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Biopesticides, which consist of antagonistic microorganisms, or the bioactive compounds they produce offer attractive alternatives to synthetic agrochemicals as a means of reducing plant diseases in crop production systems. In our previous study, a strain of Pseudomonas entomophila 23S was reported to have a strong antagonistic activity toward Clavibacter michiganensis subsp. michiganensis (Cmm), a pathogen of tomato bacterial canker disease, which causes serious damage to the tomato production industry. This study focused on purification and characterization of the anti-Cmm compound(s) produced by P. entomophila 23S. The cell-free supernatant was first subjected to butanol extraction, fractioned by solid-phase extraction (SPE), and purified by high-performance liquid-chromatography (HPLC). The semi-preparative purified compounds retained anti-Cmm activity. These compounds were then characterized by liquid chromatography coupled with high-resolution tandem mass spectrometry (LC-HRMS/MS) and nuclear magnetic resonance (NMR). Two anti-Cmm compounds, C15H16N2O and C16H18N2O, were isolated by this procedure. From the LC/MS spectra, the compounds were predicted to have an isoquinoline ring, the presence of which was confirmed by NMR. The compounds differed with respect to the presence of a methyl group in a side chain. In addition, P. entomophila 23S grown in different culture media produced the greatest amounts of these anti-Cmm compounds when in Nutrient Broth (NB), where bacterial growth was the slowest. NB composition is more favorable in stimulating P. entomophila 23S to produce higher amounts of these anti-Cmm compounds.

Numerous pathophysiological conditions are associated with the misfolding and aggregation of proteins into insoluble amyloid fibrils. The mechanisms by which this process leads to cellular dysfunction remain elusive, though several hypotheses point toward the perturbation of the cell plasma membrane by pre-fibrillar intermediates and/or amyloid growth. However, current models to study membrane perturbations are largely limited to synthetic lipid vesicles and most of experimental approaches cannot be transposed to complex cell-derived plasma membrane systems. Herein, vesicles originating from the plasma membrane of erythrocytes and β-pancreatic cells were used to study the perturbations induced by an amyloidogenic peptide, the islet amyloid polypeptide (IAPP). These biologically relevant lipid vesicles displayed a characteristic clustering in the presence of the amyloidogenic peptide, which was able to rupture membranes. By exploiting Förster resonance energy transfer (FRET), a rapid, simple, and potentially high-throughput assay to detect membrane perturbations of intact mammalian cell plasma membrane vesicles was implemented. The FRET kinetics of membrane perturbations closely correlated with the kinetics of thioflavin-T fluorescence associated with amyloid formation. This novel kinetics assay expands the toolbox available to study amyloid-associated membrane damage, bridging the gap between synthetic lipid vesicles and living cells.

When palladium phosphine sulfonate catalysts were used, ethylene and allyl acrylate were copolymerized. The copolymer structure was analyzed by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) and was found to contain both δ-valerolactone and γ-butyrolactones inserted within the chain. These cyclic structures were determined to be the outcome of 1,2 allyl insertions and 2,1 acrylate insertions except when the acrylate was cyclopolymerized: in this case, regiochemistry of the insertion was 1,2. This first example of cyclopolymerization with Pd phosphine sulfonate catalysts outlines the extraordinary versatility of this family of compounds and paves the way to new polyolefins containing complex repeat units built in.

International audience; Antimicrobial peptides are promising therapeutic agents to mitigate the global rise of antibiotic resistance. They generally act by perturbing the bacterial cell membrane and are thus less likely to induce resistance. Because they are membrane-active molecules, it is critical to verify and understand their potential action toward eukaryotic cells to help design effective and safe drugs. In this work, we studied the interaction of two antimicrobial peptides, aurein 1.2 and caerin 1.1, with red blood cell (RBC) membranes using in situ 31P and 2H solid-state NMR (SS-NMR). We established a protocol to integrate up to 25% of deuterated fatty acids in the membranes of ghosts, which are obtained when hemoglobin is removed from RBCs. Fatty acid incorporation and the integrity of the lipid bilayer were confirmed by SS-NMR and fluorescence confocal microscopy. Leakage assays were performed to assess the lytic power of the antimicrobial peptides. The in situ perturbation of the ghost membranes by aurein 1.2 and caerin 1.1 revealed by 31P and 2H SS-NMR is consistent with membrane perturbation through a carpet mechanism for aurein 1.2, whereas caerin 1.1 acts on RBCs via pore formation. These results are compatible with fluorescence microscopy images of the ghosts. The peptides interact with eukaryotic membranes following similar mechanisms that take place in bacteria, highlighting the importance of hydrophobicity when determining such interactions. Our work bridges model membranes and in vitro studies and provides an analytical toolbox to assess drug toxicity toward eukaryotic cells.

Photopolymerization is fundamental to many applications such as printed circuit board manufacturing, dentistry, coating, and stereolithography 3D-printing. However, the current organic cationic ini...

International audience; Microalgae are photosynthetic organisms widely distributed in nature and serve as a sustainable source of bioproducts. Their carbohydrate components are also promising candidates for bioenergy production and bioremediation, but the structural characterization of these heterogeneous polymers in cells remains a formidable problem. Here we present a widely applicable protocol for identifying and quantifying the glycan content using magic-angle-spinning (MAS) solid-state NMR (ssNMR) spectroscopy, with validation from glycosyl linkage and composition analysis deduced from mass-spectrometry (MS). Two-dimensional 13 C− 13 C correlation ssNMR spectra of a uniformly 13 C-labeled green microalga Parachlorella beijerinckii reveal that starch is the most abundant polysaccharide in a naturally cellulose-deficient strain, and this polymer adopts a well-organized and highly rigid structure in the cell. Some xyloses are present in both the mobile and rigid domains of the cell wall, with their chemical shifts partially aligned with the flat-ribbon 2-fold xylan identified in plants. Surprisingly, most other carbohydrates are largely mobile, regardless of their distribution in glycolipids or cell walls. These structural insights correlate with the high digestibility of this cellulose-deficient strain, and the in-cell ssNMR methods will facilitate the investigations of other economically important algae species.

International audience; Cell labeling is a preliminary step in multiple biophysical approaches, including the solid-state nuclear magnetic resonance (NMR) study of bacteria in vivo. Deuterium solid-state NMR has been used in the past years to probe bacterial membranes and their interactions with antimicrobial peptides, following a standard labeling protocol. Recent results from our laboratory on a slow-growing bacterium has shown the need to optimize this protocol, especially the bacterial growth time before harvest and the concentration of exogenous labeled fatty acids to be used for both Escherichia coli and Bacillus subtilis. It is also essential for the protocol to remain harmless to cells while providing optimal labeling. We have therefore developed a fast and facile approach to monitor the lipid composition of bacterial membranes under various growth conditions, combining solution 31P NMR and GCMS. Using this approach, the optimized labeling conditions of Escherichia coli and Bacillus subtilis with deuterated palmitic acid were determined. Our results show a modification of B. subtilis phospholipid profile as a function of the growth stage, as opposed to E. coli. Our protocol recommends low concentrations of exogenous palmitic acid in the growth medium, and bacteria harvest after the exponential phase.

International audience; This work investigates the potential probiotic effect of ma rennine-a natural pigme nt produ ced by the diatom Haslea ostrearia-on Vibrio splendidus. These ma rine bacteria are often considered a threat for aquacu lture; therefore, ch em ical antibiotics can be required to redu ce bacterial outbreaks. In vi vo 2 H solid-state NMR was used to probe the effects of ma rennine on the bacterial me mbrane in the exponential and stationary ph ases. Comparisons were ma de with polymyxin B (PxB)-an antibiotic used in aquacu lture and known to interact with Gram (−) bacteria me mbranes. We also investigated the effect of ma rennine using 31 P solidstate NMR on model me mbranes. Our results show that ma rennine has little effect on ph osph olipid headgroups dynamics, bu t redu ces the acyl ch ain fluidity. Our data suggest that the two antimicrobial agents perturb V. splendidus me mbranes through different me ch anism s. While PxB would alter the bacterial outer and inner me mbranes, ma rennine would act through a me mbrane stiffening me ch anism , without affecting the bilayer integrity. Our stud y proposes this microalgal pigme nt, wh ich is harm less for hu ma ns, as a potential treatme nt against vibriosis.

We report a novel and versatile method of grafting polymers onto lithium titanium oxide (LTO) by dispersion-mediated interfacial polymerization. A myriad of polymers can be grafted by this method, and the hybrid-polymer particles are compatible with all kinds of binders used in lithium-ion batteries. This method is capable of producing thin and homogenous polymer films that are useful for battery applications. A coating of poly(styrene) effectively prevents degradation of the cell after float test without affecting performance at high C rates.

The compound &ldquo, marennine&rdquo, is a blue&ndash, green pigment produced by the benthic microalgae Haslea ostrearia, with pathogenicity reduction activities against some bacteria and promising potential as a natural pigment in seafood industries. After decades of research, the chemical family of this compound still remains unclear, mainly because structural studies were impaired by the presence of co-extracted compounds in marennine isolates. To improve the purity of marennine extract, we developed a novel extraction method using a graphitic stationary phase, which provides various advantages over the previous procedure using tandem ultrafiltration. Our method is faster, more versatile, provides a better crude yield (66%, compared to 57% for ultrafiltration) and is amenable to upscaling with continuous photobioreactor cultivation. Our goal was to take advantage of the modulable surface properties of the graphitic matrix by optimizing its interactions with marennine. As such, the effects of organic modifiers, pH and reducing agents were studied. With this improvement on marennine purification, we achieved altogether the isolation of a fucoidan-related, sulfated polysaccharide from blue water. Characterization of the polysaccharides fraction suggests that roughly half of UV-absorbing compounds could be isolated from the marennine crude extracts. The identification of sulfated polysaccharides could be a major breakthrough for marennine purification, providing targeted isolation techniques. Likewise, the added value of Haslea ostrearia and the role of polysaccharides in previous marennine chemical characterization and bioactivity studies remain to be determined.

International audience; Microalgae are ubiquitous primary organisms that play key roles in the aquatic environment where they are the basis of the food web. These microorganisms also produce a variety of molecules with high added value, which find applications in human and animal nutrition, as therapeutic agents and as biofuels. Lipid membranes abound in microalgae where they protect the cell and are essential building blocks of organelles such as the chloroplast. To better understand the architecture and dynamics of microalgal cell membranes and their constituents, it is important that they are investigated in their natural environment. Solid-state nuclear magnetic resonance (SS-NMR) is emerging as a powerful tool to tackle these complex assemblies in situ on cell extracts and also in whole cells. Several nuclei can be studied to probe algal membranes and, moreover, microalgae can be fully 13 C-or 15 N-labeled in a cost-effective manner. In the case of full organism labelling, the challenge of SS-NMR is to develop and identify experiments to filter specific constituent signals. In this chapter, we show how SS-NMR can provide a wealth of information on the structure, dynamics and composition of microalgal membranes. We also summarize the main SS-NMR approaches so far applied on lipid extracts or whole cells under near to native conditions and suggest potential avenues to improve our understanding of these systems.

Protein misfolding and amyloid deposition are associated with numerous diseases. The detailed characterization of the proteospecies mediating cell death remains elusive owing to the (supra)structural polymorphism and transient nature of the assemblies populating the amyloid pathway. Here we describe the identification of toxic amyloid fibrils with oligomer-like characteristics, which were assembled from an islet amyloid polypeptide (IAPP) derivative containing an Asn-to-Gln substitution (N21Q). While N21Q filaments share structural properties with cytocompatible fibrils, including the 4.7 Å inter-strand distance and β-sheet-rich conformation, they concurrently display characteristics of oligomers, such as low thioflavin-T binding, high surface hydrophobicity and recognition by the A11 antibody, leading to high potency to disrupt membranes and cause cellular dysfunction. The toxic oligomer-like conformation of N21Q fibrils, which is preserved upon elongation, is transmissible to naïve IAPP. These stable fibrils expanding the conformational diversity of amyloid assemblies represent an opportunity to elucidate the structural basis of amyloid disorders., Nguyen et al identified cytotoxic amyloid fibrils with oligomer-like characteristics, which were assembled from an islet amyloid polypeptide (IAPP) derivative containing an Asn-to-Gln substitution (N21Q). They presented evidence to show that these stable fibrils expand the conformational diversity of amyloid assemblies, which represents an opportunity to elucidate the structural basis of amyloid disorders.

International audience; We present a new membrane mimetic system using a membrane softening detergent commonly known as Tween 80 (TW80), to form oriented systems for solid-state NMR applications. TW80 is a fatty acid ester (oleate) of sorbitan polyethoxylate and a mild non-ionic surfactant. Phosphatidylcholine (PC)/TW80 model membrane systems were characterized by solid-state NMR and FTIR spectroscopy. 31 P and 2 H NMR spectra showed that DMPC (14:0) and DPPC (16:0) self-assemble with TW80 to form oriented structures, and maintain alignment over a wide range of molar ratios and temperatures. The addition of lanthanide ions revealed that the membrane alignment can be flipped from parallel to perpendicular with respect to the magnetic field direction. Using 15 N solid-state NMR and a labeled model transmembrane peptide, we showed that TW80-based membranes can be employed to determine the peptide orientation in the magnetic field, which is useful for structural determination. Altogether, our work showed that TW80 could be exploited for direct and efficient membrane protein extraction and to enhance membrane and membrane protein orientation without using a detergent removal step. This approach could be extended to a wide range of membranes including native ones.

In vivo or whole-cell solid-state NMR is an emerging field which faces tremendous challenges. In most cases, cell biochemistry does not allow the labelling of specific molecules and an in vivo study is thus hindered by the inherent difficulty of identifying, among a formidable number of resonances, those arising from a given molecule. In this work we examined the possibility of studying, by solid-state NMR, the model organism Chlamydomonas reinhardtii fully and non-specifically 13C labelled. The extension of NMR-based dynamic filtering from one-dimensional to two-dimensional experiments enabled an enhanced selectivity which facilitated the assignment of cell constituents. The number of resonances detected with these robust and broadly applicable experiments appears to be surprisingly sparse. Various constituents, notably galactolipids abundant in organelle membranes, carbohydrates from the cell wall, and starch from storage grains could be unambiguously assigned. Moreover, the dominant crystal form of starch could be determined in situ. This work illustrates the feasibility and caveats of using solid-state NMR to study intact non-specifically 13C labelled micro-organisms.

Silver nanoparticles (AgNPs) are incorporated in many consumer products and have a high-releasing potential in aquatic environments. In these environments, AgNPs could interact with colloidal natural organic matter (NOM) affecting their behavior and fate. Aggregation kinetics of AgNPs were conducted at 10 NaCl concentrations during 2 h with 2.5 or 25 mgNOM L−1. Four (4) colloidal NOM fractions were extracted from 50 m3 of St.-Lawrence estuarine waters: fulvic acids (SLFA), humic acids (SLHA), hydrophilic (SL4ILE), and hydrophobic (SL4OBE) fractions. The addition of NOM to AgNP dispersion in nanopure water induced a small increase in AgNP size depending on NOM concentration and fraction used. The presence of both salt and NOM significantly altered the size of silver aggregates. With added 2.5 mgNOM L−1, more than 90% of particles have a size smaller than 200 nm, independently of the NOM fraction used. At 25 mgNOM L−1, the particle size distribution was strongly affected by the nature of NOM fractions. Our results show that NOM with highly aromatic carbon content such as SLFA and SLHA promoted the formation of larger aggregates with a hydrodynamic diameter larger than 200 nm. A high content in non-polar aliphatic carbon as observed in SL4ILE and SL4OBE stabilized aggregates at a size below 200 nm. This study highlights the importance of the chemical composition of NOM fractions and their content in non-polar aliphatic and aromatic carbons as they are involved in hydrophobic effects and strongly influence the aggregate size distribution. Sulfur, also present at low concentration NOM fractions, appears to be involved in the aggregation of AgNPs, but its action mechanism was not determined.

Owing to the presence of abundant interchain interactions such as hydrogen bonds, polyureas (PU) are only swellable or soluble in a limited number of highly protonic solvents, and the viscosity of the solutions obtained is very high, making their chemical structure characterization hard or even impossible by standard NMR. Accurate structure analysis is also hard by solid-state NMR due to low spectral resolution. The presence of a side reaction in their synthesis generating biuret cross-links is often invoked to explain their insolubility. Here we demonstrate that High Resolution Magic Angle Spinning (HR-MAS) NMR is an efficient tool for the chemical structure analysis even for cross-linked PU. With 1H, 13C, and 1H–15N HSQC combined, a variety of linear and cross-linked PU is analyzed by HR-MAS NMR, and conclusive information on their chemical structure is obtained, which reveals for the first time that the biuret group is absent in all PU.

Nuclear magnetic resonance (NMR) is commonly used to probe the effect of antimicrobial agents on bacterial membranes using model membrane systems. Ideally, considering the complexity of membranes, the interaction of molecules with membranes should be studied in vivo. The interactions of two antimicrobial peptides (AMPs) with intact Escherichia coli and Bacillus subtilis were investigated using deuterium solid-state NMR. Specifically, we studied caerin 1.1 and aurein 1.2 isolated from the skin of Australian tree frogs. The minimal inhibitory concentration value for E. coli and B. subtilis was about 100 μg/mL and 30 μg/mL, respectively, for both peptides. A protocol to deuterate the membrane phospholipids of non-mutated B. subtilis was established using deuterated palmitic acid. 2H NMR spectra combined with spectral moment analysis support the interaction of the two AMPs with the hydrophobic core of the bacterial membranes. The presence of peptides decreased the order of the lipid acyl chains for both E. coli and B. subtilis, but at higher peptide concentrations for the Gram(+) bacteria. This may be explained by the presence of other cell wall components, such as the negatively-charged teichoic and lipoteichoic acids in the peptidoglycan, which would interact with the AMPs and decrease their actual concentration on the membrane surface. The mechanism of action of the AMPs thus depends on their local concentration as well as the membrane environment. The differences between the AMPs interaction with E. coli and B. subtilis reveal the importance of studying intact bacteria.

International audience; Vibrio splendidus is a marine bacterium often considered as a threat in aquaculture hatcheries where it is responsible for mass mortality events, notably of bivalves' larvae. This bacterium is highly adapted to dynamic salty ecosystems where it has become an opportunistic and resistant species. To characterize their membranes as a first and necessary step toward studying bacterial interactions with diverse molecules, we established a labelling protocol for in vivo 2 H solid-state nuclear magnetic resonance (SS-NMR) analysis of V. splendidus. 2 H SS-NMR is a useful tool to study the organization and dynamics of phospholipids at the molecular level, and its application to intact bacteria is further advantageous as it allows probing acyl chains in their natural environment and study membrane interactions. In this study, we showed that V. splendidus can be labelled using deuterated palmitic acid, and demonstrated the importance of surfactant choice in the labelling protocol. Moreover, we assessed the impact of lipid deuteration on the general fitness of the bacteria, as well as the saturated-to-unsaturated fatty acid chains ratio and its impact on the membrane properties. We further characterize the evolution of V. splendidus membrane fluidity during different growth stages and relate it to fatty acid chain composition. Our results show larger membrane fluidity during the stationary growth phase compared to the exponential growth phase under labelling conditions-an information to take into account for future in vivo SS-NMR studies. Our lipid deuteration protocol optimized for V. splendidus is likely applicable other microorganisms for in vivo NMR studies.

We develop an approach for quantifying cure that applies thermodynamic modelling to interpret DSC data that is consistent with solid state NMR. The effect of elements of monomer geometry, such as the angle between functional groups and the distance between them, on curing of epoxy-amine thermosets is explored experimentally using this new technique. The effect of the angle between functional groups on the glass transition temperature of the final cured network is significant. The effect of spacing between functional groups is masked by the rigidity of the spacer. Our approach to interpreting DSC data allows us to detect processes that would have been missed otherwise. This is exemplified by the observation of slow exothermic deterioration reaction. Our NMR results indicate that significant etherification occurs at 140 °C, unlike the commonly held belief that it is insignificant at such low temperatures.

International audience

Vibrio splendidus is a marine bacterium often considered as a threat in aquaculture hatcheries where it is responsible for mass mortality events, notably of bivalves' larvae. This bacterium is highly adapted to dynamic salty ecosystems where it has become an opportunistic and resistant species. To characterize their membranes as a first and necessary step toward studying bacterial interactions with diverse molecules, we established a labelling protocol for in vivo

We report the sequential construction of a set of multivalent structures using cyclotriphosphazene (CTP) units, which were extensively used as primary or secondary cores implementing branching. The utilization of classical convergent and divergent approaches, together with accelerated dendritic strategies comprising orthogonal sequences, double-exponential and double-stage methodologies will be documented and discussed. Straightforward generation of non-conventional glycodendritic systems with surfaces rich in selectable headgroups, despite a low number of dendrimer generation, was achieved with the efficient assembly of highly functionalized AB3 and AB5 nanosynthons. The versatility of the methodology allowed access to a wide variety of structurally diversified platforms. The synthesis was completed by peripheral functionalization with spacered saccharides. The resulting architectures can be drawn as classical globular topologies, also dumbbell shapes and “onion peel” design, referred to as hypercores, wedged hypermonomers, glycoclusters, and glycodendrimers. The convenient implementation of controlled topological diversification is considered instrumental for providing sensitive and potent tools to delineate rules for structure–activity relationships in carbohydrate–protein (lectin) interactions, with possibility to tailor size, valency, ligand density, and topology. To illustrate the applicability of this approach for construction of biologically active glycoconjugates, competitive surface plasmon resonance studies were performed with a bacterial virulence factor and a human adhesion/growth-regulatory lectin and showed multivalent effects.

Microalgae are unicellular organisms in which plasma membrane is protected by a complex cell wall. The chemical nature of this barrier is important not only for taxonomic identification, but also for interactions with exogenous molecules such as contaminants. In this work, we have studied freshwater (Chlamydomonas reinhardtii) and marine (Pavlova lutheri and Nannochloropsis oculata) microalgae with different cell wall characteristics. C. reinhardtii is covered by a network of fibrils and glycoproteins, while P. lutheri is protected by small cellulose scales, and the picoplankton N. oculata by a rigid cellulose wall. The objective of this work was to determine to what extent the different components of these microorganisms (proteins, carbohydrates, lipids) can be distinguished by 13C solid-state NMR with an emphasis on isolating the signature of their cell walls and membrane lipid constituents. By using NMR experiments which select rigid or mobile zones, as well as 13C-enriched microalgal cells, we improved the spectral resolution and simplified the highly crowded spectra. Interspecies differences in cell wall constituents, storage sugars and membrane lipid compositions were thus evidenced. Carbohydrates from the cell walls could be distinguished from those incorporated into sugar reserves or glycolipids. Lipids from the plasmalemma and organelle membranes and from storage vacuoles could also be identified. This work establishes a basis for a complete characterization of phytoplankton cells by solid-state NMR.This article is part of a Special Issue entitled: NMR Spectroscopy for Atomistic Views of Biomembranes and Cell Surfaces. Guest Editors: Lynette Cegelski and David P. Weliky.

A variety of lipids that differ by their chains and headgroups are found in biomembranes. In addition to studying the overall membrane phase, determination of the structure, dynamics, and headgroup conformation of individual lipids in the mixture would be of great interest. We have thus developed, to our knowledge, a new approach using solid-state (31)P NMR, magic-angle spinning, and chemical-shift anisotropy (CSA) recoupling, using an altered version of the recoupling of chemical shift anisotropy (ROCSA) pulse sequence, here penned PROCSA. The resulting two-dimensional spectra allowed the simultaneous measurement of the isotropic chemical shift and CSA of each lipid headgroup, thus providing a valuable measure of its dynamics and structure. PROCSA was applied to mixtures of phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) in various relative proportions, to mimic bacterial membranes and assess the respective roles of lipids in shaping these bilayers. The results were interpreted in terms of membrane topology, lipid propensity to adopt various phases or conformations, and lipid-lipid miscibility. Our results showed that PG dictates the lipid behavior when present in a proportion of 20 mol % or more. A small proportion of PG is thus able to impose a bilayer structure to the hexagonal phase forming PE. We discuss the requirement for lipids, such as PE, to be able to adopt non-bilayer phases in a membrane.

The hERG channel is a voltage-gated potassium channel found in cardiomyocytes that contributes to the repolarization of the cell membrane following the cardiac action potential, an important step in the regulation of the cardiac cycle. The lipids surrounding K+ channels have been shown to play a key role in their regulation, with anionic lipids shown to alter gating properties. In this study, we investigate how anionic lipids interact with the pore helix of hERG and compare the results with those from Kv1.5, which possesses a pore helix more typical of K+ channels. Circular dichroism studies of the pore helix secondary structure reveal that the presence of the anionic lipid DMPS within the bilayer results in a slight unfolding of the pore helices from both hERG and Kv1.5, albeit to a lesser extent for Kv1.5. In the presence of anionic lipids, the two pore helices exhibit significantly different interactions with the lipid bilayer. We demonstrate that the pore helix from hERG causes significant perturbation to the order in lipid bicelles, which contrasts with only small changes observed for Kv1.5. These observations suggest that the atypical sequence of the pore helix of hERG may play a key role in determining how anionic lipids influence its gating.

This paper describes the synthesis of three closely related families of mannopyranoside-containing dendrimers for the purpose of studying subtle structural parameters involved in the measurements of multivalent carbohydrate–protein binding interactions. Toward this goal, two trimers 5 and 9, three 9-mers 12, 17, 21, and one 27-mer 23, varying by the number of atoms separating the anomeric and the core carbons, were synthesized using azide–alkyne cycloaddition (CuAAc). Compound 23 was prepared by an efficient convergent strategy. The sugar precursors consisted of either a 2-azidoethyl (3) or a prop-2-ynyl α-D-mannopyranoside (7) derivative. The solvodynamic diameters of 9-mer 12, 17, and 21 were determined by pulsed-field-gradient-stimulated echo (PFG-STE) NMR experiments and were found to be 3.0, 2.5, and 3.4 nm, respectively.

The exceptional upconverting properties of lanthanide-doped nanoparticles make them attractive systems with applications ranging from photovoltaics to biological labeling, imaging, and therapeutics. While they draw considerable interest, structural data, which are necessary to understand the upconversion process, remain scarce. In this work, we demonstrate the use of 23Na, 19F, and 89Y solid-state NMR together with DFT calculations to characterize the structure of cubic NaYF4 nanoparticles with and without Er3+ doping. By measuring 23Na MAS NMR spectra at various magnetic fields and 3QMAS spectra at ultrahigh field, we show that the spectra are characteristic of a solid solution in which cation sites are statistically occupied by Na+ or Y3+ ions. The 23Na NMR spectra are broadened as a result of isotropic chemical shift distribution, whereas the extracted quadrupolar products appear to be small (≤1.8 MHz), which is in good agreement with DFT calculations using CASTEP. The chemical shift distribution in 19...

The crystallinity of a linear copolymer of ethylene and diacetone acrylamide (DAAM) prepared by Pd catalyzed polymerization was eliminated when reacted with hydrazine in the gas phase and recovered when treated with ozone gas.

Bicelles (bilayered micelles) are model membranes used in the study of peptide structure and membrane interactions. They are traditionally made of long- and short-chain phospholipids, usually dimyristoylphosphatidylcholine (D14PC) and dihexanoyl-PC (D6PC). They are attractive membrane mimetics because their composition and planar surface are similar to the native membrane environment. In this work, to improve the solubilization of membrane proteins and allow their study in bicellar systems, D6PC was replaced by detergents from the monoalkylphosphocholine (MAPCHO) family, of which dodecylphosphocholine (12PC) is known for its ability to solubilize membrane proteins. More specifically 12PC, tetradecyl- (14PC), and hexadecyl-PC (16PC) have been employed. To verify the possibility of making bicelles with different hydrophobic thicknesses to better accommodate membrane proteins, D14PC was also replaced by phospholipids with different alkyl chain lengths: dilauroyl-PC (D12PC), dipalmitoyl-PC (D16PC), distearoyl-PC (D18PC), and diarachidoyl-PC (D20PC). Results obtained by 31P solid-state nuclear magnetic resonance (NMR) and isothermal titration calorimetry (ITC) at several lipid-to-detergent molar ratios (q) and temperatures indicate that these new MAPCHO bicelles can be formed under a variety of conditions. The quality of their alignment is similar to that of classical bicelles, and the low critical micelle concentration (CMC) of the surfactants and their miscibility with phospholipids are likely to be advantageous for the reconstitution of membrane proteins.

Slow deactivation of Kv11.1 channels is critical for its function in the heart. The S4-S5 linker, which joins the voltage sensor and pore domains, plays a critical role in this slow deactivation gating. Here, we use NMR spectroscopy to identify the membrane-bound surface of the S4S5 linker, and we show that two highly conserved tyrosine residues within the KCNH subfamily of channels are membrane-associated. Site-directed mutagenesis and electrophysiological analysis indicates that Tyr-542 interacts with both the pore domain and voltage sensor residues to stabilize activated conformations of the channel, whereas Tyr-545 contributes to the slow kinetics of deactivation by primarily stabilizing the transition state between the activated and closed states. Thus, the two tyrosine residues in the Kv11.1 S4S5 linker play critical but distinct roles in the slow deactivation phenotype, which is a hallmark of Kv11.1 channels.

Native fullerene is notoriously insoluble in water and forms aggregates toxic to cell membranes, thus limiting its use in nanomedicine. In contrast, water-soluble fullerenol is compatible with biological systems and shows low in vivo toxicity on human cell lines. The interaction mechanism between these hydrophilic nanoparticles and biological membranes is however not well understood. Therefore, in this work, the effect of fullerenol on model eukaryotic and bacterial membranes was investigated using (31)P- and (2)H solid-state NMR as well as FTIR spectroscopy. DPPC/cholesterol and DPPC/DPPG bilayers were used to mimic eukaryotic and bacterial cell membranes, respectively. Our results show low affinity of fullerenol for DPPC/cholesterol bilayers but a clear interaction with model bacterial membranes. A preferential affinity of fullerenol for the anionic phospholipids DPPG in DPPC/DPPG membranes is also observed. Our data suggest that fullerenol remains at the water/bilayer interface of eukaryote-like membranes. They also indicate that the presence of a polar group such as DPPG's hydroxyl moiety at the bilayer surface plays a key role in the interaction of fullerenol with membranes. Hydrogen bonding of fullerenol nanoparticles with DPPGs' OH groups is most likely responsible for inducing lipid segregation in the lipid bilayer. Moreover, the location of the nanoparticles in the polar region of DPPG-rich regions appears to disturb the acyl chain packing and increase the membrane fluidity. The preferential interaction of fullerenol with lipids mostly found in bacterial membranes is of great interest for the design of new antibiotics.

Biological molecular processes are often studied in model systems, which simplifies their inherent complexity but may cause investigators to lose sight of the effects of the molecular environment. Information obtained in this way must therefore be validated by experiments in the cell. NMR has been used to study biological cells since the early days of its development. The first NMR structural studies of a protein inside a cell (by solution-state NMR) and of a membrane protein (by solid-state NMR) were published in 2001 and 2011, respectively. More recently, dynamic nuclear polarization, which has been used to enhance the signal in solid-state NMR, has also been applied to the study of frozen cells. Much progress has been made in the past 5 years, and in this review we take stock of this new technique, which is particularly appropriate for the study of biological membranes.

The human ether-à-go-go related gene (hERG) potassium channels are located in the myocardium cell membrane where they ensure normal cardiac activity. The binding of drugs to this channel, a side effect known as drug-induced (acquired) long QT syndrome (ALQTS), can lead to arrhythmia or sudden cardiac death. The hERG channel is a unique member of the family of voltage-gated K+ channels because of the long extracellular loop connecting its transmembrane S5 helix to the pore helix in the pore domain. Considering the proximal position of the S5-P linker to the membrane surface, we have investigated the interaction of its central segment I(583)-Y(597) with bicelles. Liquid and solid-state NMR experiments as well as circular dichroism results show a strong affinity of the I(583)-Y(597) segment for the membrane where it would sit on the surface with no defined secondary structure. A structural dependence of this segment on model membrane composition was observed. A helical conformation is favoured in detergent micelles and in the presence of negative charges. Our results suggest that the interaction of the S5-P linker with the membrane could participate in the stabilization of transient channel conformations, but helix formation would be triggered by interactions with other hERG domains. Because potential drug binding sites on the S5-P linker have been identified, we have explored the role of this segment in ALQTS. Four LQTS-liable drugs were studied which showed more affinity for the membrane than this hERG segment. Our results, therefore, identify two possible roles for the membrane in channel functioning and ALQTS.

As a consequence of evolutionary pressure, various organisms have developed structural fibers displaying a range of exceptional mechanical properties adapted specifically to their functions. An understanding of these properties at the molecular level requires a detailed description of local structure, orientation with respect to the fiber and size of constitutive units, and dynamics on various timescales. The size and lack of long-range order in these protein systems constitute an important challenge to classical structural techniques such as high-resolution NMR and X-ray diffraction. Solid-state NMR overcomes these constraints and is uniquely suited to the study of these inherently disordered systems. Solid-state NMR experiments developed or applied to determine structure, orientation, and dynamics of these complex proteins will be reviewed and illustrated through examples of their applications to fibers such as spider and silkworm silks, collagen, elastin, and keratin. © 2009 Wiley Periodicals, Inc. Concepts Magn Reson Part A 34A: 24–27, 2009.

Short-rotation intensive cultures (SRICs) of willows can potentially sequester carbon (C) in soil. However, there is limited information regarding the factors governing soil organic C (Corg) accumulation following afforestation. The objectives of this study were to: (i) determine whether willow leads to Corg accumulation in the topsoil (0–10 cm) two to six years after establishment in five SRICs located along a large climatic/productivity gradient in southern Quebec, and (ii) assess the influence of leaf litter decomposition and soil organic matter (OM) quality on Corg accumulation in the topsoil. Topsoil Corg concentrations and pools under SRICs were, on average, 25% greater than reference fields, and alkyls concentrations were higher under SRICs. On an annualized basis, Corg accumulation rates in the topsoil varied between 0.4 and 4.5 Mg ha−1 yr−1. Estimated annual litterfall C fluxes were in the same order of magnitude, suggesting that SRICs can accumulate Corg in the topsoil during early years due to high growth rates. Leaf litter decomposition was also related to Corg accumulation rates in the topsoil. It was positively correlated to growing season length, degree-days, and growing season average air and topsoil temperature (r &gt, 0.70), and negatively correlated to topsoil volumetric water content (r = −0.55). Leaf litter decomposition likely occurred more quickly than that of plants in reference fields, and as it progressed, OM became more decay resistant, more stable and accumulated as Corg in the topsoil.

We report the observation of undetected (until now) residues of the prion protein fragment HET-s(218-289) which give rise to well-resolved (13)C, (15)N, and (1)H NMR resonances under high-resolution magic-angle spinning (HRMAS) conditions. The observed signals belong to large polymeric units as shown by measuring the lateral diffusion constants. The amino acids identified in the spectra are compatible with their localization in the segments of the protein which could not be detected in earlier solid-state NMR experiments. The observed chemical shifts indicate that these residues are in a random-coil conformation. Complementary experiments which detect only dynamic or static residues, respectively, strongly suggest that they belong to different parts of the same molecule.

The influence of salts (KCl, NaCl, CaCl(2), and MgCl(2)) on bicelles (bilayered micelles) made of dimyristoylphosphatidylcholine (DMPC, molar fraction X = 78%) and dicaproylphosphatidylcholine (DCPC) was investigated by solid-state (31)P- and (2)H NMR as well as by freeze-fracture electron microscopy. Sizes were determined from (2)H- and (31)P NMR on the basis of a model that incorporated a planar bilayer and a (half-torus) curved rim representing the DMPC and DCPC regions of the bicelle, respectively. Good agreement was shown with sizes determined independently from freeze-fracture electron microscopy images. In the presence of K(+) and Na(+), bicelles have diameters of approximately 300 A while in the presence of Ca(2+) and Mg(2+); their diameter increases to approximately 500 A. Bicelle magnetic alignment is considerably improved by the presence of salts. The optimum salt concentration for such an effect ranges from 50 to 200 mM. Bicelles are magnetically aligned for temperatures roughly ranging from 30 degrees C to 40 degrees C with monovalent cations; this range is slightly extended in the presence of divalent salts. In this temperature range, the dynamics of the long-chain hydrocarbon region of the bicelle (leading to a bicelle thickness of 38 A) and of water is about the same independently of cation nature and concentration. However, at higher temperatures, considerable differences in water dynamics are observed between systems with monovalent and divalent cations. In these conditions, the system consists of a mixture of micelles and extended bilayers, which show residual macroscopic alignment in the magnetic field.

Antimicrobial peptides (AMPs) are promising candidates to act against drug-resistant bacteria since they can disrupt the bacterial lipid barrier, leading to cell death. 2H solid-state NMR is a valuable tool to study at a molecular level the action of AMPs on the lipid organization and dynamics within the membrane bilayer. While these studies are usually performed with model phospholipid membranes, the complexity of the bacterial cell wall prompts the development of in-cell NMR techniques to take into account interactions of all constituents. In particular, Gram(−) bacteria are protected by lipopolysaccharides in their outer membrane while a thick peptidoglycan covers the lipid bilayer of Gram(+) bacteria. We have thus developed novel 2H solid-state NMR tools to study in vivo the bactericidal action mechanism of aurein 1.2 and caerin 1.1, AMPs excreted by frog skin. Using deuterated palmitic acid, we have established a protocol to 2H-label phospholipids in Gram(+) Bacillus subtilis, and optimized the deuteration protocol of Gram(−) Escherichia coli. Via a combination of static and magic-angle spinning (MAS) experiments, our results support the interaction of the AMPs with membrane lipids leading to decrease in lipid chain order. This effect is, however, observed at higher peptide concentration with B. subtilis and most likely attributable to an interaction with negatively-charged components in its cell walls, such as teichoic acids. Our study shows that the nature of the cell wall plays a role upon the actual concentration of AMPs on the bacterial membrane and highlights the importance of studying membrane interactions with intact bacteria.

Bicelles are model membranes generally made of long-chain dimyristoylphosphatidylcholine (DMPC) and short-chain dihexanoyl-PC (DHPC). They are extensively used in the study of membrane interactions and structure determination of membrane-associated peptides, since their composition and morphology mimic the widespread PC-rich natural eukaryotic membranes. At low DMPC/DHPC (q) molar ratios, fast-tumbling bicelles are formed in which the DMPC bilayer is stabilized by DHPC molecules in the high-curvature rim region. Experimental constraints imposed by techniques such as circular dichroism, dynamic light scattering, or microscopy may require the use of bicelles at high dilutions. Studies have shown that such conditions induce the formation of small aggregates and alter the lipid-to-detergent ratio of the bicelle assemblies. The objectives of this work were to determine the exact composition of those DMPC/DHPC isotropic bicelles and study the lipid miscibility. This was done using 31P nuclear magnetic resonance (NMR) and exploring a wide range of lipid concentrations (2–400 mM) and q ratios (0.15–2). Our data demonstrate how dilution modifies the actual DMPC/DHPC molar ratio in the bicelles. Care must be taken for samples with a total lipid concentration ≤250 mM and especially at q ∼ 1.5–2, since moderate dilutions could lead to the formation of large and slow-tumbling lipid structures that could hinder the use of solution NMR methods, circular dichroism or dynamic light scattering studies. Our results, supported by infrared spectroscopy and molecular dynamics simulations, also show that phospholipids in bicelles are largely segregated only when q > 1. Boundaries are presented within which control of the bicelles’ q ratio is possible. This work, thus, intends to guide the choice of q ratio and total phospholipid concentration when using isotropic bicelles.