Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The SARS-Cov-2 covid-19 pandemic outbreak continues to claim victims to this day. As the vaccine is ineffective for completely eradicating the virus, there is an urgent need to look at other solutions, including developing antivirals.
Lipopeptides, particularly surfactin, have been recognized for their antiviral activity against several enveloped viruses. However, a better comprehension of their mode of action is necessary to develop antivirals based on those lipopeptides. Moreover, studying several variants allows a better insight into the relationships between the structure of lipopeptides and their antiviral activity.
In this work, a biophysical approach involving the use of liposomes as membrane biomimetic models was used. Four liposome models were created, including one aiming to mimic the host cell plasma membrane and one seeking to mimic the viral membrane.
The effect of surfactin variants on membrane permeability and fluidity was analyzed on these biomimetic liposomes.
Several mechanisms have been suggested to explain the surfactins action on liposomes. It was hypothesized that some variants had two-stage effects on membranes incorporating lipids such as cholesterol and PE. These lipids, potentially at the origin of this biphasic mechanism, could make the membrane more resistant to high surfactin concentrations. It was also hypothesized that the structure of some variants might influence the toxicity of surfactins on the membranes. Finally, it was observed that the studied variants might be more toxic on biological mimicking membranes than viral ones. Further studies are nevertheless mandatory to assert all these hypotheses.

Coronavirus --- Liposomes --- Characterisation --- Biophysics --- Membranes --- Surfactin --- Lipopeptides --- In vitro --- Sciences du vivant > Multidisciplinaire, généralités & autres

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

The plant plasma membrane is a very complex structure, mainly composed of lipids and proteins, that determines cell boundaries and controls the entry and exit of molecules. In plants, the plasma membrane is involved in the perception of elicitors, such as surfactin. This molecule is able to induce the plant defense response which makes it a potential alternative to conventional pesticides.
The molecular mechanism behind this perception process is little-known. To investigate this process, biomimetic models, including lipid monolayers, supported bilayers and liposomes, and biological models, including protoplasts are required. A protoplast is a cell which is delimited by the biological plasma membrane but that does no longer have its cell wall, it is a reliable model because it has a composition similar to the biological membrane.
This master's thesis aimed to develop and optimize the isolation of tomato root protoplasts and to optimize isothermal titration calorimetry (ITC) parameters for measuring the thermodynamics of binding events with protoplasts. After these optimization steps, interaction of protoplasts with surfactin was thermodynamically characterized with ITC and their reactivity in terms of defense response in presence of surfactin was analyzed by reactive oxygen species measurement.
First, to optimize the isolation of tomato root protoplasts, the effect of four factors, including time and speed of centrifugation, the age of roots, the time of incubation with enzymes and the agitation speed during the incubation with enzymes, on protoplast production yield and percentage of viability was investigated. It was shown that all parameters had an influence on protoplast production yield and the protoplast suspension with the highest yield was obtained from 7-day-old roots that were incubated for 17 hours without agitation and that were puri ed with a centrifugation at 600 rcf for 6 minutes. It was also shown that flow cytometry on tomato root protoplasts is complicated due to the high number of debris in protoplast suspension. Its use would require an improvement of the puri fication steps of the protoplast suspension.
Secondly, it was determined that the best con gfiuration for the ITC measurements is to put the protoplasts in the measuring cell with a low agitation. In this case there was no decrease of the protoplast concentration and of their percentage of viability during a measurement. In presence of surfactin, a binding event was observed. However, optimization of the concentration of protoplasts is still required in order to obtain an optimal pro le of heat flow for the determination of the thermodynamic parameters.
Production of reactive oxygen species (ROS) was also observed in presence of surfactin con firming
the good reactivity of protoplasts in terms of defense response.
In conclusion, this thesis paves the way to produce and use root protoplasts in biophysical experiments
such as ITC to better understand the perception of elicitors in plants. La membrane plasmique végétale est une structure très complexe, principalement composée de lipides et de protéines, qui détermine les limites de la cellule et qui contrôle l’entrée et la sortie de molécules. Chez les plantes, la membrane plasmique est impliquée dans la perception d’éliciteurs, tel que la surfactine, qui est capable d’induire la réponse de défense dans la plante et qui en fait une alternative potentielle aux pesticides conventionnels. Le mécanisme moléculaire à l’origine de ce processus de perception est peu connu. Pour étudier ce processus, des modèles biomimétiques, tels que les monocouches lipidiques, les bicouches lipidiques supportées et les liposomes, et des modèles biologiques, tel que les protoplastes, sont nécessaires. Un protoplaste est une cellule qui est délimitée par la membrane plasmique biologique mais qui ne dispose plus de sa paroi cellulaire. C’est un modèle fiable parce qu’il a une composition similaire à celle de la membrane biologique.
Cette thèse a pour but de développer et d’optimiser l’isolation des protoplastes de racines de tomates ainsi que d’optimiser les paramètres de titrage calorimétrique isotherme (ITC) pour mesurer la thermodynamique des événements dûs à une interaction avec les protoplastes. Après ces étapes d’optimisation, l’interaction des protoplastes avec la surfactine a été caractérisée thermodynamiquement avec l’ITC et leur réactivité en termes de réponse de défense en présence de surfactine a été analysée par la mesure des espèces réactives de l’oxygène.
Premièrement, pour optimiser l’isolation des protoplastes de racines de tomates, l’effet de quatre facteurs, dont le temps et la vitesse de centrifugation, l’âge des racines, le temps d’incubation avec les enzymes et la vitesse d’agitation pendant l’incubation avec les enzymes, sur le rendement en protoplastes et le pourcentage de viabilité a été´etudié. Il a été démontré que tous les paramètres avaient une influence sur le rendement en protoplastes et la suspension de protoplastes ayant le rendement le plus élevé a été obtenue à partir de racines de 7 jours qui ont été incubées pendant 17 heures sans agitation et qui ont été purifiées par une centrifugation à 600 rcf pendant 6 minutes. L’utilisation de la cytométrie de flux s’est révélée difficile suite à la présence d’un nombre importants de débris racinaires dans la suspension de protoplastes. Pour pouvoir employer la cytométrie, une amélioration des étapes de purification de la suspension de protoplastes est requise.
Ensuite, il a été déterminé que la meilleure configuration pour les mesures à l’aide de l’ITC est de placer les protoplastes dans la cellule de mesure avec une faible agitation. Dans ce cas, il n’y a eu aucune diminution de la concentration en protoplastes et de leur pourcentage de viabilité au
cours de la mesure. En présence de surfactine, un événement dû à une interaction a été observé.
Cependant, l’optimisation de la concentration en protoplastes est toujours nécessaire afin d’obtenir un profil optimal du flux thermique pour la détermination des paramètres thermodynamiques.
La production d’espèces réactives de l’oxygène (ROS) a également été observée en présence de surfactine, ce qui a permis de confirmer que les protoplastes ont une bonne réactivité en termes de
réponse de défense.
En conclusion, ce mémoire pose les bases pour l’obtention et l’utilisation de protoplastes de racines dans des expériences biophysiques tel que l’ITC, afin de mieux comprendre la perception des éliciteurs chez les plantes.

Root protoplasts --- Optimization --- Isothermal Titration Calorimetry --- Surfactin --- Reactive Oxygen Species --- Protoplaste racinaire --- Optimisation --- Titrage Calorimétrique Isotherme --- Surfactine --- Espèces Réactives de l'Oxygène --- Physique, chimie, mathématiques & sciences de la terre > Chimie --- Sciences du vivant > Biochimie, biophysique & biologie moléculaire --- Sciences du vivant > Biologie végétale (sciences végétales, sylviculture, mycologie...)

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Very few materials have attracted so much attention in recent years, both from researchers and industry, as layered double hydroxides (LDHs) have. LDHs, which are also referred to as anionic clays or hydrotalcites, are a wide class of inorganic ionic lamellar clay materials consisting of alternately stacked positively charged metal hydroxide layers with intercalated charge-balancing anions in hydrated interlayer regions. Their unique properties, such as their extremely high versatility in chemical composition and intercalation ability, extraordinary tuneability in composition as well as morphology, good biocompatibility and high anion exchangeability, have triggered immense interdisciplinary interest for their use in many different fields of chemistry, biology, medicine, and physics. Indeed, the applications of LDHs are constantly growing: LDHs, in the form of aggregated lamellar clusters, exfoliated single-layer nanosheets, or hierarchical films of interconnected nanoplatelets, can be effectively used as nanoscale vehicles in drug delivery, heterogeneous catalysts and supports for molecular catalysts, ion exchangers and adsorbents, solid electrolytes or fillers in electrochemistry, for the fabrication of superhydrophobic surfaces, water treatment and purification, and the synthesis of functional thin films. This book gathers the contributions to the Special Issue “Layered Double Hydroxides” of Crystals, which includes two review articles and seven research papers.

layered double hydroxide --- memory effect --- rare earth --- europium --- 1,3,5-benzenetricarboxylic acid --- alginate beads --- green sorbent --- selective adsorption --- heavy metals --- tetracycline --- metal hydroxides --- layered double hydroxides --- removal --- water sample --- Bacillus subtilis --- surfactin --- quantitative analysis --- fermentation --- growth phase --- cellular biology --- catalysis --- DNA --- drug delivery --- hydrotalcite --- osteogenesis --- photocatalysis --- RNA. --- antimonate uptake --- mine water --- brandholzite --- zincalstibite --- iron precursor --- acidic residual solution --- LDH synthesis --- Mo(VI) adsorption --- resveratrol --- solid lipid nanoparticles --- endurance exercise --- mitochondrial nutrients --- mitochondrial quality control --- origin of life --- layer double hydroxide --- synthetic biology --- bioinspired devices --- biosensors --- bioanalysis --- n/a