Kinetic studies of amyloid beta-protein fibril assembly. Differential effects of alpha-helix stabilization

Amyloid beta-protein (Abeta) fibril assembly is a defining characteristic of Alzheimer's disease. Fibril formation is a complex nucleation-dependent polymerization process characterized in vitro by an initial lag phase. To a significant degree, this phase is a consequence of the energy barrier that must be overcome in order for Abeta monomers to fold and oligomerize into fibril nuclei. Here we show that low concentrations of 2,2,2-trifluoroethanol (TFE) convert predominately unstructured Abeta monomers into partially ordered, quasistable conformers. Surprisingly, this results in a temporal decrease in the lag phase for fibril formation and a significant increase in the rate of fibril elongation. The TFE effect is concentration dependent and is maximal at approximately 20% (v/v). In the presence of low concentrations of TFE, fibril formation is observed in Abeta samples at nanomolar concentration, well below the critical concentration for Abeta fibril formation in the absence of TFE. As the amount of TFE is increased above 20%, helix content progressively rises to approximately 80%, a change paralleled first by a decrease in elongation rate and then by a complete cessation of fibril growth. These findings are consistent with the hypothesis that a partially folded helix-containing conformer is an intermediate in Abeta fibril assembly. The requirement that Abeta partially folds in order to assemble into fibrils contrasts with the mechanism of amyloidogenesis of natively folded proteins such as transthyretin and lysozyme, in which partial unfolding is a prerequisite. Our results suggest that in vivo, factors that affect helix formation and stability will have significant effects on the kinetics of Abeta fibril formation.     

Contribution of microwave accelerated distillation in the extraction of the essential oil of Zygophyllum album L.

Introduction – The aerial parts of Zygophyllum album L. are used in folk medicine as an antidiabetic agent and as a drug active against several pathologies. In this work we present the chemical composition of Algerian essential oils obtained by microwave accelerated distillation (MAD) extraction, a solventless method assisted by microwave. Objective – Under the same analytical conditions and using GC‐FID and GC‐MS, the chemical composition of the essential oil of Zygophyllum album L. extracted by MAD was compared with that achieved using hydrodistillation (HD). Methodology – The extracted compounds were hydrosoluble, and they were removed from the aqueous solution by a liquid extraction with an organic solvent. Results – Employing MAD (100°C, 30 min), the essential oil contained mainly oxygenated monoterpenes with major constituents: carvone and α‐terpineol. However, most of the compounds present in the hydrodistilled volatile fraction were not terpene species, with β‐damascenone as a major constituent. Conclusion – The MAD method appears to be more efficient than HD: after 30 min extraction time, the obtained yields (i.e. 0.002%) were comparable to those provided by HD after 3 h extraction. MAD seems to be more convenient since the volatile fraction is richer in oxygenated monoterpenes, species that are recognised for their olfactory value and their contribution to the fragrance of the essential oil. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficacy of Beauveria bassiana (Bals.) Vuill. against the tarnished plant bug, Lygus lineolaris L., in strawberries

Beauveria bassiana has a high insecticidal potential to control the tarnished plant bug, Lygus lineolaris, a significant pest of strawberries. Screening experiments showed that L. lineolaris adults were susceptible to several B. bassiana isolates. Another screening test with Coleomegilla maculata, a natural enemy found in strawberries, was also performed in order to select the isolate having lower entomopathogenic impact on this insect. Based on data obtained from both insect species and on the ecozone origin of the B. bassiana isolates, INRS‐IP and INRS‐CFL isolates were selected for further experiments. The LC₅₀ values of these two isolates against L. lineolaris adults were 7.8 × 10⁵ and 5.3 × 10⁵ conidia/ml, and average survival time (AST) values were 4.46 and 4.37 days at a concentration of 1 × 10⁸ conidia/ml respectively. Results also indicated that L. lineolaris nymphs are susceptible to the selected isolates. During field experiments, using a randomized block design with four replicates, INRS‐IP and INRS‐CFL isolates were applied at two rates (1 × 10¹¹ and 1 × 10¹³ conidia/ha) weekly during a period of 4 weeks. These multiple applications triggered a significant reduction of L. lineolaris nymphal populations in strawberries. Twenty‐four days after the first application, a significant difference was observed between the mean population densities of surviving nymphs in all B. bassiana‐treated plots (less than one insect per five plants) compared with those in control plots (four insects per five plants). During the field experiment, persistence of insecticidal activity and viability of B. bassiana conidia were also monitored. The results showed the presence of viable and infective conidia up to 6 days after each application on strawberry foliage. Moreover, the multiple applications of B. bassiana at the rate of 1 × 10¹³ conidia/ha triggered a significant reduction in strawberry fruit injuries induced by L. lineolaris feeding behaviour compared with the control plots.     

Kinetic Behavior of Some Polyphosphate-Accumulating Bacteria Isolates in the Presence of Nitrate and Oxygen

This paper studies the phosphate uptake by pure cultures of Aeromonas hydrophila, Klebsiella oxytoca, Agrobacterium tumefaciens, and Aquaspirillum dispar in the presence of both nitrate and oxygen. It is shown that species were able to respire both electron acceptors for phosphate accumulation. A. tumefaciens and A. dispar accumulated overall phosphate both in oxic and anoxic culture conditions, whereas A. hydrophila and K. oxytoca eliminated overall phosphate only in oxic conditions. A. dispar was able to remove phosphate by reducing oxygen and nitrate simultaneously with the production of dinitrogen gas. The anoxic denitrification observed in the cultures of adapted and nonadapted cells to nitrate showed that only A. dispar have a denitrification rate superior when the cells were adapted to nitrate. Received: 15 December 1998 / Accepted: 21 January 1999     

Prey selection by nesting House Martins Delichon urbica Linné, 1758 (Aves: Hirundinidae) in Algiers suburbs (Algeria)

The diet of the House Martin Delichon urbica was analyzed in a suburban area in Pins maritimes, northeast of Algiers (Algeria). The diet was determined by analyzing 120 faecal samples collected from a breeding colony between April and September 2007. Insects were the most numerous prey types (99.86%). Hymenopterans were the dominant preys (56.99%), followed by Coleopterans (20.14%), Homopterans (14.22%), Heteropterans (5.45%), and Dipterans (3.10%). Division of the prey items into families demonstrated that the highest relative frequency was large Hymenopterans in the family Formicidae (54.0%). The dominant species in the diet was Tetramorium biskrensis, which comprised 32.6% of the diet. It was followed by Camponotus barbaricus (6.9%) and Monomorium salomonis (5.6%). Comparison between diet and availability of preys using the Savage index showed that T. biskrensis, Crematogaster scutelaris, Pheidole pallidula, Diptera sp. unident. and Aphidae sp. unident. were positively selected by D. urbica.     

Disruption of model-based decision making by silencing of serotonin neurons in the dorsal raphe nucleus

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SPAK/OSR1 regulate NKCC1 and WNK activity: analysis of WNK isoform interactions and activation by T-loop trans-autophosphorylation

Mutations in the WNK [with no lysine (K) kinase] family instigate hypertension and pain perception disorders. Of the four WNK isoforms, much of the focus has been on WNK1, which is activated in response to osmotic stress by phosphorylation of its T-loop residue (Ser382). WNK isoforms phosphorylate and activate the related SPAK (SPS1-related proline/alanine-rich kinase) and OSR1 (oxidative stress-responsive kinase 1) protein kinases. In the present study, we first describe the generation of double-knockin ES (embryonic stem) cells, where SPAK and OSR1 cannot be activated by WNK1. We establish that NKCC1 (Na+/K+/2Cl- co-transporter 1), a proposed target of the WNK pathway, is not phosphorylated or activated in a knockin that is deficient in SPAK/OSR1 activity. We also observe that activity of WNK1 and WNK3 are markedly elevated in the knockin cells, demonstrating that SPAK/OSR1 significantly influences WNK activity. Phosphorylation of another regulatory serine residue, Ser1261, in WNK1 is unaffected in knockin cells, indicating that this is not phosphorylated by SPAK/OSR1. We show that WNK isoforms interact via a C-terminal CCD (coiled-coil domain) and identify point mutations of conserved residues within this domain that ablate the ability of WNK isoforms to interact. Employing these mutants, we demonstrate that interaction of WNK isoforms is not essential for their T-loop phosphorylation and activation, at least for overexpressed WNK isoforms. Moreover, we finally establish that full-length WNK1, WNK2 and WNK3, but not WNK4, are capable of directly phosphorylating Ser382 of WNK1 in vitro. This supports the notion that T-loop phosphorylation of WNK isoforms is controlled by trans-autophosphorylation. These results provide novel insights into the WNK signal transduction pathway and provide genetic evidence confirming the essential role that SPAK/OSR1 play in controlling NKCC1 function. They also reveal a role in which the downstream SPAK/OSR1 enzymes markedly influence the activity of the upstream WNK activators. The knockin ES cells lacking SPAK/OSR1 activity will be useful in validating new targets of the WNK signalling pathway.     

Production of tannase by <Emphasis Type="Italic">Aspergillus niger</Emphasis> HA37 growing on tannic acid and Olive Mill Waste Waters

Production of tannase (tannin acyl hydrolase, EC 3.1.1.20) by Aspergillus nigerHA37 on a synthetic culture medium containing tannic acid at different concentrations has been studied. Maximal enzymatic activity increased according to the initial concentration of tannic acid; respectively 0.6, 0.9 and 1.5 enzyme activity units (EU) ml⁻¹ medium in the presence of 0.2%, 0.5% and 1% of tannic acid. Tannase production by A. niger HA37 on fourfold diluted olive mill waste waters (OMWW) as substrate, was between 0.37 and 0.65 EU ml⁻¹. Enzyme production on the diluted OMWW remained globally stable during more than 30 h. Growth of A. niger HA37 on OMWW was correlated with about 70% degradation of phenolic compounds present in the waste. This strain has therefore the capacity to degrade complex wastewaters which cause environmental damage to aquatic streams.