Reversible inhibition of mammalian glutamine synthetase by tyrosine nitration

The effect of tyrosine nitration on mammalian GS activity and stability was studied in vitro. Peroxynitrite at a concentration of 5 micro mol/l produced tyrosine nitration and inactivation of GS, whereas 50 micro mol/l peroxynitrite additionally increased S-nitrosylation and carbonylation and degradation of GS by the 20S proteasome. (-)Epicatechin completely prevented both, tyrosine nitration and inactivation of GS by peroxynitrite (5 micro mol/l). Further, a putative "denitrase" activity restored the activity of peroxynitrite (5 micro mol/l)-treated GS. The data point to a potential regulation of GS activity by a reversible tyrosine nitration. High levels of oxidative stress may irreversibly damage and predispose the enzyme to proteasomal degradation.     

The genotype specific competitive ability does not correlate with infection in natural Daphnia magna populations

Background

Different evolutionary hypotheses predict a correlation between the fitness of a genotype in the absence of infection and the likelihood to become infected. The cost of resistance hypothesis predicts that resistant genotypes pay a cost of being resistant and are less fit in the absence of parasites. The inbreeding-infection hypothesis predicts that the susceptible individuals are less fit due to inbreeding depression.

Methods and Results

Here we tested if a host''s natural infection status was associated with its fitness. First, we experimentally confirmed that cured but formerly infected Daphnia magna are genetically more susceptible to reinfections with Octosporea bayeri than naturally uninfected D. magna. We then collected from each of 22 populations both uninfected and infected D. magna genotypes. All were treated against parasites and kept in their asexual phase. We estimated their relative fitness in an experiment against a tester genotype and in another experiment in direct competition. Consistently, we found no difference in competitive abilities between uninfected and cured but formerly infected genotypes. This was the case both in the presence as well as in the absence of sympatric parasites during the competition trials.

Conclusions

Our data do not support the inbreeding-infection hypothesis. They also do not support a cost of resistance, however ignoring other parasite strains or parasite species. We suggest as a possible explanation for our results that resistance genes might segregate largely independently of other fitness associated genes in this system.     

Microbial mats and physicochemistry in a saltern in the Bretagne (France) and in a laboratory scale saltern model

Abstract A saltern near La Baule (Bretagne, France) was remodeled in a programmable temperature and humidity controlled walk-in environmental chamber resembling the characteristics of the original saltern. The saltern showed different types of microbial mats predominantly composed of algae, oxy- and anoxyphotobacteria, and associated chemoorganotrophic bacteria, fungi and animals. Well-developed microbial mats were found up to a salinity of 10% during the three or four months in summer when salinity gradients and NaCl precipitation were established. The main phototrophic organisms were diatoms, the cyanobacteria Aphanothece, Microcoleus, Spirulina , and Oscillatoria , and Chromatiaceae. At higher salinity, Halobacterium sp., diatoms, and Dunaliella were dominant. Typical microbial mats and saltern-typical invertebrate, algal and bacterial species also developed in the saltern model, building up a stable community. The ionic composition of the brines and physicochemical parameters were similar to those determined for the original saltern. Different photosynthetic organisms, e.g. a filamentous purple bacterium and a hypersaline Chloroflexus -like organism, could be enriched within the microbial mats by changing the light regime.     

Tailoring host immune responses to Listeria by manipulation of virulence genes -- the interface between innate and acquired immunity

Although attenuated strains of microbial pathogens have triggered vaccine development from its origin, the role of virulence factors in determining host immunity has remained largely unexplored. Using the murine listeriosis model, we investigated whether the induction and expansion of protective and inflammatory T cell responses may be modified by selective manipulation of virulence genes. We intentionally deleted specific genes of Listeria monocytogenes, including those encoding the positive regulatory factor (prfA), hemolysin (hly), the actin nucleator (actA), and phospholipase B (plcB). The resulting strains showed decisive differences in their immunogenic properties. In particular, we identified a double-deletion mutant that retained Listeria's profound ability to induce protective CD8(+) T cells, but that is strongly attenuated and exhibits a significantly reduced ability to induce CD4(+) T cell-mediated inflammation. We conclude that this mutant, L. monocytogenes DeltaactADeltaplcB, is at present the most promising mutant for a bacterial vaccine vector and is able to safely induce potent CD8(+) T cell-mediated immunity.     

Karyotype analysis in Hyacinthella dalmatica (Hyacinthaceae) reveals vertebrate-type telomere repeats at the chromosome ends.

Chromosome analysis of three different populations of Hyacinthella dalmatica (Lallem.) Trinajsti?, an endemic species of the coastal region of southeastern Europe, showed a unique chromosome number, 2n = 2x = 20, and bimodal karyotype with one large and nine smaller pairs of chromosomes. Staining with fluorochromes CMA3 (chromomycin A3) and DAPI (4,6-diamidino-2-phenylindole) revealed heterochromatic regions associated with NORs, centromeres, and several interstitial heterochromatic bands on the longest chromosome pair. Double-target FISH with two ribosomal DNA probes revealed one locus of 5S rRNA genes in the pericentromeric region of chromosome pair 3 and one locus of 18S-5.8S-26S rRNA genes on the short arm of chromosome pair 4 in all plants and populations analyzed. Southern hybridization analysis and FISH experiments demonstrated that the distal ends of H. dalmatica chromosomes contain the vertebrate telomere (5'-TTAGGG-3') repeat type rather than the Arabidopsis (5'-TTTAGGG-3') heptamer, and so suggest that this Asparagales species along with Aloe and Othocallis contains the vertebrate-type telomere repeat.     

Nortropinyl-arylsulfonylureas as novel, reversible inhibitors of human steroid sulfatase

Steroid sulfatase (STS) has emerged as an attractive target for a range of estrogen- and androgen-dependent diseases. Searching for novel chemotypes as STS inhibitors, we identified nortropinyl-arylsulfonylurea 3 as a hit from high-throughput screening. A series of analogues was prepared in order to explore the essential structural elements for STS inhibition, and first structure-activity relationships were established. Mechanistic investigations revealed that the compounds are reversible, competitive inhibitors of STS.     

Furanonaphthoquinones,atraric acid and a benzofuran from the stem barks of Newbouldia laevis

The series of naturally occurring furanonaphthoquinones is extended by identification of the derivatives 2-(1'-methylethenyl)-5-hydroxynaphtho[2,3-b]furan-4,9-dione and 2-(1'-methylethenyl)-7-hydroxynaphtho[2,3-b]furan-4,9-dione. They are accompanied in the stem barks of Newbouldia laevis by the known analogues 5-hydroxy-dehydro-iso-alpha-lapachone, 2-acetyl-5-hydroxynaphtho[2,3-b]furan-4,9-dione and 2-(1'-methylethenyl)naphtho[2,3-b]furan-4,9-dione along with the rare atraric acid and the new 2-(1'-methylethenyl)-6-hydroxy-2,3-dihydrobenzofuran. The structures of these compounds were established from spectroscopic studies.     

Crystal structures and enzymatic properties of three formyltransferases from archaea: environmental adaptation and evolutionary relationship

Formyltransferase catalyzes the reversible formation of formylmethanofuran from N(5)-formyltetrahydromethanopterin and methanofuran, a reaction involved in the C1 metabolism of methanogenic and sulfate-reducing archaea. The crystal structure of the homotetrameric enzyme from Methanopyrus kandleri (growth temperature optimum 98 degrees C) has recently been solved at 1.65 A resolution. We report here the crystal structures of the formyltransferase from Methanosarcina barkeri (growth temperature optimum 37 degrees C) and from Archaeoglobus fulgidus (growth temperature optimum 83 degrees C) at 1.9 A and 2.0 A resolution, respectively. Comparison of the structures of the three enzymes revealed very similar folds. The most striking difference found was the negative surface charge, which was -32 for the M. kandleri enzyme, only -8 for the M. barkeri enzyme, and -11 for the A. fulgidus enzyme. The hydrophobic surface fraction was 50% for the M. kandleri enzyme, 56% for the M. barkeri enzyme, and 57% for the A. fulgidus enzyme. These differences most likely reflect the adaptation of the enzyme to different cytoplasmic concentrations of potassium cyclic 2,3-diphosphoglycerate, which are very high in M. kandleri (>1 M) and relatively low in M. barkeri and A. fulgidus. Formyltransferase is in a monomer/dimer/tetramer equilibrium that is dependent on the salt concentration. Only the dimers and tetramers are active, and only the tetramers are thermostable. The enzyme from M. kandleri is a tetramer, which is active and thermostable only at high concentrations of potassium phosphate (>1 M) or potassium cyclic 2,3-diphosphoglycerate. Conversely, the enzyme from M. barkeri and A. fulgidus already showed these properties, activity and stability, at much lower concentrations of these strong salting-out salts.     

Occurrence and settlement of the common shipworm Teredo navalis (Bivalvia: Teredinidae) in Bremerhaven harbours, northern Germany

The shipworm Teredo navalis L. is a xylophagous bivalve mollusc (Bivalvia: Teredinidae) with a long record of being very destructive to wooden ships and harbour buildings. It has been reported from numerous sites at the coasts of both the North and Baltic Seas since the eighteenth century. Here, we document for the first time the occurrence of live adult T. navalis in the harbours of Bremerhaven (Weser estuary, northern Germany). From August to December 1998, various wooden structures (fir floating fenders and pier posts, oak piles) from seven stations in different docks of two harbours (überseehafen, Fischereihafen) were investigated for the presence and density of live specimens and burrows of T. navalis. The settlement of larval shipworms was studied by exposing experimental fir panels 0.06 m² in size at 20 stations at water depths between 1 and 2 m for periods of 4 months between July and November. In addition, hydrographic profiles (0–8 m water depth) were obtained at 17 stations in five docks once every month from August to December. Live adult shipworms were found in both fir floating fenders and oak piles at four stations. The largest specimen found was 250 mm long. Shipworm burrows were detected at five stations in almost every wooden structure investigated but their abundances differed significantly: Maximum values were >10,000 m^–2 in fir floating fenders, 4,600 m^–2 in oak piles and 200 m^–2 in fir pier posts. Actual shipworm infestation was detected at three of 16 stations in the exposed fir panels (1–3 burrow holes per panel). Water temperatures and salinities varied considerably during the 4-month investigation period. Temperatures decreased from 19.9°C in August to 0.7°C in December. Salinities ranged from 17.6 in August to 1.1 in November, but only at two lock stations during November and December did value drop below 5, which is regarded as the lethal limit for the larvae of this euryhaline teredinid species. We conclude that T. navalis encounters favourable conditions for growth and reproduction in the harbours of Bremerhaven, at least during summer and autumn, and is a common element of the harbour ecosystem. Therefore, a persistent infestation of all wooden structures after a relatively short period of time seems to be highly probable. Electronic Publication