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See detailInfluence of protein context on the propensity of polyglutamine tracts to trigger protein aggregation into amyloid fibrils
Huynen, Céline ULg

Poster (2012, September 10)

Nine neurodegenerative diseases, referred to as polyglutamine diseases, are associated with nine proteins containing an expanded polyglutamine (polyQ) tract. PolyQ tracts are encoded by a repetition of ... [more ▼]

Nine neurodegenerative diseases, referred to as polyglutamine diseases, are associated with nine proteins containing an expanded polyglutamine (polyQ) tract. PolyQ tracts are encoded by a repetition of the CAG codon in the corresponding genes, and are present in proteins of healthy people. They are however pathogenic when their length, due to mutations, becomes higher than a threshold generally comprised between 35 and 45Q. Such pathological tracts trigger the aggregation of the proteins into amyloid-like aggregates that could play an important role in the disease. It is therefore necessary to investigate at a molecular level the aggregation process of polyQ proteins. Since proteins associated with polyQ diseases are generally large and relatively insoluble, they are difficult to produce and handle experimentally. We have therefore decided to study the aggregation properties of polyQ proteins by designing and characterizing model proteins made of a well-characterized host protein, the β-lactamase BlaP, and polyQ tracts of different lengths (23 to 79Q) inserted either at positions 197 or 216 of BlaP. The aggregation behaviour of BlaP chimeras recapitulate those of proteins associated with polyQ diseases. We indeed observed that there is a minimal number of glutamines (i.e. a threshold) required for the chimeras’ aggregation into amyloid-like fibrils and that the kinetics of aggregation are faster with longer glutamine repeats. Most importantly, the value of the threshold for amyloid-like fibril formation seems to critically depend on the structural integrity of BlaP and thus on the constraints applied to the polyQ tract. In the present work, we investigate more deeply the role of the protein context and of oligomers on the aggregation process of BlaP chimeras. This study is mainly based on the use of two techniques: the quartz crystal microbalance with dissipation (QCM-D) in combination with atomic force microscopy (AFM), and the dynamic light scattering (DLS). QCM-D studies indicate that, under native condition, there is a minimal number of glutamines required for the elongation of BlaP197(Gln)79 fibrils by BlaP chimeras containing a polyQ tract in position 197. This threshold is lower than that observed for the aggregation assays monitored in solution in the absence of seed; it corresponds however to the threshold for fibril formation observed under denaturing conditions. These observations suggest that the conformation of BlaP is the limiting step for amyloid fibril formation by interfering with the nucleation step. BlaP chimeras containing 55Q or more in position 216 of BlaP also elongate BlaP197(Gln)79 fibrils. Interestingly this rate of cross-elongation is faster than the elongation rate observed with BlaP197(Gln)55 and BlaP197(Gln)79. This observation demonstrates that the protein environment of the polyQ tract influences its propensity to form amyloid fibrils. Finally, preliminary DLS experiments indicate that oligomers formed by BlaP197(Gln)79 under native condition are on-pathway of amyloid fibril formation and could act as aggregation nuclei. [less ▲]

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See detailInfluence of purified dietary fibre on bacterial protein synthesis in the large intestine of pigs, as measured by the gas production technique.
Bindelle, Jérôme ULg; Buldgen, André; Michaux, David et al

in Livestock Science (2007), 109

Microbial fermentation of non-digestible carbohydrates in the pig's large intestine induces a shift of N excretion from urea in urine to bacterial protein in faeces. Experiments were carried out to ... [more ▼]

Microbial fermentation of non-digestible carbohydrates in the pig's large intestine induces a shift of N excretion from urea in urine to bacterial protein in faeces. Experiments were carried out to measure the mineral N incorporation by the pig intestinal microflora using 5 purified carbohydrates in a gas-test: starch (S), cellulose (C), inulin (I), pectin (P) and xylan (X). Fermentation kinetics was modelled. N source in the buffer solution was replaced by 15N labelled NH4Cl. The bacterial N fixation was determined at mid-fermentation, measuring 15N incorporation into the solid phase of the buffer. The bacterial N fixation was higher (Pb0.001) with I and S (19.9 and 18.1 mg N/g incubated DM), compared to P, C and X (8.7, 5.9 and 5.5 respectively). Inulin and S were fermented also more rapidly, even if I (0.081 h−1) and C (0.074 h−1) showed lower half time fractional rate of degradation than S (0.153 h−1), P (0.133 h−1) and X (0.104 h−1). The insoluble dietary fibre content of the substrates was negatively correlated to bacterial N fixation (r=−0.957, P=0.011). The high crude protein content of P (32.5 mg g−1DM) might explain the lower impact of this substrate on bacterial N fixation, despite its rapid fermentation. Beside the proportion of insoluble fibre, the N content and the rate of fermentation seem to be the major factors influencing bacterial protein synthesis. Further studies including ingredients with variable content of indigestible protein and mean retention time in the pig's intestines are necessary. [less ▲]

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See detailInfluence of residual alpha-amylase activity on the pasting properties of extracted wheat starch.
Lenartz, Jonathan; Sinnaeve, Georges; Massaux, Carine et al

Poster (2005, June)

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See detailInfluence of response factors on determining equilibrium association constants of non-covalent complexes by electrospray ionization mass spectrometry
Gabelica, Valérie ULg; Galic, Nives; Rosu, Frédéric ULg et al

in Journal of Mass Spectrometry [=JMS] (2003), 38(5), 491-501

A method for determining the equilibrium association constant of a complexation reaction A + B <=> AB by electrospray ionization mass spectrometry is described. The method consists in measuring the ... [more ▼]

A method for determining the equilibrium association constant of a complexation reaction A + B <=> AB by electrospray ionization mass spectrometry is described. The method consists in measuring the relative intensities of the peaks corresponding to A and to AB in equimolar A–B solutions at different concentrations C0. The results are fitted by a non-linear least-squares procedure, with the two variable parameters being the equilibrium association constant Ka and a factor R, defined by I(AB)/I.A/ = R× [AB]/[A]. The factor R is the ratio between the response factors of AB and A, and corrects for the relative electrospray responses of the complex and the free substrate A, mass discrimination of instrumental origin and/or moderate in-source dissociation. The method is illustrated with the following two systems: complexes between a double-stranded 12-base pair oligonucleotide and minor groove binders, and cyclodextrin complexeswith a,!-dicarboxylic acids. For the oligonucleotide complexes, it is found that the response of the complex is not dramatically different to the response of the free oligonucleotide duplex, as the double helix conformation is disturbed by the drug only to a minor extent. In the case of cyclodextrin complexes, these complexes were found to have a much higher response than free cyclodextrin. This may be due to the fact that cyclodextrin is neutral in solution, whereas the complex is charged, but it can also stem from the fact that a significant proportion of the complex is in a non-inclusion geometry. The present method requires the exact determination of the concentrations of the reactants and is applicable to 1 : 1 complexes. [less ▲]

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See detailInfluence of response prepotency strength, general working memory resources, and specific working memory load on the ability to inhibit predominant responses: A comparison of young and elderly participants
Grandjean, Julien ULg; Collette, Fabienne ULg

in Brain & Cognition (2011), 77

One conception of inhibitory functioning suggests that the ability to successfully inhibit a predominant response depends mainly on the strength of that response, the general functioning of working memory ... [more ▼]

One conception of inhibitory functioning suggests that the ability to successfully inhibit a predominant response depends mainly on the strength of that response, the general functioning of working memory processes, and the working memory demand of the task (Roberts, Hager, and Heron, 1994). The proposal that inhibition and functional working memory capacity interact was assessed in the present study using two motor inhibition tasks (Go/No-Go and response incompatibility) in young and older participants. The strength of prepotency was assessed with a short or long training phase for the response to be inhibited. The influence of working memory resources was evaluated by administering the tasks in full versus divided attention conditions. The effect of working memory load was manipulated by increasing the number of target and distracter items in each task. Results showed no effect of prepotency strength, whereas dividing attentional resources and increasing working memory load were associated with greater inhibitory effects in both groups and for both tasks. This deleterious effect was higher for older participants, except in the working memory load condition of the Go/No-Go task. These results suggest an interactive link between working memory and response inhibition by showing that taxing working memory resources increases the difficulty of inhibiting prepotent responses in younger and older subjects. The additional detrimental effect of these factors on healthy elderly subjects was related to their decreased cognitive resources and to their shorter span size. [less ▲]

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See detailInfluence of rhizobacterial volatile compounds on growth and root system architecture of Brachypodium distachyon (L.) Beauv.
Mendaluk, Magdalena ULg; Varin, Sébastien; Baudson, Caroline ULg et al

Poster (2013, February 08)

Many rhizobacterial strains are classified as plant growth-promoting rhizobacteria (PGPR) and are potentially useful to enhance plant fitness and productivity. Among the mechanisms by which PGPR improve ... [more ▼]

Many rhizobacterial strains are classified as plant growth-promoting rhizobacteria (PGPR) and are potentially useful to enhance plant fitness and productivity. Among the mechanisms by which PGPR improve plant growth, the emission of volatile organic compounds (VOCs) and their biological impacts on plants remain little documented. The aim of this work is to evaluate the growth promotion ability of 19 bacterial strains on the model grass Brachypodium distachyon Bd21 (Bd21), with a focus on this peculiar mode of interaction. A collection of 19 strains was selected for their known growth promotion potential. The impact of the rhizobacteria on the model grass was studied using an in vitro cocultivation system allowing interactions through VOCs without physical contact between plants and bacteria. The results show that the VOCs of several strains promote total biomass production, modulate biomass partitioning and affect shoot and root architecture of Bd21. The effects of the PGPR strains emitting different volatile blends were investigated via principal component analysis coupled to clustering and univariate analysis to unravel their biological effects. On the basis of volatile emissions and of their effects on plant growth, two strains have been selected in order to evaluate such interactions using an ex vitro system. The set-up of this system is in progress. [less ▲]

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See detailInfluence of rhizosphere-specific parameters on surfactin production by Bacillus subtilis.
Ongena, MARC ULg; Nihorimbere, Venant; Fickers, Patrick ULg et al

in Bulletin OILB/SROP = IOBC/WPRS Bulletin (2009), (43), 317-320

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See detailInfluence of rhizosphere-specific parameters on surfactin production by Bacillus subtilis.
Nihorimbere, V.; Fickers, P.; Thonart, Philippe ULg et al

Conference (2008, September)

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See detailInfluence of salt restriction in untreated essential hypertension patients
Krzesinski, Jean-Marie ULg; Du, F.; Pequeux, L. et al

in Journal of Hypertension (1992), 10(10), 1297-1298

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See detailInfluence of sampling effort on saproxylic beetle diversity assessment: Implications for insect monitoring studies in European temperate forests
Parmain, G.; Dufrêne, Marc ULg; Brin, A. et al

in Agricultural & Forest Entomology (2013)

Saproxylic beetle diversity monitoring provides a tool for estimating the efficiency of forest conservation measures. Flight interception traps are commonly employed to monitor beetle assemblages ... [more ▼]

Saproxylic beetle diversity monitoring provides a tool for estimating the efficiency of forest conservation measures. Flight interception traps are commonly employed to monitor beetle assemblages, although little explicit knowledge of the efficiency of this trapping method is available. The present study investigated how slight changes in sampling effort can influence species richness and species composition of assemblages in data sets from standard window-flight traps. At both trap and plot levels, an additional year or an additional trap provided a 50% increase in the number of species detected (a 75% increase for rare species) and resulted in a different estimated composition of the assemblages. Adding 2 or 3years of sampling gave twice as many species and resulted in assemblages that were 50% dissimilar. Increases in the detection of species and the dissimilarity of assemblages were similarly affected along a gradient of forest conditions, suggesting that changes in sampling effort were not affected by forest condition. At the forest level, year or trap replication provided smaller increases in species richness (31% and 25%, respectively). Within sites, distance measures in species composition between traps did not differ significantly when based on 1 or 2years of data. Using two traps per plot compared with one trap influenced comparisons between stand types, based on species richness, in 25% of the cases. Species detection was similarly increased by either year replication or trap replication. The results of the present study highlight the significant role played by finescale patterns of habitat structure and inter-annual variation with respect to determining catch size and assemblages of saproxylic species. © 2013 The Royal Entomological Society. [less ▲]

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See detailInfluence of sedatives, anticonvulsants and a negative chronotrope on transcranial doppler ultrasonography
de Laat, B. W. G. A.; Gommeren, Kris ULg; Denies, S. et al

in Proceedings of the 22nd ECVIM-CA Congress (2012, September)

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See detailThe influence of sediment size, relative grain size and channel slope on initiation of sediment motion in boulder bed rivers. A lichenometric study
Gob, F.; Bravard, J. P.; Petit, François ULg

in Earth Surface Processes & Landforms (2010), 35

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See detailInfluence of sedimentary setting on the use of magnetic susceptibility : examples from the Devonian of Belgium
Da Silva, Anne-Christine ULg; Mabille, Cédric ULg; Boulvain, Frédéric ULg

in Sedimentology (2009), 56

Bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea-level variations ... [more ▼]

Bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea-level variations. This paper explores the link between magnetic susceptibility, depositional setting and environmental parameters. These environmental parameters include distal–proximal transects, microfacies successions and fourth-order trends on different carbonate platform types (platform, ramp, carbonate mound or atoll) during different Devonian stages (Eifelian, Givetian and Frasnian). Average magnetic susceptibility values over a distal–proximal-trending facies succession vary markedly with depositional setting. On carbonate platforms, average magnetic susceptibility generally increases towards the top of shallowing-upward sequences. On a distal–proximal transect, average magnetic susceptibility is intermediate for the deepest facies, decreases for the reef belts and increases to a maximum in the back-reef zone. In ramps and atolls, magnetic susceptibility trends clearly differ; average magnetic susceptibility generally decreases towards the top of shallowing-upward sequences and is highest in the deepest facies. The strong relationship between magnetic susceptibility, facies and sequences implies a strong environmental influence. However, the different responses in the different latform types suggest that sea-level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values. Other primary or secondary processes also probably influenced magnetic mineral distribution. Primary processes such as carbonate production and water agitation during deposition are probably key factors. When carbonate production is high, the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases. High water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values. These parameters explain the lowest values observed on the reef platform, inner ramp and atoll crown, which are all in areas characterized by higher carbonate production and greater water agitation during deposition. The lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown. However, other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal. Diagenesis can change magnetism by creating or destroying magnetic minerals. However, the influence of diagenesis probably is linked strongly to the primary facies (permeability, amount of clay or organic matter) and probably enhanced the primary signal. The complexity of the signal gives rise to correlation problems between different depositional settings. Thus, while magnetic susceptibility has the potential to be an important correlation tool, the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and depositional environments and without strongbiostratigraphical control. [less ▲]

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See detailInfluence of selected parameters on the flotation of Cu-Mo ore from Ellatzite deposit in Bulgaria
Gaydardzhiev, Stoyan ULg; Bouchat, Harold ULg; Dedelyanova, K et al

in Proceedings of the XXVI International Mineral Processing Congress (2012, September)

Laboratory batch tests having preliminary and orientation character aiming at improvement of the molybdenum flotation at Ellatzite copper processing plant in Bulgaria have been conducted. The following ... [more ▼]

Laboratory batch tests having preliminary and orientation character aiming at improvement of the molybdenum flotation at Ellatzite copper processing plant in Bulgaria have been conducted. The following technological parameters have been screened to study their influence on the grade and recovery of copper and molybdenum during the rougher flotation stage: flotation pulp density, pH, addition of secondary collector and replacement of MIBC by pine oil as a frother. The results have shown that slightly better grade/recovery figures could be obtained for both copper and molybdenum at lower flotation pulp densities. The addition of kerosene has improved the recovery of molybdenum however on the expense of that of copper. The effects from pH variation and the replacement of MIBC by pine oil as a frother have been almost negligible. [less ▲]

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