Membrane Trafficking of Death Receptors: Implications on Signalling

Death receptors were initially recognised as potent inducers of apoptotic cell death and soon ambitious attempts were made to exploit selective ignition of controlled cellular suicide as therapeutic strategy in malignant diseases. However, the complexity of death receptor signalling has increased substantially during recent years. Beyond activation of the apoptotic cascade, involvement in a variety of cellular processes including inflammation, proliferation and immune response was recognised. Mechanistically, these findings raised the question how multipurpose receptors can ensure selective activation of a particular pathway. A growing body of evidence points to an elegant spatiotemporal regulation of composition and assembly of the receptor-associated signalling complex. Upon ligand binding, receptor recruitment in specialized membrane compartments, formation of receptor-ligand clusters and internalisation processes constitute key regulatory elements. In this review, we will summarise the current concepts of death receptor trafficking and its implications on receptor-associated signalling events.     

The ATP/ADP Substrate Specificity Switch between Toxoplasma gondii NTPDase1 and NTPDase3 is Caused by an Altered Mode of Binding of the Substrate Base

Two nucleoside triphosphate diphosphohydrolase isoforms (NTPDase1 and NTPDase3) are responsible for the hydrolysis of nucleotides by the intracellular protozoan Toxoplasma gondii. They constitute about 3 % of the total parasite protein. Despite sharing 97 % sequence identity they exhibit opposite ATP versus ADP substrate discrimination ratios. Here we show by mutagenesis that the residues G492/G493 in NTPDase3 and R492/E493 in NTPDase1 are predominantly responsible for the differences in substrate specificity. Crystal structures of NTPDase1 in complexation with analogues of ATP and ADP reveal that the inverted substrate specificity of NTPDase1 relative to NTPDase3 is achieved by switching from the canonical substrate binding mode to a very different alternative one. Instead of being stacked on top of a helix of the C‐terminal domain the nucleotide base is positioned in the interdomain space between the side chains of R108 and R492, recruited from both domains. Furthermore, we show that the NTPDase1 substrate specificity is mainly dependent on the presence of the side chain of E493, which causes repositioning of the ribose component of the nucleotide. All in all, binding by the flexible side chains in the alternative binding mode in NTPDase1 allows for equally good positioning of ATP and ADP with increased activity toward ADP relative to what is seen in the case of NTPDase3.     

The Impact of Beneficial Plant-Associated Microbes on Plant Phenotypic Plasticity

Plants show phenotypic plasticity in response to changing or extreme abiotic environments; but over millions of years they also have co-evolved to respond to the presence of soil microbes. Studies on phenotypic plasticity in plants have focused mainly on the effects of the changing environments on plants’ growth and survival. Evidence is now accumulating that the presence of microbes can alter plant phenotypic plasticity in a broad range of traits in response to a changing environment. In this review, we discuss the effects of microbes on plant phenotypic plasticity in response to changing environmental conditions, and how this may affect plant fitness. By using a range of specific plant-microbe interactions as examples, we demonstrate that one way that microbes can alleviate the effect of environmental stress on plants and thus increase plant fitness is to remove the stress, e.g., nutrient limitation, directly. Furthermore, microbes indirectly affect plant phenotypic plasticity and fitness through modulation of plant development and defense responses. In doing so, microbes affect fitness by both increasing or decreasing the degree of phenotypic plasticity, depending on the phenotype and the environmental stress studied, with no clear difference between the effect of prokaryotic and eukaryotic microbes in general. Additionally, plants have the ability to modulate microbial behaviors, suggesting that they manipulate bacteria, enhancing interactions that help them cope with stressful environments. Future challenges remain in the identification of the many microbial signals that modulate phenotypic plasticity, the characterization of plant genes, e.g. receptors, that mediate the microbial effects on plasticity, and the elucidation of the molecular mechanisms that link phenotypic plasticity with fitness. The characterization of plant and microbial mutants defective in signal synthesis or perception, together with carefully designed glasshouse or field experiments that test various environmental stresses will be necessary to understand the link between molecular mechanisms controlling plastic phenotypes with the resulting effects on plant fitness.     

Ungewöhnliche Adsorptions‐ und Trenneigenschaften des Molekularsiebs ZIF‐8

Low‐temperature rectification represents the state‐of the‐art in olefin/paraffin separation. Adsorption on microporous coordination polymers could be a less energy and cost‐intensive alternative. Especially zeolitic imidazolate frameworks, such as ZIF‐8, exhibits an interesting adsorption behavior since alkanes are preferentially adsorbed in comparison with the corresponding olefins. The single‐component adsorption isotherms and mixed gas breakthrough experiments of C₂ to C₄ hydrocarbons show the potential of ZIF‐8 for olefin/paraffin separation.     

Spheres on spheres – a novel spherical multiphase morphology in polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymers

A novel morphology for linear ABC-triblock copolymers is presented, where A forms spherical microdomains, covered by small B-spheres and C forming the matrix. This morphology is characterized by transmission electron microscopy and small angle X-ray scattering. The morphology forms both in solution cast and melt extruded samples. Qualitative arguments to understand the thermodynamic stability of this morphology are given. Received: 2 December 1997/Accepted: 3 December 1997     

Modeling and Parameter Identification for a Biofilm in a Microbial Fuel Cell

A dynamic physical model of a microbial fuel cell (MFC) anode is presented and parameterized. It describes the evolution of current density and biofilm mass over time as a function of substrate concentration. The model is particularly useful for process monitoring or control purposes because it reproduces the dynamics of the MFC anode and contains comparatively few parameters. Parameters are identified using data from the response of the MFC to a substrate concentration pulse. Theoretical and practical identifiability of the parameters is evaluated, and parameter confidence intervals are determined.     

The Conversion of UDP-Glc to UDP-Man: In Silico and Biochemical Exploration To Improve the Catalytic Efficiency of CDP-Tyvelose C2-Epimerases

A promiscuous CDP-tyvelose 2-epimerase (TyvE) from Thermodesulfatator atlanticus (TaTyvE) belonging to the nucleotide sugar active short-chain dehydrogenase/reductase superfamily (NS-SDRs) was recently discovered. TaTyvE performs the slow conversion of NDP-glucose (NDP-Glc) to NDP-mannose (NDP-Man). Here, we present the sequence fingerprints that are indicative of the conversion of UDP-Glc to UDP-Man in TyvE-like enzymes based on the heptagonal box motifs. Our data-mining approach led to the identification of 11 additional TyvE-like enzymes for the conversion of UDP-Glc to UDP-Man. We characterized the top two wild-type candidates, which show a 15- and 20-fold improved catalytic efficiency, respectively, on UDP-Glc compared to TaTyvE. In addition, we present a quadruple variant of one of the identified enzymes with a 70-fold improved catalytic efficiency on UDP-Glc compared to TaTyvE. These findings could help the design of new nucleotide production pathways starting from a cheap sugar substrate like glucose or sucrose.     

Eigenschaften von Gießfilmen aus nativen und chemisch modifizierten Stärken

Properties of Casting Films from Native and Chemically Modified Starches. Starch acetates and hexanoates were prepared from potato, wrinkled pea, and amylomaize starch of low and high degrees of substitution (DS=0.1-2.8). These products were used as raw materials for film casting in a laboratory scale. The objective of this work was to study the influence of starch types and derivatisations on film properties, i.e. tensile strength and elongation as well as water absorption and solubility. After the addition of softeners transparent, flexible, and water soluble films were obtained from unsubstituted and partially substituted starches, while totally substituted starch derivatives (triacetates and hexanoates) resulted in films insoluble in water. The well-known amylose advantage of film casting was found only after derivatisation. In the case of wrinkled pea and amylomaize starch considerable improvements of mechanical film properties, both tensile strength and elongation, were achieved even at low degrees of substitution.     

Sea transport of bananas in containers – Parameter identification for a temperature model

Losses of product quality during the sea transport of bananas in containers are related to the emergence of hot spots. In order to analyze critical conditions, a spatial temperature profile was recorded ashore in a container loaded with banana pallets. The identification of a structured system model showed that it is possible to reduce the information on the measured temperature curves to a set of only two index values. These can be interpreted as factors for coupling to the air stream and for the amount of heat generated by biological processes per banana box. The width of gaps between pallets was identified as the major influence on the spatial temperature profile. Boxes from which the unwanted banana ripening heat cannot be channeled away by the cooling unit can be detected by the quotient of the index values.