Synthèse de dérivés glucosylés du 1,5-anhydro-D-fructose à l'aide de glucane-saccharases natives et recombinantes

Le développement d’un procédé de synthèse de l’AF catalysée par l’-(1,4) glucane-lyase rend\ud aujourd’hui la molécule facilement accessible à partir d’amidon. Sa valorisation fait l’objet du projet\ud européen NEPSA auquel sont intégrés mes travaux de thèse. Ils sont focalisés sur la synthèse de\ud dérivés glucosylés de l’AF à l’aide de glucane-saccharases (GS). Ces enzymes catalysent à partir de\ud saccharose le transfert d’unités glucosyle sur des molécules exogènes dites acceptrices.\ud Pour la première fois, il a été démontré que l’AF est reconnu comme accepteur par les GS\ud produites par des souches de Leuconostoc mesenteroides et Neisseria polysaccharea. Les produits de\ud glucosylation sont des anhydro-D-fructo-glucooligosaccharides (AFGOS) résultant de transferts\ud successifs d’unités glucosyle sur l’AF. Des familles d’AFGOS de structures différentes peuvent être\ud synthétisées par l’utilisation de GS de spécificités distinctes.\ud Les AFGOS produits par la réaction d’accepteur conservent un fort pouvoir anti-oxydant mais sont\ud dépourvus de propriétés prébiotiques. La réactivité particulière de l’AF a également été mise à profit\ud pour la dérivation quantitative, spécifique et rapide de l’AF et des AFGOS en oximes.\ud La production des AFGOS a été optimisée en contrôlant le rapport molaire saccharose/AF et la\ud matière sèche pour atteindre des taux de conversion compris entre 50 et 80 % selon la GS utilisée.\ud D’autre part, l’utilisation de variants de GS obtenus par ingénierie rationnelle permet d’améliorer\ud encore la glucosylation de l’AF. Pour isoler de nouvelles enzymes plus efficaces par criblage de\ud banques de variants générés par ingénierie combinatoire, une méthode basée sur la réduction\ud spécifique de l’AF a été développée.\ud The development of the of 1,5-anhydro-D-fructose (AF) production from starch catalysed by -(1,4)\ud glucanlyase makes now AF easily available. Its valorisation is currently the subject of the NEPSA\ud european project in which my thesis work is involved. This work is focused on the synthesis of AF\ud glucosylated derivatives with glucansucrases (GS) which catalyse the transfer of glucosyl residues\ud from sucrose to an exogenous molecule named acceptor.\ud We have demonstrated for the first time that AF is recognized as an acceptor by the GS from\ud Leuconostoc mesenteroides and Neisseria polysaccharea strains. The glucosylation products are\ud anhydro-D-fructo-glucooligosaccharides (AFGOS) which result from successive glucosyl transfers to\ud AF. Several AFGOS families of different structures are obtained owing to the specificity of the GS\ud used.\ud AFGOS present an anti-oxydant power as high as AF but no prebiotic effect. The reactivity of AF\ud was also studied in the case of oxime derivatization, and we developed a fast, quantitative and specific\ud conversion of AF and AFGOS.\ud Last, the production of AFGOS was optimised thanks to the control of the sucrose/AF molar ratio\ud and the total sugar concentration, thus reaching conversions comprised between 50 to 80 % owing to\ud the GS employed. In addition, the use of GS variants constructed by rational engineering enabled the\ud further increase of conversions. In order to isolate new enzymes improved for AF glucosylation and\ud which are generated by combinatorial engineering, a specific screening method based on the specific\ud AF reduction was developed

Sound and Posture: an Overview of Recent Findings

International audienceEven if it has been neglected for a long time, the sound and posture domain seemed to arouse an increasing interest in recent years. In the present position paper, we propose to present an overview of our recent findings on this field and to put them in perspective with the literature. We will bring evidence to support the view that spatial cues provided by auditory information can be integrated by human for a better postural control

The influence of horizontally rotating sound on standing balance

International audiencePostural control is known to be the result of the integration and processing of various sensory inputs by the central nervous system. Among the various afferent inputs, the role of auditory information in postural regulation has been addressed in relatively few studies, which led to conflicting results. The purpose of the present study was to investigate the influence of a rotating auditory stimulus, delivered by an immersive 3D sound spatialization system, on the standing posture of young subjects. The postural sway of 20 upright, blindfolded subjects was recorded using a force platform. Use of various sound source rotation velocities followed by sudden immobilization of the sound was compared with two control conditions: no sound and a stationary sound source. The experiment showed that subjects reduced their body sway amplitude and velocity in the presence of rotating sound compared with the control conditions. The faster the sound source was rotating, the greater the reduction in subject body sway.Moreover, disruption of subject postural regulation was observed as soon as the sound source was immobilized. These results suggest that auditory information cannot be neglected in postural control, and that it acts as additional information influencing postural regulation

Spatial Cues Provided by Sound Improve Postural Stabilization: Evidence of a Spatial Auditory Map?

International audienceIt has long been suggested that sound plays a role in the postural control process. Few studies however have explored sound and posture interactions. The present paper focuses on the specific impact of audition on posture, seeking to determine the attributes of sound that may be useful for postural purposes. We investigated the postural sway of young, healthy blindfolded subjects in two experiments involving different static auditory environments. In the first experiment, we compared effect on sway in a simple environment built from three static sound sources in two different rooms: a normal vs. an anechoic room. In the second experiment, the same auditory environment was enriched in various ways, including the ambisonics synthesis of a immersive environment, and subjects stood on two different surfaces: a foam vs. a normal surface. The results of both experiments suggest that the spatial cues provided by sound can be used to improve postural stability. The richer the auditory environment, the better this stabilization. We interpret these results by invoking the " spatial hearing map " theory: listeners build their own mental representation of their surrounding environment, which provides them with spatial landmarks that help them to better stabilize

Exploring the usability of sound strategies for guiding task: toward a generalization of sonification design

International audienceThis article aims at providing a new Parameter Mapping Sonification approach in order to facilitate and generalize sonification design for different applications. First a definition of the target as a con-cept that enables a general sonification strategy that is not limited to specific data types is given. This concept intends to facilitate the sepa-ration between sound and information to display. Rather than directly displaying data dimensions through the variation of a specific sound pa-rameter, the approach aims at displaying the distance between a given data value and the requested value. Then a taxonomy of sound strategies based on sound that allow the construction of several strategy types is presented. Finally, several sound strategies are evaluated with a user ex-periment and the taxonomy is discussed on the basis of user's guidance behavior during a guiding task

Icelandic herring-eating killer whales feed at night

This study was funded by an Icelandic Research Fund (i. Rannsóknasjóður, grant number 120248042) supported by a Marie Curie Fellowship.Herring-eating killer whales debilitate herring with underwater tail slaps and likely herd herring into tighter schools using a feeding-specific low-frequency pulsed call (‘herding’ call). Feeding on herring may be dependent upon daylight, as the whales use their white underside to help herd herring; however, feeding at night has not been investigated. The production of feeding-specific sounds provides an opportunity to use passive acoustic monitoring to investigate feeding behaviour at different times of day. We compared the acoustic behaviour of killer whales between day and night, using an autonomous recorder deployed in Iceland during winter. Based upon acoustic detection of underwater tail slaps used to feed upon herring we found that killer whales fed both at night and day: they spent 50% of their time at night and 73% of daytime feeding. Interestingly, there was a significant diel variation in acoustic behaviour. Herding calls were significantly associated with underwater tail slap rate and were recorded significantly more often at night, suggesting that in low-light conditions killer whales rely more on acoustics to herd herring. Communicative sounds were also related to underwater tail slap rate and produced at different rates during day and night. The capability to adapt feeding behaviour to different light conditions may be particularly relevant for predator species occurring in high latitudes during winter, when light availability is limited.Publisher PDFPeer reviewe

Phosphatidylinositol 3-Monophosphate Is Involved in Toxoplasma Apicoplast Biogenesis

Apicomplexan parasites cause devastating diseases including malaria and toxoplasmosis. They harbour a plastid-like, non-photosynthetic organelle of algal origin, the apicoplast, which fulfils critical functions for parasite survival. Because of its essential and original metabolic pathways, the apicoplast has become a target for the development of new anti-apicomplexan drugs. Here we show that the lipid phosphatidylinositol 3-monophosphate (PI3P) is involved in apicoplast biogenesis in Toxoplasma gondii. In yeast and mammalian cells, PI3P is concentrated on early endosomes and regulates trafficking of endosomal compartments. Imaging of PI3P in T. gondii showed that the lipid was associated with the apicoplast and apicoplast protein-shuttling vesicles. Interference with regular PI3P function by over-expression of a PI3P specific binding module in the parasite led to the accumulation of vesicles containing apicoplast peripheral membrane proteins around the apicoplast and, ultimately, to the loss of the organelle. Accordingly, inhibition of the PI3P-synthesising kinase interfered with apicoplast biogenesis. These findings point to an unexpected implication for this ubiquitous lipid and open new perspectives on how nuclear encoded proteins traffic to the apicoplast. This study also highlights the possibility of developing specific pharmacological inhibitors of the parasite PI3-kinase as novel anti-apicomplexan drugs

Polarization state of the optical near-field

The polarization state of the optical electromagnetic field lying several nanometers above complex dielectric structures reveals the intricate light-matter interaction that occurs in this near-field zone. This information can only be extracted from an analysis of the polarization state of the detected light in the near-field. These polarization states can be calculated by different numerical methods well-suited to near--field optics. In this paper, we apply two different techniques (Localized Green Function Method and Differential Theory of Gratings) to separate each polarisation component associated with both electric and magnetic optical near-fields produced by nanometer sized objects. The analysis is carried out in two stages: in the first stage, we use a simple dipolar model to achieve insight into the physical origin of the near-field polarization state. In the second stage, we calculate accurate numerical field maps, simulating experimental near-field light detection, to supplement the data produced by analytical models. We conclude this study by demonstrating the role played by the near-field polarization in the formation of the local density of states.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.