Biosynthesis of lipid-linked oligosaccharides in yeast: the ALG3 gene encodes the Dol-P-Man:Man5GlcNAc2-PP-Dol mannosyltransferase

The formation of N-glycosidic linkages of glycoproteins involves the ordered assembly of the common Glc3Man9GlcNAc2 core-oligosaccharide on the lipid carrier dolichyl pyrophosphate. Whereas early mannosylation steps occur on the cytoplasmic side of the endoplasmic reticulum with GDP-Man as donor, the final reactions from Man5GlcNAc2-PP-Dol to Man9GlcNAc2-PP-Dol on the lumenal side use Dol-P-Man. We have investigated these later stages in vitro using a detergent-solubilized enzyme extract from yeast membranes. Mannosyltransfer from Dol-P-Man to [3H]Man5GlcNAc2-PP-Dol with formation of all intermediates up to Man9GlcNAc2-PP-Dol occured in a rapid, time- and protein-dependent fashion. We find that the initial reaction from Man5GlcNAc2-PP-Dol to Man6GlcNAc2-PP-Dol is independent of metal ions, but further elongations need Mn2+ that can be partly replaced by Mg2+ or Ca2+. Zn2+ or Cd2+ ions were found to inhibit formation of Man(7-9)GlcNAc2-PP-Dol, but do not affect synthesis of Man6GlcNAc2-PP-Dol. Extension did not occur when the acceptor was added as a free Man5GlcNAc2 oligosaccharide or when GDP-Man was used as mannosyl donor. The alg3 mutant was described to accumulate Man5GlcNAc2-PP-Dol. We expressed a functional active HA-epitope tagged ALG3 fusion and succeeded to selectively immunoprecipitate the Dol-P-Man:Man5GlcNAc2-PP-Dol mannosyltransferase activity from the other enzymes of the detergent extract involved in the subsequent mannosylation reactions. This demonstrates that Alg3p represents the mannosyltransferase itself and not an accessory protein involved in the reaction.     

SERPIN regulation of factor XIa. The novel observation that protease nexin 1 in the presence of heparin is a more potent inhibitor of factor XIa than C1 inhibitor

In the present studies we have made the novel observation that protease nexin 1 (PN1), a member of the serine protease inhibitor (SERPIN) superfamily, is a potent inhibitor of the blood coagulation Factor XIa (FXIa). The inhibitory complexes formed between PN1 and FXIa are stable when subjected to reducing agents, SDS, and boiling, a characteristic of the acyl linkage formed between SERPINs and their cognate proteases. Using a sensitive fluorescence-quenched peptide substrate, the K(assoc) of PN1 for FXIa was determined to be 7.9 x 10(4) m(-)(1) s(-)(1) in the absence of heparin. In the presence of heparin, this rate was accelerated to 1.7 x 10(6), M(-)(1) s(-)(1), making PN1 a far better inhibitor of FXIa than C1 inhibitor, which is the only other SERPIN known to significantly inhibit FXIa. FXIa-PN1 complexes are shown to be internalized and degraded by human fibroblasts, most likely via the low density lipoprotein receptor-related protein (LRP), since degradation was strongly inhibited by the LRP agonist, receptor-associated protein. Since FXIa proteolytically modifies the amyloid precursor protein, this observation may suggest an accessory role for PN1 in the pathobiogenesis of Alzheimer's disease.     

Social Isolation Shortens Telomeres in African Grey Parrots (Psittacus erithacus erithacus)

Telomeres, the caps of eukaryotic chromosomes, control chromosome stability and cellular senescence, but aging and exposure to chronic stress are suspected to cause attrition of telomere length. We investigated the effect of social isolation on telomere length in the highly social and intelligent African Grey parrot (Psittacus erithacus erithacus). Our study population consisted of single-housed (n = 26) and pair-housed (n = 19) captive individuals between 0.75 to 45 years of age. Relative telomere length of erythrocyte DNA was measured by quantitative real-time PCR. We found that telomere length declined with age (p<0.001), and socially isolated parrots had significantly shorter telomeres compared to pair-housed birds (p<0.001) – even among birds of similar ages. Our findings provide the first evidence that social isolation affects telomere length, which supports the hypothesis that telomeres provide a biomarker indicating exposure to chronic stress.     

Natural antioxidants attenuate mycolactone toxicity to RAW 264.7 macrophages

Mycobacterium ulcerans produces a macrolide exotoxin, mycolactone which suppresses immune cells activity, is toxic to most cells and the key virulence factor in the pathogenesis of Buruli ulcer disease. Mycolactone is reported to mediate the production of reactive oxygen species in keratinocytes; cells that play critical role in wound healing. Increased levels of reactive oxygen species have been shown to disrupt the well-ordered process of wound repair; hence, the function of wound-healing cells such as macrophages, keratinocytes, and fibroblast could be impaired in the presence of the reactive oxygen species mediator, mycolactone. To ensure regeneration of tissues in chronic ulcers, with proper and timely healing of the wounds, natural antioxidants that can combat the effects of induced reactive oxygen species in wound-healing cells ought to be investigated. Reactive oxygen species activity was determined in mycolactone-treated RAW 264.7 macrophages and the scavenging ability of the antioxidants (ascorbic acid, gallic acid, and green tea kombucha) against mycolactone-induced reactive oxygen species (superoxide anions) was assessed using fluorescein probe (DCF-DA) and nitroblue tetrazolium dye. Cytotoxicity of the antioxidants, mycolactone, and the protective effect of the antioxidants on the cells upon treatment with mycolactone were determined using the Alamar blue assay. The expression levels of endogenous antioxidant enzyme genes (superoxide dismutase, catalase, and glutathione peroxidase) in response to mycolactone-mediated reactive oxygen species were determined using RT-qPCR. Mycolactone induced the production of reactive oxygen species in RAW 264.7 macrophages, and the resulting superoxide anions were scavenged by some of the antioxidants. The selected endogenous antioxidant enzyme genes in the macrophages were upregulated in the presence of the antioxidants and mycolactone. The exogenously supplied ascorbic acid and green tea kombucha offered moderate protection to the macrophages against the toxicity of mycolactone. We conclude that the results provide insights into alternate and adjunct therapeutic approaches in Buruli ulcer treatment, which could significantly attenuate the toxicity of the pathogenic factor; mycolactone.     

The Probability Density Functions of the Contingency Coefficients,defined by KRAMER and PEARSON,in a 2-Dimensional Frequency Distribution of Grouped Bivariate Normal Variables. I

Two general measures for the degree of association in a contingency table are the contingency coefficients defined by PEARSON and KRAMER. In the case of a standardized bivariate normal distribution with correlation coefficient of the variables, whose realizations constitute the rows and columns of the table, the density functions of the two listed association measures are derived.     

Beitrag zur Standortcharakteristik verschiedener Grünland-Pflanzengesellschaften

Ohne Zusammenfassung Prof. Dr. N. Knauer—Abt. Grünlandwirtschaft und Futterbau im Institut für Pflanzenbau und Pflanzenzüchtung der Christian-Albrechts-Universit?t Kiel 23 KIEL, Olshausenstr. 40–60.