Modulation of plant plasma membrane structure by exogenous fatty acid hydroperoxide is a potential perception mechanism for their eliciting activity

Oxylipins are lipid-derived molecules that are ubiquitous in eukaryotes and whose functions in plant physiology have been widely reported. They appear to play a major role in plant immunity by orchestrating reactive oxygen species (ROS) and hormone-dependent signalling pathways. The present work focuses on the specific case of fatty acid hydroperoxides (HPOs). Although some studies report their potential use as exogenous biocontrol agents for plant protection, evaluation of their efficiency in planta is lacking and no information is available about their mechanism of action. In this study, the potential of 13(S)-hydroperoxy-(9Z, 11E)-octadecadienoic acid (13-HPOD) and 13(S)-hydroperoxy-(9Z, 11E, 15Z)-octadecatrienoic acid (13-HPOT), as plant defence elicitors and the underlying mechanism of action is investigated. Arabidopsis thaliana leaf resistance to Botrytis cinerea was observed after root application with HPOs. They also activate early immunity-related defence responses, like ROS. As previous studies have demonstrated their ability to interact with plant plasma membranes (PPM), we have further investigated the effects of HPOs on biomimetic PPM structure using complementary biophysics tools. Results show that HPO insertion into PPM impacts its global structure without solubilizing it. The relationship between biological assays and biophysical analysis suggests that lipid amphiphilic elicitors that directly act on membrane lipids might trigger early plant defence events.

Sitosterol and glucosylceramide cooperative transversal and lateral uneven distribution in plant membranes

The properties of biomembranes depend on the presence, local structure and relative distribution assumed by the thousands of components it is made of. As for animal cells, plant membranes have been demonstrated to be organized in subdomains with different persistence lengths and times. In plant cells, sitosterol has been demonstrated to confer to phospholipid membranes a more ordered structure while among lipids, glycosphingolipids are claimed to form rafts where they tightly pack with sterols. Glucosylceramides are glycosphingolipids involved in plant signalling and are essential for viability of cells and whole plant. The glucosylceramide-sitosterol structural coupling within PLPC membranes is here investigated by Langmuir films, in silico simulations and neutron reflectometry, unveiling that a strong direct interaction between the two molecules exists and governs their lateral and transversal distribution within membrane leaflets. The understanding of the driving forces governing specific molecules clustering and segregation in subdomains, such as glucosylceramide and sitosterol, have an impact on the mechanical properties of biomembranes and could reflect in the other membrane molecules partitioning and activity.

Essential Oil-Based Bioherbicides: Human Health Risks Analysis

In recent years, the development of new bio-based products for biocontrol has been gaining importance as it contributes to reducing the use of synthetic herbicides in agriculture. Conventional herbicides (i.e., the ones with synthetic molecules) can lead to adverse effects such as human diseases (cancers, neurodegenerative diseases, reproductive perturbations, etc.) but also to disturbing the environment because of their drift in the air, transport throughout aquatic systems and persistence across different environments. The use of natural molecules seems to be a very good alternative for maintaining productive agriculture but without the negative side effects of synthetic herbicides. In this context, essential oils and their components are increasingly studied in order to produce several categories of biopesticides thanks to their well-known biocidal activities. However, these molecules can also be potentially hazardous to humans and the environment. This article reviews the state of the literature and regulations with regard to the potential risks related to the use of essential oils as bioherbicides in agricultural and horticultural applications.

A compartmentalized microsystem helps understanding the uptake of benzo[a]pyrene by fungi during soil bioremediation processes

Hydrophobic organic soil contaminants such as polycyclic aromatic hydrocarbons (PAH) are poorly mobile in the aqueous phase and tend to sorb to the soil matrix, resulting in low bioavailability. Some filamentous fungi are efficient in degrading this kind of pollutants. However, the mechanism of mobilization of hydrophobic compounds by non-motile microorganisms such as filamentous fungi needs investigations to improve pollutant bioavailability and bioremediation efficiency. Usual homogeneous media for microbial growth in the lab are poorly suited to model the soil, which is a compartmentalized and heterogeneous habitat. A microfluidic device was designed to implement a compartmentalization of the fungal inoculum and the source of the pollutant benzo[a]pyrene (BaP) as a deposit of solid crystals in order to gain a further insight into the mechanisms involved in the access to the contaminant and its uptake in soils. Thus in this device, two chambers are connected by an array of parallel microchannels that are wide enough to allow individual hyphae to grow through them. Macro-cultures of Talaromyces helicus in direct contact with BaP have shown its uptake and intracellular storage in lipid bodies despite the low propensity of BaP to cross aqueous phases as shown by simulation. Observations of T. helicus in the microfluidic device through laser scanning confocal microscopy indicate preferential uptake of BaP at a close range and through contact with the cell wall. However faint staining of some hyphae before contact with the deposit also suggests an extracellular transport phenomenon. Macro-culture filtrates analyses have shown that T. helicus releases extracellular non-lipidic surface-active compounds able to lower the surface tension of culture filtrates to 49.4 mN/m. Thus, these results highlight the significance of active mechanisms to reach hydrophobic contaminants before their uptake by filamentous fungi in compartmentalized micro-environments and the potential to improve them through biostimulation approaches for soil mycoremediation.

LIMONADA: A database dedicated to the simulation of biological membranes

Cellular membranes are composed of a wide diversity of lipid species in varying proportions and these compositions are representative of the organism, cellular type and organelle to which they belong. Because models of these molecular systems simulated by MD steadily gain in size and complexity, they are increasingly representative of specific compositions and behaviors of biological membranes. Due to the number of lipid species involved, of force fields and topologies and because of the complexity of membrane objects that have been simulated, LIMONADA has been developed as an open database allowing to handle the various aspects of lipid membrane simulation. LIMONADA presents published membrane patches with their simulation files and the cellular membrane it models. Their compositions are then detailed based on the lipid identification from LIPID MAPS database plus the lipid topologies and the force field used. LIMONADA is freely accessible on the web at https://limonada.univ-reims.fr/.

The Surfactin-Like Lipopeptides From Bacillus spp.: Natural Biodiversity and Synthetic Biology for a Broader Application Range

Surfactin is a lipoheptapeptide produced by several Bacillus species and identified for the first time in 1969. At first, the biosynthesis of this remarkable biosurfactant was described in this review. The peptide moiety of the surfactin is synthesized using huge multienzymatic proteins called NonRibosomal Peptide Synthetases. This mechanism is responsible for the peptide biodiversity of the members of the surfactin family. In addition, on the fatty acid side, fifteen different isoforms (from C12 to C17) can be incorporated so increasing the number of the surfactin-like biomolecules. The review also highlights the last development in metabolic modeling and engineering and in synthetic biology to direct surfactin biosynthesis but also to generate novel derivatives. This large set of different biomolecules leads to a broad spectrum of physico-chemical properties and biological activities. The last parts of the review summarized the numerous studies related to the production processes optimization as well as the approaches developed to increase the surfactin productivity of Bacillus cells taking into account the different steps of its biosynthesis from gene transcription to surfactin degradation in the culture medium.

Truncated YY1 interacts with BASP1 through a 339KLK341 motif in YY1 and suppresses vascular smooth muscle cell growth and intimal hyperplasia after vascular injury

AIMS

In-stent restenosis and late stent thrombosis are complications associated with the use of metallic and drug-coated stents. Strategies that inhibit vascular smooth muscle cell (SMC) proliferation without affecting endothelial cell (EC) growth would be helpful in reducing complications arising from percutaneous interventions. Our group previously showed that the forced expression of the injury-inducible zinc finger (ZNF) transcription factor, yin yang-1 (YY1) comprising 414 residues inhibits neointima formation in carotid arteries of rabbits and rats. YY1 inhibits SMC proliferation without affecting EC growth. Identifying a shorter version of YY1 retaining cell-selective inhibition would make it more amenable for potential use as a gene therapeutic agent.

METHODS AND RESULTS

We dissected YY1 into a range of shorter fragments (YY1A-D, YY1Δ) and found that the first two ZNFs in YY1 (construct YY1B, spanning 52 residues) repressed SMC proliferation. Receptor Binding Domain analysis predicts a three residue (339KLK341) interaction domain. Mutation of 339KLK341 to 339AAA341 in YY1B (called YY1Bm) abrogated YY1B's ability to inhibit SMC but not EC proliferation and migration. Incubation of recombinant GST-YY1B and GST-YY1Bm with SMC lysates followed by precipitation with glutathione-agarose beads and mass spectrometric analysis identified a novel interaction between YY1B and BASP1. Overexpression of BASP1, like YY1, inhibited SMC but not EC proliferation and migration. BASP1 siRNA partially rescued SMC from growth inhibition by YY1B. In the rat carotid balloon injury model, adenoviral overexpression of YY1B, like full-length YY1, reduced neointima formation, whereas YY1Bm had no such effect. CD31 immunostaining suggested YY1B could increase re-endothelialization in a 339KLK341-dependent manner.

CONCLUSIONS

These studies identify a truncated form of YY1 (YY1B) that can interact with BASP1 and inhibits SMC proliferation, migration and intimal hyperplasia after balloon injury of rat carotid arteries as effectively as full length YY1. We demonstrate the therapeutic potential of YY1B in vascular proliferative disease.

The Trypanosoma Brucei KIFC1 Kinesin Ensures the Fast Antibody Clearance Required for Parasite Infectivity

Human innate immunity to Trypanosoma brucei involves the trypanosome C-terminal kinesin TbKIFC1, which transports internalized trypanolytic factor apolipoprotein L1 (APOL1) within the parasite. We show that TbKIFC1 preferentially associates with cholesterol-containing membranes and is indispensable for mammalian infectivity. Knockdown of TbKIFC1 did not affect trypanosome growth in vitro but rendered the parasites unable to infect mice unless antibody synthesis was compromised. Surface clearance of Variant Surface Glycoprotein (VSG)-antibody complexes was far slower in these cells, which were more susceptible to capture by macrophages. This phenotype was not due to defects in VSG expression or trafficking but to decreased VSG mobility in a less fluid, stiffer surface membrane. This change can be attributed to increased cholesterol level in the surface membrane in TbKIFC1 knockdown cells. Clearance of surface-bound antibodies by T. brucei is therefore essential for infectivity and depends on high membrane fluidity maintained by the cholesterol-trafficking activity of TbKIFC1.

Contributions and Limitations of Biophysical Approaches to Study of the Interactions between Amphiphilic Molecules and the Plant Plasma Membrane

Some amphiphilic molecules are able to interact with the lipid matrix of plant plasma membranes and trigger the immune response in plants. This original mode of perception is not yet fully understood and biophysical approaches could help to obtain molecular insights. In this review, we focus on such membrane-interacting molecules, and present biophysically grounded methods that are used and are particularly interesting in the investigation of this mode of perception. Rather than going into overly technical details, the aim of this review was to provide to readers with a plant biochemistry background a good overview of how biophysics can help to study molecular interactions between bioactive amphiphilic molecules and plant lipid membranes. In particular, we present the biomimetic membrane models typically used, solid-state nuclear magnetic resonance, molecular modeling, and fluorescence approaches, because they are especially suitable for this field of research. For each technique, we provide a brief description, a few case studies, and the inherent limitations, so non-specialists can gain a good grasp on how they could extend their toolbox and/or could apply new techniques to study amphiphilic bioactive compound and lipid interactions.

Plant-Pathogen Interactions: Underestimated Roles of Phyto-oxylipins

Plant (or phyto-) oxylipins (POs) are produced under a wide range of stress conditions and although they are well known to activate stress-related signalling pathways, the nonsignalling roles of POs are poorly understood. We describe oxylipins as direct biocidal agents and propose that structure-function relationships play here a pivotal role. Based on their chemical configuration, POs, such as reactive oxygen and electrophile species, activate defence-related gene expression. We also propose that their ability to interact with pathogen membranes is important, but still misunderstood, and that they are involved in cross-kingdom communication. Taken as a whole, the current literature suggests that POs have a high potential as biocontrol agents. However, the mechanisms underlying these multifaceted compounds remain largely unknown.

Molecular Model for the Self-Assembly of the Cyclic Lipodepsipeptide Pseudodesmin A

Self-assembly of peptides into supramolecular structures represents an active field of research with potential applications ranging from material science to medicine. Their study typically involves the application of a large toolbox of spectroscopic and imaging techniques. However, quite often, the structural aspects remain underexposed. Besides, molecular modeling of the self-assembly process is usually difficult to handle, since a vast conformational space has to be sampled. Here, we have used an approach that combines short molecular dynamics simulations for peptide dimerization and NMR restraints to build a model of the supramolecular structure from the dimeric units. Experimental NMR data notably provide crucial information about the conformation of the monomeric units, the supramolecular assembly dimensions, and the orientation of the individual peptides within the assembly. This in silico/in vitro mixed approach enables us to define accurate atomistic models of supramolecular structures of the bacterial cyclic lipodepsipeptide pseudodesmin A.

Multiple C2 domains and transmembrane region proteins (MCTPs) tether membranes at plasmodesmata

In eukaryotes, membrane contact sites (MCS) allow direct communication between organelles. Plants have evolved a unique type of MCS, inside intercellular pores, the plasmodesmata, where endoplasmic reticulum (ER)-plasma membrane (PM) contacts coincide with regulation of cell-to-cell signalling. The molecular mechanism and function of membrane tethering within plasmodesmata remain unknown. Here, we show that the multiple C2 domains and transmembrane region protein (MCTP) family, key regulators of cell-to-cell signalling in plants, act as ER-PM tethers specifically at plasmodesmata. We report that MCTPs are plasmodesmata proteins that insert into the ER via their transmembrane region while their C2 domains dock to the PM through interaction with anionic phospholipids. A Atmctp3/Atmctp4 loss of function mutant induces plant developmental defects, impaired plasmodesmata function and composition, while MCTP4 expression in a yeast Δtether mutant partially restores ER-PM tethering. Our data suggest that MCTPs are unique membrane tethers controlling both ER-PM contacts and cell-to-cell signalling.

Is It Possible to Predict the Odor of a Molecule on the Basis of its Structure?

The olfactory sense is the dominant sensory perception for many animals. When Richard Axel and Linda B. Buck received the Nobel Prize in 2004 for discovering the G protein-coupled receptors’ role in olfactory cells, they highlighted the importance of olfaction to the scientific community. Several theories have tried to explain how cells are able to distinguish such a wide variety of odorant molecules in a complex context in which enantiomers can result in completely different perceptions and structurally different molecules. Moreover, sex, age, cultural origin, and individual differences contribute to odor perception variations that complicate the picture. In this article, recent advances in olfaction theory are presented, and future trends in human olfaction such as structure-based odor prediction and artificial sniffing are discussed at the frontiers of chemistry, physiology, neurobiology, and machine learning.

The activity of the saponin ginsenoside Rh2 is enhanced by the interaction with membrane sphingomyelin but depressed by cholesterol

The membrane activity of some saponins, such as digitonin or alpha-hederin, is usually attributed to their interaction with membrane cholesterol (Chol). This contrasts with our recent publication showing that Chol, contrary to sphingomyelin (SM), can delay the cytotoxicity of the saponin ginsenoside Rh2, challenging the usual view that most saponins mediate their membrane effects through interaction with Chol. The aim of the present study was to elucidate the respective importance of Chol and SM as compared to phosphatidylcholine (PC) species in the membrane-related effects of Rh2. On simple lipid monolayers, Rh2 interacted more favorably with eggSM and DOPC than with Chol and eggPC. Using Large Unilamellar Vesicles (LUVs) of binary or ternary lipid compositions, we showed that Rh2 increased vesicle size, decreased membrane fluidity and induced membrane permeability with the following preference: eggSM:eggPC > eggSM:eggPC:Chol > eggPC:Chol. On Giant Unilamellar Vesicles (GUVs), we evidenced that Rh2 generated positive curvatures in eggSM-containing GUVs and small buds followed by intra-luminal vesicles in eggSM-free GUVs. Altogether, our data indicate that eggSM promotes and accelerates membrane-related effects induced by Rh2 whereas Chol slows down and depresses these effects. This study reconsiders the theory that Chol is the only responsible for the activity of saponins.

Lipids or Proteins: Who Is Leading the Dance at Membrane Contact Sites?

Understanding the mode of action of membrane contact sites (MCSs) across eukaryotic organisms at the near-atomic level to infer function at the cellular and tissue levels is a challenge scientists are currently facing. These peculiar systems dedicated to inter-organellar communication are perfect examples of cellular processes where the interplay between lipids and proteins is critical. In this mini review, we underline the link between membrane lipid environment, the recruitment of proteins at specialized membrane domains and the function of MCSs. More precisely, we want to give insights on the crucial role of lipids in defining the specificity of plant endoplasmic reticulum (ER)-plasma membrane (PM) MCSs and we further propose approaches to study them at multiple scales. Our goal is not so much to go into detailed description of MCSs, as there are numerous focused reviews on the subject, but rather try to pinpoint the critical elements defining those structures and give an original point of view by considering the subject from a near-atomic angle with a focus on lipids. We review current knowledge as to how lipids can define MCS territories, play a role in the recruitment and function of the MCS-associated proteins and in turn, how the lipid environment can be modified by proteins.

Homology modeling and in vivo functional characterization of the zinc permeation pathway in a heavy metal P-type ATPase

The P1B ATPase heavy metal ATPase 4 (HMA4) is responsible for zinc and cadmium translocation from roots to shoots in Arabidopsis thaliana. It couples ATP hydrolysis to cytosolic domain movements, enabling metal transport across the membrane. The detailed mechanism of metal permeation by HMA4 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 ionic interaction/hydrogen 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.

Interactions Between Natural Herbicides and Lipid Bilayers Mimicking the Plant Plasma Membrane

Natural phytotoxic compounds could become an alternative to traditional herbicides in the framework of sustainable agriculture. Nonanoic acid, sarmentine and sorgoleone are such molecules extracted from plants and able to inhibit the growth of various plant species. However, their mode of action is not fully understood and despite clues indicating that they could affect the plant plasma membrane, molecular details of such phenomenon are lacking. In this paper, we investigate the interactions between those natural herbicides and artificial bilayers mimicking the plant plasma membrane. First, their ability to affect lipid order and fluidity is evaluated by means of fluorescence measurements. It appears that sorgoleone has a clear ordering effect on lipid bilayers, while nonanoic acid and sarmentine induce no or little change to these parameters. Then, a thermodynamic characterization of interactions of each compound with lipid vesicles is obtained with isothermal titration calorimetry, and their respective affinity for bilayers is found to be ranked as follows: sorgoleone > sarmentine > nonanoic acid. Finally, molecular dynamics simulations give molecular details about the location of each compound within a lipid bilayer and confirm the rigidifying effect of sorgoleone. Data also suggest that mismatch in alkyl chain length between nonanoic acid or sarmentine and lipid hydrophobic tails could be responsible for bilayer destabilization. Results are discussed regarding their implications for the phytotoxicity of these compounds.

Insight into the Self-Assembling Properties of Peptergents: A Molecular Dynamics Simulation Study

By manipulating the various physicochemical properties of amino acids, the design of peptides with specific self-assembling properties has been emerging for 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 and extensively described by Tao et al., is studied by molecular dynamic simulations for its self-assembling properties in different conditions. In water, it spontaneously forms 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 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, which was 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".

How different sterols contribute to saponin tolerant plasma membranes in sea cucumbers

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.

Interaction between the barley allelochemical compounds gramine and hordenine and artificial lipid bilayers mimicking the plant plasma membrane

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.

Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins

Necrosis and ethylene-inducing peptide 1-like (NLP) proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. Many NLPs are cytotoxins that facilitate microbial infection of eudicot, but not of monocot plants. Here, we report glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors. Plant mutants with altered GIPC composition were more resistant to NLP toxins. Binding studies and x-ray crystallography showed that NLPs form complexes with terminal monomeric hexose moieties of GIPCs that result in conformational changes within the toxin. Insensitivity to NLP cytolysins of monocot plants may be explained by the length of the GIPC head group and the architecture of the NLP sugar-binding site. We unveil early steps in NLP cytolysin action that determine plant clade-specific toxin selectivity.

Differential Interaction of Synthetic Glycolipids with Biomimetic Plasma Membrane Lipids Correlates with the Plant Biological Response

Natural and synthetic amphiphilic molecules including lipopeptides, lipopolysaccharides, and glycolipids are able to induce defense mechanisms in plants. In the present work, the perception of two synthetic C14 rhamnolipids, namely, Alk-RL and Ac-RL, differing only at the level of the lipid tail terminal group have been investigated using biological and biophysical approaches. We showed that Alk-RL induces a stronger early signaling response in tobacco cell suspensions than does Ac-RL. The interactions of both synthetic RLs with simplified biomimetic membranes were further analyzed using experimental and in silico approaches. Our results indicate that the interactions of Alk-RL and Ac-RL with lipids were different in terms of insertion and molecular responses and were dependent on the lipid composition of model membranes. A more favorable insertion of Alk-RL than Ac-RL into lipid membranes is observed. Alk-RL forms more stable molecular assemblies than Ac-RL with phospholipids and sterols. At the molecular level, the presence of sterols tends to increase the RLs' interaction with lipid bilayers, with a fluidizing effect on the alkyl chains. Taken together, our findings suggest that the perception of these synthetic RLs at the membrane level could be related to a lipid-driven process depending on the organization of the membrane and the orientation of the RLs within the membrane and is correlated with the induction of early signaling responses in tobacco cells.

Structural basis for plant plasma membrane protein dynamics and organization into functional nanodomains

Plasma Membrane is the primary structure for adjusting to ever changing conditions. PM sub-compartmentalization in domains is thought to orchestrate signaling. Yet, mechanisms governing membrane organization are mostly uncharacterized. The plant-specific REMORINs are proteins regulating hormonal crosstalk and host invasion. REMs are the best-characterized nanodomain markers via an uncharacterized moiety called REMORIN C-terminal Anchor. By coupling biophysical methods, super-resolution microscopy and physiology, we decipher an original mechanism regulating the dynamic and organization of nanodomains. We showed that targeting of REMORIN is independent of the COP-II-dependent secretory pathway and mediated by PI4P and sterol. REM-CA is an unconventional lipid-binding motif that confers nanodomain organization. Analyses of REM-CA mutants by single particle tracking demonstrate that mobility and supramolecular organization are critical for immunity. This study provides a unique mechanistic insight into how the tight control of spatial segregation is critical in the definition of PM domain necessary to support biological function.

Atrophic Maxilla Reconstruction With Fresh Frozen Allograft Bone, Titanium Mesh, and Platelet-Rich Fibrin: Case Report

The purpose of this article was to report the clinical and radiographic findings about a case of a man affected by severely atrophic maxilla to demonstrate the clinical proceedings associated with alveolar reconstruction destined for dental implant rehabilitation. The 3-dimensional augmentation of the alveolar ridge with the use of fresh-frozen bone graft, platelet-rich fibrin membrane, and titanium mesh suggests potential benefits to the development of the bone formation physiology. The treatment combination may result in an optimal prognosis and represents an option for reconstruction of bone defects. At 8 months after surgery, no evidence of complications was observed; the clinical examination and computerized tomographic scan revealed bone formation and installed implant stability.

Negatively Charged Lipids as a Potential Target for New Amphiphilic Aminoglycoside Antibiotics: A BIOPHYSICAL STUDY

Bacterial membranes are highly organized, containing specific microdomains that facilitate distinct protein and lipid assemblies. Evidence suggests that cardiolipin molecules segregate into such microdomains, probably conferring a negative curvature to the inner plasma membrane during membrane fission upon cell division. 3',6-Dinonyl neamine is an amphiphilic aminoglycoside derivative active against Pseudomonas aeruginosa, including strains resistant to colistin. The mechanisms involved at the molecular level were identified using lipid models (large unilamellar vesicles, giant unilamelllar vesicles, and lipid monolayers) that mimic the inner membrane of P. aeruginosa The study demonstrated the interaction of 3',6-dinonyl neamine with cardiolipin and phosphatidylglycerol, two negatively charged lipids from inner bacterial membranes. This interaction induced membrane permeabilization and depolarization. Lateral segregation of cardiolipin and membrane hemifusion would be critical for explaining the effects induced on lipid membranes by amphiphilic aminoglycoside antibiotics. The findings contribute to an improved understanding of how amphiphilic aminoglycoside antibiotics that bind to negatively charged lipids like cardiolipin could be promising antibacterial compounds.

Revisiting Plant Plasma Membrane Lipids in Tobacco: A Focus on Sphingolipids

The lipid composition of plasma membrane (PM) and the corresponding detergent-insoluble membrane (DIM) fraction were analyzed with a specific focus on highly polar sphingolipids, so-called glycosyl inositol phosphorylceramides (GIPCs). Using tobacco (Nicotiana tabacum) 'Bright Yellow 2' cell suspension and leaves, evidence is provided that GIPCs represent up to 40 mol % of the PM lipids. Comparative analysis of DIMs with the PM showed an enrichment of 2-hydroxylated very-long-chain fatty acid-containing GIPCs and polyglycosylated GIPCs in the DIMs. Purified antibodies raised against these GIPCs were further used for immunogold-electron microscopy strategy, revealing the distribution of polyglycosylated GIPCs in domains of 35 ± 7 nm in the plane of the PM. Biophysical studies also showed strong interactions between GIPCs and sterols and suggested a role for very-long-chain fatty acids in the interdigitation between the two PM-composing monolayers. The ins and outs of lipid asymmetry, raft formation, and interdigitation in plant membrane biology are finally discussed.

Domain formation and permeabilization induced by the saponin α-hederin and its aglycone hederagenin in a cholesterol-containing bilayer

Saponins and triterpenic acids have been shown to be able to interact with lipid membranes and domains enriched with cholesterol (rafts). How saponins are able to modulate lipid phase separation in membranes and the role of the sugar chains for this activity is unknown. We demonstrate in a binary membrane model composed of DMPC/Chol (3:1 mol/mol) that the saponin α-hederin and its aglycone presenting no sugar chain, the triterpenic acid hederagenin, are able to induce the formation of lipid domains. We show on multilamellar vesicles (MLV), giant unilamellar vesicles (GUV), and supported planar bilayers (SPB) that the presence of sugar units on the sapogenin accelerates domain formation and increases the proportion of sterols within these domains. The domain shape is also influenced by the presence of sugars because α-hederin and hederagenin induce the formation of tubular and spherical domains, respectively. These highly curved structures should result from the induction of membrane curvature by both compounds. In addition to the formation of domains, α-hederin and hederagenin permeabilize GUV. The formation of membrane holes by α-hederin comes along with the accumulation of lipids into nonbilayer structures in SPB. This process might be responsible for the permeabilizing activity of both compounds. In LUV, permeabilization by α-hederin was sterol-dependent. The biological implications of our results and the mechanisms involved are discussed in relation to the activity of saponins and triterpenic acids on membrane rafts, cancer cells, and hemolysis.

Analysis of calcium-induced effects on the conformation of fengycin

Fengycin is a natural lipopeptide with antifungal and eliciting properties and able to inhibit the activity of phospholipase A2. A combination of CD, FT-IR, NMR and fluorescence spectroscopic techniques was applied to elucidate its conformation in a membrane-mimicking environment and to investigate the effect of calcium ions on it. We mainly observed that fengycin adopts a turn conformation. Our results showed that calcium ions are bound by the two charged glutamates. The calcium binding has an influence on the fengycin conformation and more particularly, on the environment of the tyrosine residues. The modulation of the fengycin conformation by the environmental conditions may influence its biological properties.

SAHBNET, an accessible surface-based elastic network: an application to membrane protein

Molecular Dynamics is a method of choice for membrane simulations and the rising of coarse-grained forcefields has opened the way to longer simulations with reduced calculations times. Here, we present an elastic network, SAHBNET (Surface Accessibility Hydrogen-Bonds elastic NETwork), that will maintain the structure of soluble or membrane proteins based on the hydrogen bonds present in the atomistic structure and the proximity between buried residues. This network is applied on the coarse-grained beads defined by the MARTINI model, and was designed to be more physics-based than a simple elastic network. The SAHBNET model is evaluated against atomistic simulations, and compared with ELNEDYN models. The SAHBNET is then used to simulate two membrane proteins inserted in complex lipid bilayers. These bilayers are formed by self-assembly and the use of a modified version of the GROMACS tool genbox (which is accessible through the gcgs.gembloux.ulg.ac.be website). The results show that SAHBNET keeps the structure close to the atomistic one and is successfully used for the simulation of membrane proteins.