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At least 775 records · Page 43Linked to original sources
PubMed2005

Epstein-Barr virus gp42 is posttranslationally modified to produce soluble gp42 that mediates HLA class II immune evasion.

Epstein-Barr virus (EBV) resides as a persistent infection in human leukocyte antigen (HLA) class II+ B lymphocytes and is associated with a number of malignancies. The EBV lytic-phase protein gp42 serves at least two functions: gp42 acts as the coreceptor for viral entry into B cells and hampers T-cell recognition via HLA class II molecules through steric hindrance of T-cell receptor-class II-peptide interactions. Here, we show that gp42 associates with class II molecules at their various stages of maturation, including immature alphabetaIi heterotrimers and mature alphabeta-peptide complexes. When analyzing the biosynthesis and maturation of gp42 in cells stably expressing the viral protein, we found that gp42 occurs in two forms: a full-length type II membrane protein and a truncated soluble form. Soluble gp42 is generated by proteolytic cleavage in the endoplasmic reticulum and is secreted. Soluble gp42 is sufficient to inhibit HLA class II-restricted antigen presentation to T cells. In an almost pure population of Burkitt's lymphoma cells in the EBV lytic cycle, both transmembrane and soluble forms of gp42 are detected. These results imply that soluble gp42 is generated during EBV lytic infection and could contribute to undetected virus production by mediating evasion from T-cell immunity.

Amino Acid Sequence↗
PubMed2003

Maternal transfer of strain-specific immunity in an invertebrate.

The most celebrated component of the vertebrate immune system is the acquired response in which memory cells established during primary infection enhance the proliferation of antibodies during secondary infection. Additionally, the strength of vertebrate acquired immune responses varies dramatically depending on the infecting pathogen species or on the pathogen genotype within species. Because invertebrates lack the T-cell receptors and Major Histocompatibility Complex (MHC) molecules that mediate vertebrate adaptive immune responses, they are thought to lack adaptive immunity and be relatively unspecific in their interactions with pathogens. With only innate immunity, invertebrate hosts are believed to be nai;ve at each new encounter with pathogens. Nevertheless, some forms of facultative immunity appear to be important in insects; some individuals have enhanced immunity due to population density, and some social insects benefit when their nest-mates have been exposed to a pathogen or pathogen mimic (; see for a predation example.) Here we provide evidence for acquired strain-specific immunity in the crustacean Daphnia magna infected with the pathogenic bacteria Pasteuria ramosa. Specifically, the fitness of hosts was enhanced when challenged with a bacterial strain their mother had experienced relative to cases when mother and offspring were challenged with different strains.

Animals↗
PubMedDate not supplied

Market-oriented health care reforms and policy learning in the Netherlands.

In this article we analyze the evolution of market-oriented health care reforms in the Netherlands. We argue that these reforms can be characterized as policy learning within and between competing policy programs. Policy learning denotes the process by which policy makers and stakeholders deliberately adjust the goals, rules, and techniques of a given policy in response to past experiences and new information. We discern three distinctive periods. During the first period (1988-1994), the prevailing corporatist and etatist policy programs were seriously challenged by the proponents of a new market-oriented program. But when it came to political decision making and implementation, the market-oriented program soon lost its impetus because it was technically too complex and could not provide short-term solutions to meet the urgent need for cost containment. During the second period (1994-2000), the etatist program regained its previously dominant position. In parallel to a strengthening of supply and price controls, however, the government also persevered in creating the technical and institutional preconditions for regulated competition. Moreover, public discontent over waiting lists and the call for more autonomy by individual providers and insurers strengthened the alliance in favor of regulated competition. This led to the revival of the market-oriented program in a 2001 reform plan. We conclude that the odds of these new post-2001 reforms succeeding are substantially higher than in the first period due to the technical and institutional adjustments that have taken place in the past decade.

Capitation Fee↗
PubMed2004

B1-type cyclin-dependent kinases are essential for the formation of stomatal complexes in Arabidopsis thaliana.

Cyclin-dependent kinases (CDKs) are key regulators of the cell cycle. In yeasts, only one CDK is sufficient to drive cells through the cell cycle, whereas higher eukaryotes developed a family of related CDKs. Curiously, plants contain a unique class of CDKs (B-type CDKs), whose function is still unclear. We show that the CDKB1;1 gene of Arabidopsis (Arabidopsis thaliana) is highly expressed in guard cells and stomatal precursor cells of cotyledons, suggesting a prominent role for B-type CDKs in stomatal development. In accordance, transgenic Arabidopsis plants with reduced B-type CDK activity had a decreased stomatal index because of an early block of meristemoid division and inhibition of satellite meristemoid formation. Many aberrant stomatal cells were observed, all of them blocked in the G2 phase of the cell cycle. Although division of stomatal precursors was inhibited, cells still acquired stomatal identity, illustrating that stomatal cell differentiation is independent of cellular and nuclear division.

Arabidopsis↗
PubMed2005

Concepts in nuclear architecture.

Genomes are defined by their primary sequence. The functional properties of genomes, however, are determined by far more complex mechanisms and depend on multiple layers of regulatory control processes. A key emerging contributor to genome function is the architectural organization of the cell nucleus. The spatial and temporal behavior of genomes and their regulatory proteins are now being recognized as important, yet still poorly understood, control mechanisms in genome function. Combined cell biological, molecular and computational analysis of architectural aspects of genome function has added a further dimension to the investigation of some of the most fundamental cellular processes including transcription and maintenance of genome integrity. The complete elucidation of the contribution that nuclear architecture makes to gene expression will be required to fully understand physiological processes such as differentiation, development and disease at the cellular level. Here I give an overview of some of the emerging concepts in the study of in vivo genome organization and function.

Animals↗
PubMed1995

Synthesis of (+)-dynemicin A and analogs of wide structural variability: establishment of the absolute configuration of natural dynemicin A.

BACKGROUND: Dynemicin A is an exceedingly potent antitumor antibiotic derived from microbial fermentation that cleaves double-stranded B-form DNA in vitro in the presence of activating factors such as NADPH or glutathione. Because of the structural complexity, high reactivity, and scarcity of natural dynemicin A, it has not been feasible to modify the structure to any significant extent. Previous studies have not determined the absolute configuration of the natural product. RESULTS: A multistep route for the preparation of enantiomerically pure, synthetic dynemicin A was developed. The absolute configuration of natural dynemicin was determined by comparing the synthetic drug with dynemicin A derived from fermentation. The route that was developed is highly convergent, as the result of a late-stage coupling reaction that combines two complex synthetic fragments, and has been shown to provide access to non-natural dynemicins of wide structural variability by modifications of these fragments. In this way, several nonnatural dynemicins, unavailable by any other means, were synthesized and shown to have DNA-cleaving activity in the presence of glutathione or NADPH. CONCLUSIONS: Enantiomerically pure dynemicin A is now available by laboratory synthesis. The natural, (+)-enantiomer of dynemicin A is shown to possess the 2S, 3S, 4S, 7R, 8R configuration. A wide variety of heretofore unavailable, active analogs of dynemicin A have been prepared and are found to produce subtle variations in sequence specificity of DNA cleavage compared to the natural product and, of potentially greater significance, display variations in the efficiency of DNA cleavage as a function of the activating agent.

Anthraquinones↗
PubMed2005

Emergence of W135 meningococcal meningitis in Ghana.

Neisseria meningitidis serogroup W135, well known for a long time as a cause of isolated cases of meningococcal meningitis, has recently increasingly been associated with disease outbreaks of considerable magnitude. Burkina Faso was hit by W135 epidemics in the dry seasons of 2002-2004, but only four W135 meningitis cases were recorded between February 2003 and March 2004 in adjoining Ghana. This reconfirms previous findings that bottlenecks exist in the spreading of new epidemic N. meningitidis clones within the meningitis belt of sub-Saharan Africa. Of the four Ghanaian W135 meningitis patients one died and three survived, of whom one had profound neurosensory hearing loss and speech impairment. All four disease isolates were sensitive to penicillin G, chloramphenicol, ciprofloxacin and cefotaxime and had the multi-locus sequence type (ST) 11, which is the major ST of the ET-37 clonal complex. Pulsed-field gel electrophoresis (PFGE) profiles of the Ghanaian disease isolates and recent epidemic isolates from Burkina Faso were largely identical. We conducted meningococcal colonization surveys in the home communities of three of the patients and in the Kassena Nankana District located at the border to Burkina Faso. W135 carriage rates ranged between 0% and 17.5%. When three consecutive surveys were conducted in the patient community with the highest carrier rate, persistence of W135 colonization over a period of 1 year was observed. Differences in PFGE profiles of carrier isolates taken at different times in the same patient community were indicative of rapid microevolution of the W135 bacteria, emphasizing the need for innovative fine typing methods to reveal the relationship between W135 isolates.

Adolescent↗
PubMed2003

Functional regions of the presynaptic cytomatrix protein bassoon: significance for synaptic targeting and cytomatrix anchoring.

Exocytosis of neurotransmitter from synaptic vesicles is restricted to specialized sites of the presynaptic plasma membrane called active zones. A complex cytomatrix of proteins exclusively assembled at active zones, the CAZ, is thought to form a molecular scaffold that organizes neurotransmitter release sites. Here, we have analyzed synaptic targeting and cytomatrix association of Bassoon, a major scaffolding protein of the CAZ. By combining immunocytochemistry and transfection of cultured hippocampal neurons, we show that the central portion of Bassoon is crucially involved in synaptic targeting and CAZ association. An N-terminal region harbors a distinct capacity for N-myristoylation-dependent targeting to synaptic vesicle clusters, but is not incorporated into the CAZ. Our data provide the first experimental evidence for the existence of distinct functional regions in Bassoon and suggest that a centrally located CAZ targeting function may be complemented by an N-terminal capacity for targeting to membrane-bounded synaptic organelles.

Animals↗
PubMed2003

Interactions between Sec complex and prepro-alpha-factor during posttranslational protein transport into the endoplasmic reticulum.

Posttranslational translocation of prepro-alpha-factor (ppalphaF) across the yeast endoplasmic reticulum membrane begins with the binding of the signal sequence to the Sec complex, a membrane component consisting of the trimeric Sec61p complex and the tetrameric Sec62p/63p complex. We show by photo-cross-linking that the signal sequence is bound directly to a site where it contacts simultaneously Sec61p and Sec62p, suggesting that there is a single signal sequence recognition step. We found no evidence for the simultaneous contact of the signal sequence with two Sec61p molecules. To identify transmembrane segments of Sec61p that line the actual translocation pore, a late translocation intermediate of ppalphaF was generated with photoreactive probes incorporated into the mature portion of the polypeptide. Cross-linking to multiple regions of Sec61p was observed. In contrast to the signal sequence, neighboring positions of the mature portion of ppalphaF had similar interactions with Sec61p. These data suggest that the channel pore is lined by several transmembrane segments, which have no significant affinity for the translocating polypeptide chain.

Biological Transport↗
PubMed2003

Prefission constriction of Golgi tubular carriers driven by local lipid metabolism: a theoretical model.

Membrane transport within mammalian cells is mediated by small vesicular as well as large pleiomorphic transport carriers (TCs). A major step in the formation of TCs is the creation and subsequent narrowing of a membrane neck connecting the emerging carrier with the initial membrane. In the case of small vesicular TCs, neck formation may be directly induced by the coat proteins that cover the emerging vesicle. However, the mechanism underlying the creation and narrowing of a membrane neck in the generation of large TCs remains unknown. We present a theoretical model for neck formation based on the elastic model of membranes. Our calculations suggest a lipid-driven mechanism with a central role for diacylglycerol (DAG). The model is applied to a well-characterized in vitro system that reconstitutes TC formation from the Golgi complex, namely the pearling and fission of Golgi tubules induced by CtBP/BARS, a protein that catalyzes the conversion of lysophosphatidic acid into phosphatidic acid. In view of the importance of a PA-DAG cycle in the formation of Golgi TCs, we assume that the newly formed phosphatidic acid undergoes rapid dephosphorylation into DAG. DAG possesses a unique molecular shape characterized by an extremely large negative spontaneous curvature, and it redistributes rapidly between the membrane monolayers and along the membrane surface. Coupling between local membrane curvature and local lipid composition results, by mutual enhancement, in constrictions of the tubule into membrane necks, and a related inhomogeneous lateral partitioning of DAG. Our theoretical model predicts the exact dimensions of the constrictions observed in the pearling Golgi tubules. Moreover, the model is able to explain membrane neck formation by physiologically relevant mole fractions of DAG.

Biological Transport↗
PubMedDate not supplied

Modeling the temperature kinetics of aerobic solid-state biodegradation.

This study evaluated three models of microbial temperature kinetics using CO2 respiration data from aerobic solid-state biodegradation experiments. The models included those of Andrews and Kambhu/Haug, Ratkowsky et al., and the Cardinal Temperature Model with Inflection (CTMI) of Rosso et al. A parameter estimation routine implemented the Complex-Box search method for each model on 48 data sets collected during the composting of synthetic food waste or sewage-sludge (biosolids) mixed with maple wood chips at different oxygen concentrations and extents of decomposition. Each of the three nonlinear temperature kinetic functions proved capable of modeling a wide range of experimental data sets. However, the models differed widely in the consistency of their parameters. Parameters in the CTMI model were more stable over the course of the degradation process, and that variability which did arise was directly related to changes in the microbial process. Additional benefits of the CTMI model include the ease of parameter determinations, which can be approximated directly from laboratory experiments or full-scale system analysis, and the direct value of its parameters in engineering design and process control under a wide range of biodegradation conditions.

Bacteria, Aerobic↗
PubMed2005

The small G-protein Arf6GTP recruits the AP-2 adaptor complex to membranes.

The small GTP-binding protein ADP-ribosylation factor 6 (Arf6) is involved in plasma membrane/endosomes trafficking. However, precisely how the activation of Arf6 regulates vesicular transport is still unclear. Here, we show that, in vitro, recombinant Arf6GTP recruits purified clathrin-adaptor complex AP-2 (but not AP-1) onto phospholipid liposomes in the absence of phosphoinositides. We also show that phosphoinositides and Arf6 tightly cooperate to translocate AP-2 to the membrane. In vivo, Arf6GTP (but not Arf6GDP) was found associated to AP-2. The expression of the GTP-locked mutant of Arf6 leads to the plasma membrane redistribution of AP-2 in Arf6GTP-enriched areas. Finally, we demonstrated that the expression of the GTP-locked mutant of Arf6 inhibits transferrin receptor internalization without affecting its recycling. Altogether, our results demonstrated that Arf6GTP interacts specifically with AP-2 and promotes its membrane recruitment. These findings strongly suggest that Arf6 plays a major role in clathrin-mediated endocytosis by directly controlling the assembly of the AP-2/clathrin coat.

ADP-Ribosylation Factor 6↗
PubMed2005

Approaches for linking whole-body fish tissue residues of mercury or DDT to biological effects thresholds.

A variety of methods have been used by numerous investigators attempting to link tissue concentrations with observed adverse biological effects. This paper is the first to evaluate in a systematic way different approaches for deriving protective (i.e., unlikely to have adverse effects) tissue residue-effect concentrations in fish using the same datasets. Guidelines for screening papers and a set of decision rules were formulated to provide guidance on selecting studies and obtaining data in a consistent manner. Paired no-effect (NER) and low-effect (LER) whole-body residue concentrations in fish were identified for mercury and DDT from the published literature. Four analytical approaches of increasing complexity were evaluated for deriving protective tissue residues. The four methods were: Simple ranking, empirical percentile, tissue threshold-effect level (t-TEL), and cumulative distribution function (CDF). The CDF approach did not yield reasonable tissue residue thresholds based on comparisons to synoptic control concentrations. Of the four methods evaluated, the t-TEL approach best represented the underlying data. A whole-body mercury t-TEL of 0.2 mg/kg wet weight, based largely on sublethal endpoints (growth, reproduction, development, behavior), was calculated to be protective of juvenile and adult fish. For DDT, protective whole-body concentrations of 0.6 mg/kg wet weight in juvenile and adult fish, and 0.7 mg/kg wet weight for early life-stage fish were calculated. However, these DDT concentrations are considered provisional for reasons discussed in this paper (e.g., paucity of sublethal studies).

Animals↗
PubMed2005

Kaiso/p120-catenin and TCF/beta-catenin complexes coordinately regulate canonical Wnt gene targets.

Beta-catenin-dependent or canonical Wnt signals are fundamental in animal development and tumor progression. Using Xenopus laevis, we report that the BTB/POZ zinc finger family member Kaiso directly represses canonical Wnt gene targets (Siamois, c-Fos, Cyclin-D1, and c-Myc) in conjunction with TCF/LEF (TCF). Analogous to beta-catenin relief of TCF repressive activity, we show that p120-catenin relieves Kaiso-mediated repression of Siamois. Furthermore, Kaiso and TCF coassociate, and combined Kaiso and TCF derepression results in pronounced Siamois expression and increased beta-catenin coprecipitation with the Siamois promoter. The functional interdependency is underlined by Kaiso suppression of beta-catenin-induced axis duplication and by TCF-3 rescue of Kaiso depletion phenotypes. These studies point to convergence of parallel p120-catenin/Kaiso and beta-catenin/TCF signaling pathways to regulate gene expression in vertebrate development and possibly carcinogenesis.

Animals↗
PubMed2005

Effects of precursor and support variation in the genesis of uranium oxide catalysts for CO oxidation and selective reduction of NO: Synthesis and characterization.

A range of uranium oxide-based catalysts, derived from UO2(NO3)2.6H2O and UCl4 precursors, and supported on gamma-Al2O3, SiO2 and mesoporous H1SiO2, have been synthesized and then characterized using the following methods: isothermal nitrogen adsorption/desorption measurements, diffuse reflectance infrared spectroscopy (DRIFTS), gas titration of surface hydroxyl groups using Grignard reagents, U L(III) extended X-ray absorption fine structure (EXAFS), powder X-ray diffraction (PXRD), and thermogravimetric and differential thermal analysis. Brij76-templated H1SiO2 mesoporous silicas are found to be essentially stable under flowing oxygen after 16 h at 1073 K. At temperatures above this, however, extensive structural collapse, together with extensive dehydroxylation, ensues. Titration of the accessible hydroxyl group concentrations shows that in these materials the density of OH groups is considerably lower than in their amorphous counterparts. The adsorption of uranyl nitrate onto these dispersants results in a supported, and partially dehydrated, phase of the parent molecule with little obvious structural distortion; however, the adsorption of UCl4 leads to a complex adstructure which may best be described as U(O)2Cl2. The subsequent formation of the uranium oxide phase, nominally active for the oxidation of CO and selective reduction of NO (generally accepted to be U3O8), is found to be a considerable function of both the precursor and support system employed. Calcination of such systems to 1073 K results in extensive extrusion of the supported uranium phase from mesoporous supports, resulting in the formation of very large orthorhombic U3O8 domains. PXRD, however, shows that on amorphous SiO2 and gamma-Al2O3 similar treatment results in the formation of a hexagonal phase of U3O8. The formation of U3O8 is found to be promoted in mesoporous systems and by the presence of Cl in the catalyst make up. Some evidence is also found that suggests that a persistence of Cl limits the growth of U3O8 domains.

Journal Article↗
PubMed2006

Trichoderma brevicompactum complex: Rich source of novel and recurrent plant-protective polypeptide antibiotics (peptaibiotics).

Three strains of Trichoderma brevicompactum and another four that are closely related to that species (Trichoderma cf. brevicompactum) were analyzed for the formation of polypeptide antibiotics (peptaibiotics) by LC/ESI-MS(n). These isolates were selected because of an antagonistic potential against Eutypa dieback and Esca disease of grapevine and have not yet been investigated for the production of peptide antibiotics. Fully grown cultures on potato dextrose agar were extracted with CH2Cl2/MeOH, and this extract was subjected to SPE using C18 cartridges. The methanolic eluates were analyzed by LC/ESI-MS(n). All strains were found to produce membrane-active alamethicins F30. In addition to that, novel peptaibiotics were detected, namely, 14 12-residue trichocryptins B, 12 11-residue trichocryptins A, 19 11-residue trichobrevins A and B, 6 10-residue trichoferins, and 17 8-residue trichocompactins. These compounds may partially be responsible for the plant-protective action of the producers. Chemotaxonomic considerations also indicated the necessity to introduce another new species that is closely related to T. brevicompactum.

Anti-Bacterial Agents↗
PubMed2006

Neural induction promotes large-scale chromatin reorganisation of the Mash1 locus.

Determining how genes are epigenetically regulated to ensure their correct spatial and temporal expression during development is key to our understanding of cell lineage commitment. Here we examined epigenetic changes at an important proneural regulator gene Mash1 (Ascl1), as embryonic stem (ES) cells commit to the neural lineage. In ES cells where the Mash1 gene is transcriptionally repressed, the locus replicated late in S phase and was preferentially positioned at the nuclear periphery with other late-replicating genes (Neurod, Sprr2a). This peripheral location was coupled with low levels of histone H3K9 acetylation at the Mash1 promoter and enhanced H3K27 methylation but surprisingly location was not affected by removal of the Ezh2/Eed HMTase complex or several other chromatin-silencing candidates (G9a, SuV39h-1, Dnmt-1, Dnmt-3a and Dnmt-3b). Upon neural induction however, Mash1 transcription was upregulated (>100-fold), switched its time of replication from late to early in S phase and relocated towards the interior of the nucleus. This spatial repositioning was selective for neural commitment because Mash1 was peripheral in ES-derived mesoderm and other non-neural cell types. A bidirectional analysis of replication timing across a 2 Mb region flanking the Mash1 locus showed that chromatin changes were focused at Mash1. These results suggest that Mash1 is regulated by changes in chromatin structure and location and implicate the nuclear periphery as an important environment for maintaining the undifferentiated state of ES cells.

Animals↗
PubMed2003

X-ray structure of a protein-conducting channel.

A conserved heterotrimeric membrane protein complex, the Sec61 or SecY complex, forms a protein-conducting channel, allowing polypeptides to be transferred across or integrated into membranes. We report the crystal structure of the complex from Methanococcus jannaschii at a resolution of 3.2 A. The structure suggests that one copy of the heterotrimer serves as a functional translocation channel. The alpha-subunit has two linked halves, transmembrane segments 1-5 and 6-10, clamped together by the gamma-subunit. A cytoplasmic funnel leading into the channel is plugged by a short helix. Plug displacement can open the channel into an 'hourglass' with a ring of hydrophobic residues at its constriction. This ring may form a seal around the translocating polypeptide, hindering the permeation of other molecules. The structure also suggests mechanisms for signal-sequence recognition and for the lateral exit of transmembrane segments of nascent membrane proteins into lipid, and indicates binding sites for partners that provide the driving force for translocation.

Archaeal Proteins↗