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See detailHomology modeling and in vivo functional characterization of the zinc permeation pathway in a heavy metal P-type ATPase
Lekeux, Gilles ULiege; Crowet, Jean-Marc; Nouet, Cécile ULiege et al

in Journal of Experimental Botany (in press)

The P1B ATPase Heavy Metal ATPase 4 (HMA4) is responsible for zinc and cadmium translocation from roots to shoots in the plant Arabidopsis thaliana. It couples ATP hydrolysis to cytosolic domain movements ... [more ▼]

The P1B ATPase Heavy Metal ATPase 4 (HMA4) is responsible for zinc and cadmium translocation from roots to shoots in the plant Arabidopsis thaliana. It couples ATP hydrolysis to cytosolic domain movements enabling metal transport across the membrane. Thanks to high conservation level within the P-type ATPase family, the role of the HMA4 cytoplasmic catalytic domains can be inferred from well characterized pumps. In contrast, the function of its terminal cytosolic extensions as well as the metal permeation mechanism through the membrane remains elusive. Here, homology modeling of the HMA4 transmembrane region was conducted based on the crystal structure of a ZntA bacterial homolog. The analysis highlighted amino acids forming a metal permeation pathway, whose importance was subsequently investigated functionally through mutagenesis and complementation experiments in plants. Although the zinc pathway displayed overall conservation among the two proteins, significant differences were observed, especially in the entrance area with altered electronegativity and the presence of a salt bridge/H-bond network. The analysis also newly identified amino acids whose mutation results in total or partial loss of the protein function. In addition, comparison of zinc and cadmium accumulation in shoots of A. thaliana complemented lines revealed a number of HMA4 mutants exhibiting different abilities in zinc and cadmium translocation. These observations could be instrumental to design low cadmium accumulating crops, hence decreasing human cadmium exposure . [less ▲]

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See detailNew insights into the biosynthesis of esterified oxylipins and their involvement in plant defense and developmental mechanisms
Genva, Manon ULiege; Obounou Akong, Firmin ULiege; Andersson, Mats X. et al

in Phytochemistry Reviews (2018)

Plant oxylipins produced following oxidation of unsaturated fatty acids are structurally diverse metabolites that play crucial developmental and defensive roles. Whereas free oxylipins are well studied ... [more ▼]

Plant oxylipins produced following oxidation of unsaturated fatty acids are structurally diverse metabolites that play crucial developmental and defensive roles. Whereas free oxylipins are well studied, oxylipins esterified in complex lipids such as galacto- and phospholipids are thought to be rare and have unclear roles. In the last few years, new analytical methods have been developed, leading to the discovery of many esterified oxylipins in a variety of plant species. This suggests that these molecules may be ubiquitous plant metabolites. While their precise functions are unclear, esterified oxylipins seem to play important roles in plant development and defense. This review focuses on new insights regarding diversity, biosynthesis and function of those interesting and understudied molecules. [less ▲]

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See detailOxylipins are involved in plant protections processes and are potential biocontrol agents
Deboever, Estelle ULiege; Genva, Manon ULiege; Deleu, Magali ULiege et al

Conference (2018, September 27)

Nowadays, biopesticides have emerged as a main alternative to conventional agriculture. In this context, plant oxylipins, a vast and diverse family of secondary metabolites originated from polyunsaturated ... [more ▼]

Nowadays, biopesticides have emerged as a main alternative to conventional agriculture. In this context, plant oxylipins, a vast and diverse family of secondary metabolites originated from polyunsaturated fatty acids (PUFAs), appear to be crucial agents in plant defence mechanisms. Among plant oxylipins, the 13-hydroperoxy oxylipins (13-HPO) constitute key intermediate oxylipins (KIOs) as they can be converted into jasmonic acid, OPDA, dn-OPDA or traumatic acid, well-characterized components involved in plant resistance mechanisms [1][2]. Their presumed functions include direct antimicrobial effect, stimulation of plant defence gene expression, and/or regulation of plant cell death [3]. Otherwise, OPDA and dn-OPDA were also found esterified in more complex structures such as galactolipids. Those compounds are called arabidopsides. However, the precise contribution of each of those molecules in plant defence remains unknown. The first part of this study aims to understand the oxylipins action mechanisms and especially their membrane activities. As arabidopsides are produced under stress and localized at the chloroplast membranes, their interactions with those were studied using biomimetic membranes via a complementary in silico informatics and in vitro biophysical approaches. On the other hand, as KIOs are found in the literature to be potential biocontrol agents, there effect on different pathogens of agronomic interest were studied in vitro, by the same approach. As far as arabidopsides are concerned, results show that they possess different interfacial properties compared to major chloroplast lipids, which they are produced from. Arabidopsides modify the fluidity and permeabilize chloroplast membranes. As chloroplast membrane lipid composition is essential to its photosynthetic ability, such changes in its composition under stress will affect its function. Concerning KIOs, they seem to interact with pathogens plasma membranes. Indeed, in vitro assays show that KIOs can hinder growth of some plant microbial pathogens, with differences between strains and KIOs forms. [less ▲]

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See detailHow could the herbicidal effects of selected essential oil compounds be related to their membrane activity ?
Lins, Laurence ULiege; Bettaieb, Ines; Dal Maso, Simon ULiege et al

Poster (2018, September 25)

The European legislation on plant protection products (PPP) is about to undergo important changes in the coming years. The chemical PPP destined to be removed from the European market are responsible for ... [more ▼]

The European legislation on plant protection products (PPP) is about to undergo important changes in the coming years. The chemical PPP destined to be removed from the European market are responsible for the appearance of resistance phenomena to plants pests. It is therefore necessary to explore new alternatives, one of them being the search for natural herbicides. Essential oils (EO) could provide a welcome alternative due to their proven activity as PPP. Even if these compounds seem to have a bright future as PPP, their activity is mainly approached through empirical observations. EO are also a complex mix of of different molecules that could act individually or in synergy. Particularly, very little is known when it comes to molecular mechanisms of action and the relations between structure and activity of the active compounds. This study aims to investigate the structure/activity relationships of some EO molecules, among which cinnamaldehyde (CIN) from cinnamon and citronellal and citronellol from lemongrass. Due to their lipophilic properties, EO tend to interact with one or more of the layers found in the outer plant tissues, among which the cell membranes. For cinnalmaldehyde (and other EO compounds), it has been shown that they are able to interact with bacterial phospholipids and induce change in lipid organization (fluidity, packing,..) on model lipid monolayers (Nowotarska et al, 2014). Citronnellol was notably shown to displace cholesterol from its phospholipid complexes (Lange, Y et al, 2009). However, nothing is known about any interaction with lipids specific to plant plasma membrane (PPM). In this study, we analyzed the effects of the above three EO compounds on model PPM by complementary in vitro and in silico biophysical approaches. We showed that the three compounds have differential effects on plant lipids and different herbicidal properties on plantae. While part of the herbicidal activity could be related to membrane perturbation, some clues remain to be elucidated. Future studies at a molecular point of view would help to better decipher the herbicidal action involving the membrane, other outer plant tissues such as the cuticule and/or and a potential effect on EO compounds on proteins or genomic DNA, as it was shown for CIN on E. Coli (He, TF et al, 2018). [less ▲]

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See detailThe molecular mechanisms of membrane tethering at plasmodesmata intercellular junctions
Petit, Jules ULiege; Brault, Marie; Immel, Françoise et al

Poster (2018, September)

Intercellular communication is critical for multicellularity. It coordinates the activities within individual cells to support the function of an organism as a whole. Plants have developed remarkable ... [more ▼]

Intercellular communication is critical for multicellularity. It coordinates the activities within individual cells to support the function of an organism as a whole. Plants have developed remarkable cellular machines -the Plasmodesmata (PD) pores- which interconnect every single cell within the plant body, establishing direct membrane and cytoplasmic continuity, a situation unique to plants. PD are indispensable for plant life hence human health. They control the flux of molecules between cells and are decisive for development, environmental adaptation and defence signalling. A striking feature of PD organisation, setting them apart from animal cell junctions, is a strand of endoplasmic reticulum (ER) running through the pore, tethered extremely tight (~10nm) to the plasma membrane (PM) by unidentified “spokes”. To date the function of ER-PM contacts at PD remains a complete enigma. We don’t know the molecular mechanisms controlling this highly specialized membrane junctions. Our work focuses on investigating the structure/function of the C2 domains of the Multiple C2 domains and Transmembrane region Proteins (MCTPs) family, which are candidate ER-PM tethers. Sequence analysis of the MCTPs was performed to delimit the C2 domains and molecular modelling was used to build accurate 3D models that were used for molecular dynamic simulations. Our results suggest the ability of C2 domains to dock onto biomimetic lipid bilayers, in an anionic lipid-dependent manner, as a result of electrostatic interactions between basic amino residues and lipid polar heads. [less ▲]

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See detailHow different serols contribute to cytotoxic action of sea cucumber saponins
Claereboudt, Emily ULiege; Eeckhaut, Igor; Deleu, Magali ULiege et al

Poster (2018, May 24)

Saponins form a diverse class of secondary metabolites found in both plants and some marine invertebrates. Holothuroids, or sea cucumbers, produce these molecules as a chemical defense against predators ... [more ▼]

Saponins form a diverse class of secondary metabolites found in both plants and some marine invertebrates. Holothuroids, or sea cucumbers, produce these molecules as a chemical defense against predators and parasites, but interestingly, tolerate the cytotoxic nature of these chemicals. This tolerance is poorly understood. The aim of this study was therefore to elucidate the mechanisms behind the tolerance of holothuroid cells to the cytotoxic saponins (e.g. Frondoside A) they produce. This investigation was conducted using a suite of complementary biophysical tools, firstly using in vitro techniques such as Isothermal Titration Calorimetry (ITC) and calcein leakage experiments, for measuring interactions between lipid models of various compositions and the saponin Frondoside A, then using in silico approaches such as docking methods and insertion into implicit lipid bilayers, to provide a molecular point of view on our observations. Interactions between Frondoside A and cholesterol were more favorable than those with the holothuroid Δ7 and Δ9(11) sterols. Liposomes containing cholesterol resulted in exothermic interactions with the holothuroid saponin Frondoside A whereas liposomes containing the Δ7 sterol resulted in endothermic interactions. Lipid phase simulations using settings previously developed for plant saponins revealed that the holothuroid saponin Frondoside A has an agglomerating effect on cholesterol domains, similar to that previously observed for the plant saponin α-Hederin. However, when interacting with the Δ7 sterols, the sterol domains were fragmented into small clusters. A significantly lower leakage was observed with liposomes containing the Δ7 holothuroid sterol than that with liposomes containing cholesterol. Our results suggest that the structural peculiarities of holothuroid sterols provide the organisms with a mechanism to mitigate the sterol-agglomerating effect of saponins on the cell membranes, and therefore to protect sea cucumber cells from the cytotoxicity of the saponins they produce. [less ▲]

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See detailInteractions of allelochemicals with plant plasma membrane: a case study with alkaloids from barley
Lebecque, Simon ULiege; Crowet, Jean-Marc; du Jardin, Patrick ULiege et al

Poster (2018, April)

Allelopathy is defined as “any direct or indirect harmful effect by one plant on another through production of chemical compounds that escape into the environment” (Rice, 1974).This phenomenon is seen as ... [more ▼]

Allelopathy is defined as “any direct or indirect harmful effect by one plant on another through production of chemical compounds that escape into the environment” (Rice, 1974).This phenomenon is seen as a potential tool for weeds management within the framework of sustainable agriculture. While many studies investigated the mode of action of various allelochemicals (molecules emitted by allelopathic plants), little attention was given to their initial contact with the plant plasma membrane. In our work, this key step is explored for two alkaloids, gramine and hordenine, that are allelochemicals produced by barley. [less ▲]

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See detailHow different sterols contribute to saponin tolerant plasma membranes in sea cucumbers
Claereboudt, Emily ULiege; Deleu, Magali ULiege; Lins, Laurence ULiege et al

Scientific conference (2018, March 07)

ABSTRACT. Sea cucumbers produce saponins as a chemical defense mechanism, however their cells can tolerate the cytotoxic nature of these chemicals. To elucidate the molecular mechanisms behind this ... [more ▼]

ABSTRACT. Sea cucumbers produce saponins as a chemical defense mechanism, however their cells can tolerate the cytotoxic nature of these chemicals. To elucidate the molecular mechanisms behind this tolerance a suite of complementary biophysical tools was used, firstly using liposomes for in vitro techniques then using in silico approaches for a molecular-level insight. The holothuroid saponin Frondoside A, caused significantly less permeabilization in liposomes containing a Δ7 holothuroid sterol than those containing cholesterol and resulted in endothermic interactions versus exothermic interactions with cholesterol containing liposomes. Lipid phases simulations revealed that Frondoside A has an agglomerating effect on cholesterol domains, however, induced small irregular Δ7 sterol clusters. Our results suggest that the structural peculiarities of holothuroid sterols provide sea cucumbers with a mechanism to mitigate the sterol-agglomerating effect of saponins, and therefore to protect their cells from the cytotoxicity of the saponins they produce. [less ▲]

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See detailUse of molecular dynamics simulations to study the interactions between barley allelochemicals and plant plasma membrane
Lebecque, Simon ULiege; Crowet, Jean-Marc; du Jardin, Patrick ULiege et al

Poster (2018, March)

Gramine and hordenine, two alkaloids produced by barley, were shown to inhibit the growth of a common weed (Matricaria recutita L.). This feature could be useful in order to reach a more sustainable weeds ... [more ▼]

Gramine and hordenine, two alkaloids produced by barley, were shown to inhibit the growth of a common weed (Matricaria recutita L.). This feature could be useful in order to reach a more sustainable weeds management. In vitro experiments have proven that both molecules do interact with lipid bilayers (made of a phosphatidylglycerol (PG) lipid) mimicking plant plasma membranes and are able to modify some of their properties. Moreover, gramine was shown to be more effective than hordenine in both inhibiting weeds growth and altering lipid bilayers properties, suggesting that interactions with membranes could be linked to their mode of action. Molecular dynamics (MD) simulations are carried out in order to get an insight into the molecular mechanisms that underlie these interactions with model membranes and to discriminate between gramine behavior and hordenine behavior. [less ▲]

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See detailAnalyse de séquence et dynamique moléculaire pour révéler le rôle des domaines C2 des protéines MCTPs impliquées dans la connexion membranaire des plasmodesmes chez les plantes
Petit, Jules ULiege; Crowet, Jean-Marc; Deleu, Magali ULiege et al

Conference (2018, January 19)

Chez les organismes multicellulaires, la communication de cellule à cellule est essentielle à la coordination des activités cellulaires pour le fonctionnement de l’organisme dans son entièreté. Les ... [more ▼]

Chez les organismes multicellulaires, la communication de cellule à cellule est essentielle à la coordination des activités cellulaires pour le fonctionnement de l’organisme dans son entièreté. Les plantes terrestres ont développé des systèmes tout à fait particuliers, les plasmodesmes (PD), qui traversent la paroi et permettent le transfert contrôlé de molécules. La structure et l’organisation membranaire au sein des PD est unique : la membrane plasmique forme un manchon contre la paroi, établissant une continuité cytosolique et permettant le passage du desmotubule, qui est une continuité du réticulum endoplasmique. Les deux membranes traversant le PD sont très intimement accolées (~10nm d’espacement) et connectées par des liens moléculaires protéiques. Les PD sont donc des sites de contacts membranaires spécialisés qui initient et relaient de nombreuses voies de signalisation. Les mécanismes moléculaires associés à ces contacts et à la régulation des PD restent néanmoins largement sous-étudiés. Cependant, leur spécificité d’action et de structure ainsi que leur composition lipidique particulière supportent la présence d’une population protéique propre. Très récemment, le groupe de recherche de E. Bayer a découvert une importante famille de protéine, les MCTPs (Multiple C2 domains and Transmembrane region Proteins), dont les membres sont localisés et enrichis aux PD. Les protéines MCTPs ont une topologie similaire à des protéines "tether" connues qui lient la membrane plasmique et le réticulum endoplasmique chez les animaux et chez les plantes (Extended-Synaptotagmins, Synaptotagmins) : plusieurs domaines C2, connus pour interagir avec des lipides membranaires, du côté N-terminal, et une région transmembranaire ancrée dans le réticulum endoplasmique, du côté C-terminal. Ils sont donc des candidats intéressants dans cette connexion entre les membranes. Notre travail est axé sur la prédiction du docking de ces domaines C2 individuels avec la membrane plasmique des plantes et la compréhension de leurs interactions spécifiques avec les lipides. Dans un premier temps, une analyse de la séquence a permis une délimitation fine de chaque domaine C2 des protéines MCTP afin de pouvoir construire des modèles 3D par homologie de structure. Ensuite, des simulations de dynamique moléculaire ont permis de prédire la capacité d’interaction de chaque domaine et d’obtenir des informations, à l’échelle atomique, sur les interactions. Les résultats semblent indiquer une affinité de certains domaines pour les lipides anioniques de la membrane plasmique des plantes (phosphatidylsérine, phosphatidylinositol-4-phosphate). De plus, des résultats préliminaires concernant la possibilité de coordination d’ions calciums par certains domaines – une autre caractéristique connue des domaines C2 – suggèrent que les différents domaines C2 des MCTPs ont des fonctions différentes et spécifiques, compatible avec l’idée de haute plasticité des sites de contact membranaire PD. [less ▲]

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See detailEvaluation des interactions entre les arabidopsides et les lipides de la membrane plasmique des plantes
Genva, Manon ULiege; Deleu, Magali ULiege; Andersson, Mats X. et al

Poster (2018, January 19)

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See detailInsight into the self assembly properties of peptergents: a molecular dynamics simulation study
Crowet, Jean Marc; Nasir, Mehmet Nail; Dony, Nicolas et al

in International Journal of Molecular Sciences (2018)

By manipulating the various physico-chemical properties of amino acids, design of peptides with specific self-assembling properties has been emerging since more than a decade. In this context, short ... [more ▼]

By manipulating the various physico-chemical properties of amino acids, design of peptides with specific self-assembling properties has been emerging since more than a decade. In this context, short peptides possessing detergent properties (so-called “peptergents”) have been developed to self-assemble into well-ordered nanostructures that can stabilize membrane proteins for crystallization. In this study, the peptide with “peptergency” properties, called ADA8 extensively described by Tao et al., is studied by molecular dynamic simulations for its self-assembling properties in different conditions. In water, it spontaneously form beta sheets with a β barrel-like structure. We next simulated the interaction of this peptide with a membrane protein, the bacteriorhodopsin, in the presence or absence of a micelle of dodecylphosphocholine. According to the literature, the peptergent ADA8 is thought to generate a belt of β structures around the hydrophobic helical domain that could help stabilize purified membrane proteins. Molecular dynamic simulations are here used to image this mechanism and to provide further molecular details for the replacement of detergent molecules around the protein. In addition, we generalized this behavior by designing an amphipathic peptide with beta propensity, called ABZ12. Both peptides are able to surround the membrane protein and displace surfactant molecules. To our best knowledge, this is the first molecular mechanism proposed for ''peptergency''. [less ▲]

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See detailInteraction between the barley allelochemical compounds gramine and hordenine and artificial lipid bilayers mimicking the plant plasma membrane
Lebecque, Simon ULiege; Crowet, Jean-Marc; Lins, Laurence ULiege et al

in Scientific Reports (2018), 8

Some plants affect the development of neighbouring plants by releasing secondary metabolites into their environment. This phenomenon is known as allelopathy and is a potential tool for weed management ... [more ▼]

Some plants affect the development of neighbouring plants by releasing secondary metabolites into their environment. This phenomenon is known as allelopathy and is a potential tool for weed management within the framework of sustainable agriculture. While many studies have investigated the mode of action of various allelochemicals (molecules emitted by allelopathic plants), little attention has been paid to their initial contact with the plant plasma membrane (PPM). In this paper, this key step is explored for two alkaloids, gramine and hordenine, that are allelochemicals from barley. Using in vitro bioassays, we first showed that gramine has a greater toxicity than hordenine towards a weed commonly found in northern countries (Matricaria recutita L.). Then, isothermal titration calorimetry was used to show that these alkaloids spontaneously interact with lipid bilayers that mimic the PPM. The greater impact of gramine on the thermotropic behaviour of lipids compared to hordenine was established by means of infrared spectroscopy. Finally, the molecular mechanisms of these interactions were explored with molecular dynamics simulations. The good correlation between phytotoxicity and the ability to disturb lipid bilayers is discussed. In this study, biophysical tools were used for the first time to investigate the interactions of allelochemicals with artificial PPM. [less ▲]

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See detailHow different serols contribute to saponin tolerant plasma membranes in sea cucumbers
Claereboudt, Emily ULiege; Eeckhaut, Igor; Lins, Laurence ULiege et al

in Scientific Reports (2018), 8

Sea cucumbers produce saponins as a chemical defense mechanism, however their cells can tolerate the cytotoxic nature of these chemicals. To elucidate the molecular mechanisms behind this tolerance a ... [more ▼]

Sea cucumbers produce saponins as a chemical defense mechanism, however their cells can tolerate the cytotoxic nature of these chemicals. To elucidate the molecular mechanisms behind this tolerance a suite of complementary biophysical tools was used, firstly using liposomes for in vitro techniques then using in silico approaches for a molecular-level insight. The holothuroid saponin Frondoside A, caused significantly less permeabilization in liposomes containing a Δ7 holothuroid sterol than those containing cholesterol and resulted in endothermic interactions versus exothermic interactions with cholesterol containing liposomes. Lipid phases simulations revealed that Frondoside A has an agglomerating effect on cholesterol domains, however, induced small irregular Δ7 sterol clusters. Our results suggest that the structural peculiarities of holothuroid sterols provide sea cucumbers with a mechanism to mitigate the sterol-agglomerating effect of saponins, and therefore to protect their cells from the cytotoxicity of the saponins they produce. [less ▲]

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See detailSynthetic rhamnolipid bolaforms trigger an innate immune response in Arabidopsis thaliana
Luzuriaga-Loaiza, Patricio; Schellenberger, Romain; De Gaetano, Yannick et al

in Scientific Reports (2018), 8

Stimulation of plant innate immunity by natural and synthetic elicitors is a promising alternative to conventional pesticides for a more sustainable agriculture. Sugar-based bolaamphiphiles are known for ... [more ▼]

Stimulation of plant innate immunity by natural and synthetic elicitors is a promising alternative to conventional pesticides for a more sustainable agriculture. Sugar-based bolaamphiphiles are known for their biocompatibility, biodegradability and low toxicity. In this work, we show that Synthetic Rhamnolipid Bolaforms (SRBs) that have been synthesized by green chemistry trigger Arabidopsis innate immunity. Using structure-function analysis, we demonstrate that SRBs, depending on the acyl chain length, differentially activate early and late immunity-related plant defense responses and provide local increase in resistance to plant pathogenic bacteria. Our biophysical data suggest that SRBs can interact with plant biomimetic plasma membrane and open the possibility of a lipid driven process for plant-triggered immunity by SRBs. [less ▲]

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See detailEvaluation of interactions between arabidopsides and plant plasma membrane lipids
Genva, Manon ULiege; Deleu, Magali ULiege; Andersson, Mats X. et al

Poster (2018)

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