An Unusual Fatty Acyl:Adenylate Ligase (FAAL)–Acyl Carrier Protein (ACP) Didomain in Ambruticin Biosynthesis

The divinylcyclopropane (DVC) fragment of the ambruticins is proposed to be formed by a unique polyene cyclisation mechanism, in which the unusual didomain AmbG plays a key role. It is proposed to activate the branched thioester carboxylic acid resulting from polyene cyclisation and to transfer it to its associated acyl carrier protein (ACP). After oxidative decarboxylation, the intermediate is channelled back into polyketide synthase (PKS) processing. AmbG was previously annotated as an adenylation–thiolation didomain with a very unusual substrate selectivity code but has not yet been biochemically studied. On the basis of sequence and homology model analysis, we reannotate AmbG as a fatty acyl:adenylate ligase (FAAL)–acyl carrier protein didomain with unusual substrate specificity. The expected adenylate‐forming activity on fatty acids was confirmed by in vitro studies. AmbG also adenylates a number of structurally diverse carboxylic acids, including functionalised fatty acids and unsaturated and aromatic carboxylic acids. HPLC‐MS analysis and competition experiments show that AmbG preferentially acylates its ACP with long‐chain hydrophobic acids and tolerates a π system and a branch near the carboxylic acid. AmbG is the first characterised example of a FAAL–ACP didomain that is centrally located in a PKS and apparently activates a polyketidic intermediate. This is an important step towards deeper biosynthetic studies such as partial reconstitution of the ambruticin pathway to elucidate DVC formation.     

Nanoscopic Characterisation of Individual Endogenous Protein Aggregates in Human Neuronal Cells

The aberrant misfolding and subsequent conversion of monomeric protein into amyloid aggregates characterises many neurodegenerative disorders, including Parkinson's and Alzheimer's diseases. These aggregates are highly heterogeneous in structure, generally of low abundance and typically smaller than the diffraction limit of light (≈250 nm). To overcome the challenges these characteristics pose to the study of endogenous aggregates formed in cells, we have developed a method to characterise them at the nanometre scale without the need for a conjugated fluorophore. Using a combination of DNA PAINT and an amyloid‐specific aptamer, we demonstrate that this technique is able to detect and super‐resolve a range of aggregated species, including those formed by α‐synuclein and amyloid‐β. Additionally, this method enables endogenous protein aggregates within cells to be characterised. We found that neuronal cells derived from patients with Parkinson's disease contain a larger number of protein aggregates than those from healthy controls.     

Temperature-, pH-, and magnetic-field-sensitive hybrid microgels

We demonstrate a simple route for the preparation of novel hybrid particles with multiple sensitivities. Aqueous polymeric microgels are modified by magnetite nanoparticles in the preparation of temperature- and pH-sensitive hybrids with a high magnetic response. Up to 15 wt % of magnetite nanoparticles are loaded into microgels. The influence of the amount of magnetite in the microgel structure on the morphology and colloidal properties is discussed. The presence of the magnetite nanoparticles in the microgel decreases its degree of swelling and shifts the volume phase-transition temperature to higher values. Nanostructured composite films with controlled morphologies can be prepared by water evaporation and deposition of the hybrid microgels on a solid substrate.     

Deciphering the sulfate attack of cementitious materials by high-resolution micro-X-ray diffraction

The durability of cementitious materials depends, among others, on their resistance against chemical attack during the service life of a building. Here, we present an approach to analyze changes in the phase composition due to chemical attack in the form of sulfate ingress within the microstructure. Micro-X-ray (μX-ray) diffraction using synchrotron radiation in Debye-Scherrer (transmission) geometry allowed a spatial resolution of 10 μm. Phase transformations in the wake of damaging processes were observed in a detailed high-resolution imaging study. In comparison, samples containing supplementary cementitious materials were investigated and used to reconstruct the influence of different degeneration processes in detail. Additionally, reaction fronts within the bulk were localized by micro-X-ray fluorescence analysis. The experimental setup provided the possibility for analyzing the phase assemblage of a given sample without destroying the microstructure. The specimens for phase analysis are thick sections of the primary material and can be used for further microscopic analysis of the microstructure and microchemistry, e.g., scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) or Raman spectroscopy.     

Carbon nanotube nanoelectronic devices compatible with transmission electron microscopy

We report on a novel method to fabricate carbon nanotube (CNT) nanoelectronic devices on silicon nitride membrane grids that are compatible with high resolution transmission electron microscopy (HRTEM). Resist-based electron beam lithography is used to fabricate electrodes on 50 nm thin silicon nitride membranes and focused-ion-beam milling is used to cut out a 200 nm gap across a gold electrode to produce the viewing window for HRTEM. Spin-coating and AC electrophoresis are used as methods to deposit small bundles of carbon nanotubes across the electrodes. We demonstrate the viability of this approach by performing both electrical measurements and HRTEM imaging of solution-processed CNTs in a device.     

Utilizing boron nitride sheets as thin supports for high resolution imaging of nanocrystals

We demonstrate the use of thin BN sheets as supports for imaging nanocrystals using low voltage (80 kV) aberration-corrected high resolution transmission electron microscopy. This provides an alternative to the previously utilized 2D crystal supports of graphene and graphene oxide. A simple chemical exfoliation method is applied to get few layer boron nitride (BN) sheets with micrometer-sized dimensions. This generic approach of using BN sheets as supports is shown by depositing Mn doped ZnSe nanocrystals directly onto the BN sheets and resolving the atomic structure from both the ZnSe nanocrystals and the BN support. Phase contrast images reveal moiré patterns of interference between the beams diffracted by the nanocrystals and the BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes. Double diffraction is observed and has been analyzed.     

Information Costs in International Business: Analyzing the Effects of Economies of Scale,Cultural Diversity and Decentralization

The relationship between internationalization and performance is controversial. Prominent in the theoretical arguments about a performance downturn in internationalization are increasing information, coordination, and management costs—an argument for which empirical insights are lacking. Building on a model of information cost, we test for the development of internal information costs during internationalization. Applying a panel procedure on a data set of top manufacturers observed over a 7-year period, we analyze the effects of economies of scale, multinationality or host market diversity and international organizational decentralization on internal information costs. Although internal information costs decline due to economies of scale in international business, they are especially affected by the degree of host market diversity: a growing cultural diversity increases internal information costs per unit. Finally, we find that after a phase of first organizational adaptation processes, international organizational decentralization (and therewith complexity) rises internal information costs. Information cost development plays a major role in theories referring to a performance downswing in a phase of high or culturally unrelated internationalization involving strong organizational complexity. Our results offer empirical backing for these arguments on internal information costs (incorporated into an information cost model).     

A 2D closed form model for the electrostatics in hetero-junction double-gate tunnel-FETs for calculation of band-to-band tunneling current

In the last few years the Tunnel-FET has become one of the promising devices to be the successor of the MOSFET due to its CMOS compatibility and steep subthreshold slopes (S) below 60 mV/dec. Hetero-junctions at the channel interface are used to improve the on-state current of the device. In this paper a 2D physics-based analytical model for hetero-junction Tunnel-FETs is introduced. It predicts a 2D band-to-band tunneling probability calculation through Wentzel–Kramers–Brillouin approximation (WKB) based on a 2D solution of electrostatics with respect to the device structure and carrier distributions in the device. These results are embedded in a model for the device current. The solutions of the potential, electrical field and the current transfer characteristics of the model are in good agreement with simulation data from the finite-element-method (FEM) simulator TCAD Sentaurus.     

The effect of positive events at work on after-work fatigue: They matter most in face of adversity.

There is evidence that daily negative events at work enhance fatigue. In contrast, positive events may trigger processes that increase, but also processes that decrease, energetic resources. Accordingly, results regarding a main effect of positive events on fatigue have been mixed. However, a clearer pattern between positive events and fatigue can be expected under adverse circumstances (i.e., accumulation of negative events, high chronic stressors). Positive events may facilitate coping and accelerate recovery processes and, thus, reduce resource drain due to daily negative events and chronic stressors. Predicting fatigue in a diary study with 76 employees, we investigated interactions between daily positive events and (a) daily negative events and (b) chronic social stressors. Multilevel modeling revealed that negative but not positive events were associated with increased end-of-work fatigue. However, positive events interacted with negative events and with chronic social stressors. As expected, positive events were negatively associated with fatigue only on days with many negative events, but not so on days with few negative events. Analogously, positive events were negatively associated with fatigue only among employees with high, compared with low, chronic social stressors. We conclude that the beneficial short-term effects of positive events on energetic resources are largely confined to adverse circumstances. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Hypusinated eIF5A Promotes Ribosomal Frameshifting during Decoding of ODC Antizyme mRNA in Saccharomyces cerevisiae

Polyamines are essential biogenic poly-cations with important roles in many cellular processes and diseases such as cancer. A rate-limiting step early in the biosynthesis of polyamines is the conversion of ornithine to putrescine by the homodimeric enzyme ornithine decarboxylase (ODC). In a conserved mechanism of posttranslational regulation, ODC antizyme (OAZ) binds to ODC monomers promoting their ubiquitin-independent degradation by the proteasome. Decoding of OAZ mRNA is unusual in that it involves polyamine-regulated bypassing of an internal translation termination (STOP) codon by a ribosomal frameshift (RFS) event. Using Saccharomyces cerevisiae, we earlier showed that high polyamine concentrations lead to increased efficiency of OAZ1 mRNA translation by binding to nascent Oaz1 polypeptide. The binding of polyamines prevents stalling of the ribosomes on OAZ1 mRNA caused by nascent Oaz1 polypeptide thereby promoting synthesis of full-length Oaz1. Polyamine depletion, however, also inhibits RFS during the decoding of constructs bearing the OAZ1 shift site lacking sequences encoding the Oaz1 parts implicated in polyamine binding. Polyamine depletion is known to impair hypusine modification of translation factor eIF5A. Using a novel set of conditional mutants impaired in the function of eIF5A/Hyp2 or its hypusination, we show here that hypusinated eIF5A is required for efficient translation across the OAZ1 RFS site. These findings identify eIF5A as a part of Oaz1 regulation, and thereby of polyamine synthesis. Additional experiments with DFMO, however, show that depletion of polyamines inhibits translation across the OAZ1 RFS site not only by reducing Hyp2 hypusination, but in addition, and even earlier, by affecting RFS more directly.