of the tissues were stored for the uptake examination. The remained pieces were further incubated for 3 and 7 d to investigate the storage of zinc. The concentration of zinc was measured by inductively coupled plasma mass spectrometry (ICP-MS). Melanocytes count was significantly higher in the brown tissues (P < 0.0001). Zinc concentration of blue coloured irides after 24 h zinc treatment was close to the controls. We did not observe any significant storing. In contrast, the concentration of zinc in brown irides was significantly increased after 24 h (P < or = 0.01) and remained at a high level for 7 d. The uptake of zinc is likely dependent on the amount of pigmentation in human iris. Therefore, we assume that in patients suffering from AMD the degree of pigmentation of the irides and eventually fundi should be under consideration when the patients are treated with zinc supplementation.