Effects of calcium-induced aggregation on the physical stability of liposomes containing plant glycolipids

Comprehensive analysis of physiological and metabolomic responses to drought reveals specific modulation of acquired tolerance mechanisms in rice

Mild stresses induce "acquired tolerance traits" (ATTs) that provide tolerance when stress becomes severe. Here, we identified the genetic variability in ATTs among a panel of rice germplasm accessions and demonstrated their relevance in protecting growth and productivity under water-limited conditions. Diverse approaches, including physiological screens, association mapping and metabolomics, were adopted and revealed 43 significant marker-trait associations. Nontargeted metabolomic profiling of contrasting genotypes revealed 26 "tolerance-related-induced" primary and secondary metabolites in the tolerant genotypes (AC-39000 and AC-39020) compared to the susceptible one (BPT-5204) under water-limited condition. Metabolites that help maintain cellular functions, especially Calvin cycle processes, significantly accumulated more in tolerant genotypes, which resulted in superior photosynthetic capacity and hence water use efficiency. Upregulation of the glutathione cycle intermediates explains the ROS homeostasis among the tolerant genotypes, maintaining spikelet fertility, and grain yield under stress. Bioinformatic dissection of a major effect quantitative trait locus on chromosome 8 revealed genes controlling metabolic pathways leading to the production of osmolites and antioxidants, such as GABA and raffinose. The study also led to the identification of specific trait donor genotypes that can be effectively used in translational crop improvement activities.

Development of Vancomycin Delivery Systems Based on Autologous 3D Platelet-Rich Fibrin Matrices for Bone Tissue Engineering

Autologous platelet-rich fibrin (PRF) is derived from the blood and its use in the bone tissue engineering has emerged as an effective strategy for novel drug and growth factor delivery systems. Studies have approved that combined therapy with PRF ensures higher biological outcomes, but patients still undergo additional treatment with antibiotic drugs before, during, and even after the implantation of biomaterials with PRF. These systematically used drugs spread throughout the blood and lead not only to positive effects but may also induce adverse side effects on healthy tissues. Vancomycin hydrochloride (VANKA) is used to treat severe Staphylococcal infections but its absorption in the target tissue after oral administration is low; therefore, in this study, we have developed and analyzed two kinds of VANKA carriers—liposomes and microparticles in 3D PRF matrices. The adjustment, characterization, and analysis of VANKA carriers in 3D PRF scaffolds is carried out in terms of encapsulation efficiency, drug release kinetics and antibacterial activity; furthermore, we have studied the micro- and macrostructure of the scaffolds with microtomography.

Conserved Glycines Control Disorder and Function in the Cold-Regulated Protein, COR15A

Cold-regulated (COR) 15A is an intrinsically disordered protein (IDP) from Arabidopsis thaliana important for freezing tolerance. During freezing-induced cellular dehydration, COR15A transitions from a disordered to mostly α-helical structure. We tested whether mutations that increase the helicity of COR15A also increase its protective function. Conserved glycine residues were identified and mutated to alanine. Nuclear magnetic resonance (NMR) spectroscopy was used to identify residue-specific changes in helicity for wildtype (WT) COR15A and the mutants. Circular dichroism (CD) spectroscopy was used to monitor the coil–helix transition in response to increasing concentrations of trifluoroethanol (TFE) and ethylene glycol. The impact of the COR15A mutants on the stability of model membranes during a freeze–thaw cycle was investigated by fluorescence spectroscopy. The results of these experiments showed the mutants had a higher content of α-helical structure and the increased α-helicity improved membrane stabilization during freezing. Comparison of the TFE- and ethylene glycol-induced coil–helix transitions support our conclusion that increasing the transient helicity of COR15A in aqueous solution increases its ability to stabilize membranes during freezing. Altogether, our results suggest the conserved glycine residues are important for maintaining the disordered structure of COR15A but are also compatible with the formation of α-helical structure during freezing induced dehydration.

Rice intermediate filament, OsIF, stabilizes photosynthetic machinery and yield under salinity and heat stress

Cytoskeleton plays a vital role in stress tolerance; however, involvement of intermediate filaments (IFs) in such a response remains elusive in crop plants. This study provides clear evidence about the unique involvement of IFs in cellular protection against abiotic stress in rice. Transcript abundance of Oryza sativa intermediate filament (OsIF) encoding gene showed 2-10 fold up-regulation under different abiotic stress. Overexpression of OsIF in transgenic rice enhanced tolerance to salinity and heat stress, while its knock-down (KD) rendered plants more sensitive thereby indicating the role of IFs in promoting survival under stress. Seeds of OsIF overexpression rice germinated normally in the presence of high salt, showed better growth, maintained chloroplast ultrastructure and favourable K+/Na+ ratio than the wild type (WT) and KD plants. Analysis of photosynthesis and chlorophyll a fluorescence data suggested better performance of both photosystem I and II in the OsIF overexpression rice under salinity stress as compared to the WT and KD. Under salinity and high temperature stress, OsIF overexpressing plants could maintain significantly high yield, while the WT and KD plants could not. Further, metabolite profiling revealed a 2-4 fold higher accumulation of proline and trehalose in OsIF overexpressing rice than WT, under salinity stress.

Overexpression of the OsIMP Gene Increases the Accumulation of Inositol and Confers Enhanced Cold Tolerance in Tobacco through Modulation of the Antioxidant Enzymes' Activities

Inositol is a cyclic polyol that is involved in various physiological processes, including signal transduction and stress adaptation in plants. l-myo-inositol monophosphatase (IMPase) is one of the metal-dependent phosphatase family members and catalyzes the last reaction step of biosynthesis of inositol. Although increased IMPase activity induced by abiotic stress has been reported in chickpea plants, the role and regulation of the IMP gene in rice (Oryza sativa L.) remains poorly understood. In the present work, we obtained a full-length cDNA sequence coding IMPase in the cold tolerant rice landraces in Gaogonggui, which is named as OsIMP. Multiple alignment results have displayed that this sequence has characteristic signature motifs and conserved enzyme active sites of the phosphatase super family. Phylogenetic analysis showed that IMPase is most closely related to that of the wild rice Oryza brachyantha, while transcript analysis revealed that the expression of the OsIMP is significantly induced by cold stress and exogenous abscisic acid (ABA) treatment. Meanwhile, we cloned the 5' flanking promoter sequence of the OsIMP gene and identified several important cis-acting elements, such as LTR (low-temperature responsiveness), TCA-element (salicylic acid responsiveness), ABRE-element (abscisic acid responsiveness), GARE-motif (gibberellin responsive), MBS (MYB Binding Site) and other cis-acting elements related to defense and stress responsiveness. To further investigate the potential function of the OsIMP gene, we generated transgenic tobacco plants overexpressing the OsIMP gene and the cold tolerance test indicated that these transgenic tobacco plants exhibit improved cold tolerance. Furthermore, transgenic tobacco plants have a lower level of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), and a higher content of total chlorophyll as well as increased antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), when compared to wild type (WT) tobacco plants under normal and cold stress conditions.

Development of lysosome-mimicking vesicles to study the effect of abnormal accumulation of sphingosine on membrane properties

Synthetic systems are widely used to unveil the molecular mechanisms of complex cellular events. Artificial membranes are key examples of models employed to address lipid-lipid and lipid-protein interactions. In this work, we developed a new synthetic system that more closely resembles the lysosome – the lysosome-mimicking vesicles (LMVs) – displaying stable acid-to-neutral pH gradient across the membrane. To evaluate the advantages of this synthetic system, we assessed the distinct effects of sphingosine (Sph) accumulation in membrane structure and biophysical properties of standard liposomes (no pH gradient) and in LMVs with lipid composition tuned to mimic physiological- or NPC1-like lysosomes. Ternary 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/Sphingomyelin (SM)/Cholesterol (Chol) mixtures with, respectively, low and high Chol/SM levels were prepared. The effect of Sph on membrane permeability and biophysical properties was evaluated by fluorescence spectroscopy, electrophoretic and dynamic light scattering. The results showed that overall Sph has the ability to cause a shift in vesicle surface charge, increase membrane order and promote a rapid increase in membrane permeability. These effects are enhanced in NPC1- LMVs. The results suggest that lysosomal accumulation of these lipids, as observed under pathological conditions, might significantly affect lysosomal membrane structure and integrity, and therefore contribute to the impairment of cell function.

Folding of intrinsically disordered plant LEA proteins is driven by glycerol-induced crowding and the presence of membranes

Late embryogenesis abundant (LEA) proteins are related to cellular dehydration tolerance. Most LEA proteins are predicted to have no stable secondary structure in solution, i.e., to be intrinsically disordered proteins (IDPs), but they may acquire α-helical structure upon drying. In the model plant Arabidopsis thaliana, the LEA proteins COR15A and COR15B are highly induced upon cold treatment and are necessary for the plants to attain full freezing tolerance. Freezing leads to increased intracellular crowding due to dehydration by extracellular ice crystals. In vitro, crowding by high glycerol concentrations induced partial folding of COR15 proteins. Here, we have extended these investigations to two related proteins, LEA11 and LEA25. LEA25 is much longer than LEA11 and COR15A, but shares a conserved central sequence domain with the other two proteins. We have created two truncated versions of LEA25 (2H and 4H) to elucidate the structural and functional significance of this domain. Light scattering and CD spectroscopy showed that all five proteins were largely unstructured and monomeric in dilute solution. They folded in the presence of increasing concentrations of trifluoroethanol and glycerol. Additional folding was observed in the presence of glycerol and membranes. Fourier transform infra red spectroscopy revealed an interaction of the LEA proteins with membranes in the dry state leading to a depression in the gel to liquid-crystalline phase transition temperature. Liposome stability assays revealed a cryoprotective function of the proteins. The C- and N-terminal extensions of LEA25 were important in cryoprotection, as the central domain itself (2H, 4H) only provided a low level of protection.

Drought-Induced Leaf Proteome Changes in Switchgrass Seedlings

Switchgrass (Panicum virgatum) is a perennial crop producing deep roots and thus highly tolerant to soil water deficit conditions. However, seedling establishment in the field is very susceptible to prolonged and periodic drought stress. In this study, a “sandwich” system simulating a gradual water deletion process was developed. Switchgrass seedlings were subjected to a 20-day gradual drought treatment process when soil water tension was increased to 0.05 MPa (moderate drought stress) and leaf physiological properties had expressed significant alteration. Drought-induced changes in leaf proteomes were identified using the isobaric tags for relative and absolute quantitation (iTRAQ) labeling method followed by nano-scale liquid chromatography mass spectrometry (nano-LC-MS/MS) analysis. Additionally, total leaf proteins were processed using a combinatorial library of peptide ligands to enrich for lower abundance proteins. Both total proteins and those enriched samples were analyzed to increase the coverage of the quantitative proteomics analysis. A total of 7006 leaf proteins were identified, and 257 (4% of the leaf proteome) expressed a significant difference (p < 0.05, fold change <0.6 or >1.7) from the non-treated control to drought-treated conditions. These proteins are involved in the regulation of transcription and translation, cell division, cell wall modification, phyto-hormone metabolism and signaling transduction pathways, and metabolic pathways of carbohydrates, amino acids, and fatty acids. A scheme of abscisic acid (ABA)-biosynthesis and ABA responsive signal transduction pathway was reconstructed using these drought-induced significant proteins, showing systemic regulation at protein level to deploy the respective mechanism. Results from this study, in addition to revealing molecular responses to drought stress, provide a large number of proteins (candidate genes) that can be employed to improve switchgrass seedling growth and establishment under soil drought conditions (Data are available via ProteomeXchange with identifier PXD004675).

Bioactive constituents in liposomes incorporated in orange juice as new functional food: thermal stability, rheological and organoleptic properties

Liposomes were developed with bioactive constituents (omega-3, omega-6, tocopherol) incorporated in acid food. They were made of soy phosphatidylcholine (SPC) allowing the encapsulation of antioxidant vitamin C (VC) and tocopherol. Stearic acid (SA) or calcium stearate (CaS) was added as a bilayer stabilizer. The structural and oxidative stability of the liposomes were studied considering the heat effect of pasteurization. Size was analyzed by light scattering; shape and structure were studied by optical and transmission electron microscopy, respectively. Membrane packing was studied with merocyanine 540. Surface charge and oxidative stability were analyzed by zeta potential and ORAC method, respectively. The liposomes showed significant stability in all of the parameters mentioned above and an important protective effect over thermolabile VC. To confirm their applicability in food, the rheological behavior and a sensory evaluation of liposomes with vitamin C and bioactive constituents were studied. The sensory evaluation of liposomes in orange juice was performed by the overall acceptability and triangular tests with 40 and 78 potential consumers, respectively. The incorporation of all liposomal formulation did not change the acceptability of orange juice. Noteworthy, SPC and SPC:SA systems had rheological behavior similar to a Newtonian fluid whereas that SPC:CaS presented a pseudoplastic one, both considered excellent for larger scale production. From all the obtained results, we can conclude that these liposomal formulations are suitable for food industry applications, incorporating bioactive constituents and generating functional orange juice that conserves its bioactivity after pasteurization.

Biological lipid membranes for on-demand, wireless drug delivery from thin, bioresorbable electronic implants

On-demand, localized release of drugs in precisely controlled, patient-specific time sequences represents an ideal scenario for pharmacological treatment of various forms of hormone imbalances, malignant cancers, osteoporosis, diabetic conditions and others. We present a wirelessly operated, implantable drug delivery system that offers such capabilities in a form that undergoes complete bioresorption after an engineered functional period, thereby obviating the need for surgical extraction. The device architecture combines thermally actuated lipid membranes embedded with multiple types of drugs, configured in spatial arrays and co-located with individually addressable, wireless elements for Joule heating. The result provides the ability for externally triggered, precision dosage of drugs with high levels of control and negligible unwanted leakage, all without the need for surgical removal. In vitro and in vivo investigations reveal all of the underlying operational and materials aspects, as well as the basic efficacy and biocompatibility of these systems.

Binding of a ruthenium complex to a thioether ligand embedded in a negatively charged lipid bilayer: a two-step mechanism

The interaction between the ruthenium polypyridyl complex [Ru(terpy)(dcbpy)(H2O)](2+) (terpy = 2,2';6',2"-terpyridine, dcbpy = 6,6'-dichloro-2,2'-bipyridine) and phospholipid membranes containing either thioether ligands or cholesterol were investigated using UV-visible spectroscopy, Langmuir-Blodgett monolayer surface pressure measurements, and isothermal titration calorimety (ITC). When embedded in a membrane, the thioether ligand coordinated to the dicationic metal complex only when the phospholipids of the membrane were negatively charged, that is, in the presence of attractive electrostatic interaction. In such a case coordination is much faster than in homogeneous conditions. A two-step model for the coordination of the metal complex to the membrane-embedded sulfur ligand is proposed, in which adsorption of the complex to the negative surface of the monolayers or bilayers occurs within minutes, whereas formation of the coordination bond between the surface-bound metal complex and ligand takes hours. Finally, adsorption of the aqua complex to the membrane is driven by entropy. It does not involve insertion of the metal complex into the hydrophobic lipid layer, but rather simple electrostatic adsorption at the water-bilayer interface.

Contribution of galactoglycerolipids to the 3-dimensional architecture of thylakoids

Thylakoid membranes, the universal structure where photosynthesis takes place in all oxygenic photosynthetic organisms from cyanobacteria to higher plants, have a unique lipid composition. They contain a high fraction of 2 uncharged glycolipids, the galactoglycerolipids mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), and an anionic sulfolipid, sulfoquinovosediacylglycerol (SQDG). A remarkable feature of the evolution from cyanobacteria to higher plants is the conservation of MGDG, DGDG, SQDG, and phosphatidylglycerol (PG), the major phospholipid of thylakoids. Using neutron diffraction on reconstituted thylakoid lipid extracts, we observed that the thylakoid lipid mixture self-organizes as a regular stack of bilayers. This natural lipid mixture was shown to switch from hexagonal II toward lamellar phase on hydration. This transition and the observed phase coexistence are modulated by the fine-tuning of the lipid profile, in particular the MGDG/DGDG ratio, and by the hydration. Our analysis highlights the critical role of DGDG as a contributing component to the membrane stacking via hydrogen bonds between polar heads of adjacent bilayers. DGDG interactions balance the repulsive electrostatic contribution of the charged lipids PG and SQDG and allow the persistence of regularly stacked membranes at high hydration. In developmental contexts or in response to environmental variations, these properties can contribute to the highly dynamic flexibility of plastid structure.

Drought, salt, and temperature stress-induced metabolic rearrangements and regulatory networks

Plants regularly face adverse growth conditions, such as drought, salinity, chilling, freezing, and high temperatures. These stresses can delay growth and development, reduce productivity, and, in extreme cases, cause plant death. Plant stress responses are dynamic and involve complex cross-talk between different regulatory levels, including adjustment of metabolism and gene expression for physiological and morphological adaptation. In this review, information about metabolic regulation in response to drought, extreme temperature, and salinity stress is summarized and the signalling events involved in mediating stress-induced metabolic changes are presented.

Anionic liposomes increase the efficiency of adenovirus-mediated gene transfer to coxsackie-adenovirus receptor deficient cells

Despite remarkable progress in the research of both viral and nonviral gene delivery vectors, the drawbacks in each delivery system have limited their clinical applications. Therefore, one of the concepts for developing novel vectors is to overcome the limitations of individual vectors by combining them. In the current study, adenoviral vectors were formulated with anionic liposomes to protect them from neutralizing antibodies and to improve their transduction efficiency in Coxsackievirus-adenovirus receptor (CAR) deficient cells. A calcium-induced phase change method was applied to encapsulate adenovirus 5 (Ad5) into anionic liposomes to formulate the complexes of Ad5 and anionic liposomes (Ad5-AL). Meanwhile, the complexes of Ad5 and cationic liposomes (Ad5-CL) were also prepared as controls. LacZ gene expression in CAR overexpressing cells (A549) and CAR deficient cells (CHO and MDCK) was measured by either qualitative or quantitative detection. Confocal laser scanning microscopy was performed to determine intracellular location of Ad5 after their infection. Human sera with a high titer of antiadenovirus antibody were used to assess the neutralizing antibody protection ability of the complexed vectors. Accompanying the enhanced gene expression, a high ability to introduce Ad5 into cytoplasm and nucleus mediated by Ad5-AL was also observed in CAR deficient cells. Additionally, antibody neutralizing assay indicated that neutralizing serum inhibited naked Ad5 and Ad5-CL at rather higher dilution than Ad5-AL, which demonstrated Ad5-AL was more capable of protecting Ad5 from neutralizing than Ad5-CL. In conclusion, anionic liposomes prepared by the calcium-induced phase change method could significantly enhance the transduction ability of Ad5 in CAR deficient cells.

Effects of alpha-tocopherol (vitamin E) on the stability and lipid dynamics of model membranes mimicking the lipid composition of plant chloroplast membranes

Tocopherol (vitamin E) is widely recognized as a cellular antioxidant. It is essential for human and animal health, but only synthesized in photosynthetic organisms, where it is localized in chloroplast membranes. While many studies have investigated non-antioxidative effects of tocopherol on phospholipid membranes, nothing is known about its effects on membranes containing chloroplast glycolipids. Here, liposomes resembling plant chloroplast membranes were used to investigate the effects of alpha-tocopherol on vesicle stability during freezing and on lipid dynamics. alpha-Tocopherol had a pronounced influence on membrane dynamics and showed strong interactions in its effects on membrane stability during freezing with the cryoprotectant sucrose. alpha-Tocopherol showed maximal effects at low concentrations (around 2mol%), close to its contents in chloroplast membranes.

Antibody-conjugated soybean oil-filled calcium phosphate nanoshells for targetted delivery of hydrophobic molecules

Hollow calcium phosphate nanoparticles capable of encapsulating poorly water-soluble molecules were produced by self-assembly. Previously reported were solid calcium phosphate nanoparticles and water-filled calcium phosphate nanocapsules suited for encapsulating mostly hydrophilic, but not hydrophobic compounds. Here, calcium phosphate was deposited around 100 nm diameter, 1,2-dioleoyl-sn-glycero-3-phosphate stabilized soybean oil nanoemulsions using either calcium chloride or NaOH titrations to achieve shell thickness between 20-70 nm. The surface was functionalized with carboxylic acid via the addition of carboxyethylphosphonic acid to attach Molecular Probes AB-594C antibody using sulpho-n-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride with an efficiency of approximately 70%, while retaining near complete antibody function. Hydrophobic pyrene was encapsulated with an efficiency of 95%, at concentrations much higher than its water solubility limit, and exhibited spectral features characteristic of a hydrophobic environment. These materials can be used in the targeted delivery of many useful, yet poorly water-soluble pharmaceutical and nutraceutical compounds.

Formulation and optimization of piroxicam proniosomes by 3-factor, 3-level Box-Behnken design

The aim of this study was to investigate the combined influence of 3 independent variables in the preparation of piroxicam proniosomes by the slurry method. A 3-factor, 3-level Box-Behnken design was used to derive a second-order polynomial equation and construct contour plots to predict responses. The independent variables selected were molar ratio of Span 60:cholesterol (X(1)), surfactant loading (X(2)), and amount of drug (X(3)). Fifteen batches were prepared by the slurry method and evaluated for percentage drug entrapment (PDE) and vesicle size. The transformed values of the independent variables and the PDE (dependent variable) were subjected to multiple regression to establish a full-model second-order polynomial equation. F was calculated to confirm the omission of insignificant terms from the full-model equation to derive a reduced-model polynomial equation to predict the PDE of proniosome-derived niosomes. Contour plots were constructed to show the effects of X(1), X(2) and X(3) on the PDE. A model was validated for accurate prediction of the PDE by performing checkpoint analysis. The computer optimization process and contour plots predicted the levels of independent variables X(1), X(2), and X(3) (0, -0.158 and -0.158 respectively), for maximized response of PDE with constraints on vesicle size. The Box-Behnken design demonstrated the role of the derived equation and contour plots in predicting the values of dependent variables for the preparation and optimization of piroxicam proniosomes.

Stability study of stavudine-loaded O-palmitoyl-anchored carbohydrate-coated liposomes

The purpose of this study was to evaluate the physicochemical stability of carbohydrate-anchored liposomes. In the present study, carbohydrate (galactose, fucose, and mannose) was palmitoylated and anchored on the surface of positively charged liposomes (PL). The stabilities of plain neutral liposomes (NL), PL, and O-palmitoyl carbohydrate-anchored liposomes were determined. The effects of storage conditions (4 degrees C +/- 2 degrees C, 25 degrees C +/- 2 degrees C/60% +/- 5% relative humidity [RH], or 40 degrees C +/- 2 degrees C/75% +/- 5% RH for a period of 10, 20, and 30 days) were observed on the vesicle size, shape, zeta potential, drug content, and in vitro ligand agglutination assay by keeping the liposomal formulations in sealed amber-colored vials (10-mL capacity) after flushing with nitrogen. The stability of liposomal formulations was found to be temperature dependent. All the liposomal formulations were found to be stable at 4 degrees C +/- 2 degrees C up to 1 month. Storage at 25 degrees C +/- 2 degrees C/60% +/- 5% RH and 40 degrees C +/- 2 degrees C/75% +/- 5% RH adversely affected uncoated liposomal formulations. Carbohydrate coating of the liposomes could enhance the stability of liposomes at 25 degrees C +/- 2 degrees C/60% +/- 5% RH and 40 degrees C +/- 2 degrees C/75% +/- 5% RH.

Association free energy of dipalmitoylphosphatidylserines in a mixed dipalmitoylphosphatidylcholine membrane

Blood coagulation is strongly dependent on the binding of vitamin K-dependent proteins to cell membranes containing phosphatidylserine (PS) via gamma-carboxyglutamic acid (Gla) domains. The process depends on calcium, which can induce nonideal behavior in membranes through domain formation. Such domain separation mediated by Ca(2+) ions or proteins can have an important contribution to the thermodynamics of the interaction between charged peripheral proteins and oppositely charged membranes. To characterize the properties of lipid-lipid interactions, molecular dynamics, and free energy simulations in a mixed bilayer membrane containing dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine were carried out. The free energy of association between dipalmitoylphosphatidylserines in the environment of dipalmitoylphosphatidylcholines has been calculated by using a novel approach to the dual topology technique of the PS-PC hybrid. Two different methods, free energy perturbation and thermodynamic integration, were used to calculate the free energy difference. In thermodynamic integration runs three schemes were applied to evaluate the integral at the limits of lambda --> 0 or lambda --> 1. Our studies show that the association of two PSs in the environment of PCs is repulsive in the absence of Ca(2+) and becomes favorable in their presence. We also show that the mixed component membrane should exhibit nonideal behavior that will lead to PS clustering.

High concentrations of the compatible solute glycinebetaine destabilize model membranes under stress conditions

Compatible solutes are accumulated by diverse organisms in response to environmental stresses such as drought, salt, or cold. Glycinebetaine (Bet) is such a solute that is accumulated by many plants and microorganisms to high concentrations under stress conditions. It is an osmoprotectant in bacteria and stabilizes both soluble and peripherally membrane-bound proteins in vitro. Here, the effects of Bet on the stability of model lipid membranes are compared to the effects of two other compatible solutes, sucrose and trehalose. Both in the presence of 1M NaCl and during freezing to -20 degrees C, Bet is highly destabilizing to liposomes containing nonbilayer lipids, while the disaccharides are either protective or, in some cases, much less destabilizing. The destabilizing effect of Bet is more pronounced in membranes containing the nonbilayer galactolipid monogalactosyldiacylglycerol from plant chloroplasts than in membranes containing the nonbilayer phospholipid phosphatidylethanolamine. The most dramatic differences between the sugars and Bet were observed in liposomes made from a combination of lipids resembling plant chloroplast thylakoid membranes. Measurements with the dye merocyanine 540 indicate that the water-membrane interface was affected in opposite directions by the presence of high concentrations of sucrose or Bet. The dynamics of the lipids, however, were not differentially affected by the solutes, making direct solute-lipid interactions an unlikely explanation for the different effects on stability. The data offer an explanation, why Bet at high concentrations achieved during exogenous feeding of leaf tissues can be detrimental to cellular stability and survival under stress, while bacterial membranes that contain phosphatidylethanolamine instead of monogalactosyldiacylglycerol, or cyanobacteria that contain highly saturated monogalactosyldiacylglycerol are less susceptible.

Liposomal nanocapsules in food science and agriculture

Liposomes, spherical bilayer vesicles from dispersion of polar lipids in aqueous solvents, have been widely studied for their ability to act as drug delivery vehicles by shielding reactive or sensitive compounds prior to release. Liposome entrapment has been shown to stabilize encapsulated, bioactive materials against a range of environmental and chemical changes, including enzymatic and chemical modification, as well as buffering against extreme pH, temperature, and ionic strength changes. Liposomes have been especially useful to researchers in studies of various physiological processes as models of biological membranes in both eukaryotes and prokaryotes. Industrial applications include encapsulation of pharmaceuticals and therapeutics, cosmetics, anti-cancer and gene therapy drugs. In the food industry, liposomes have been used to deliver food flavors and nutrients and more recently have been investigated for their ability to incorporate food antimicrobials that could aid in the protection of food products against growth of spoilage and pathogenic microorganisms. In this review we briefly introduce key physicochemical properties of liposomes and review competing methods for liposome production. A survey of non-agricultural and food applications of liposomes are given. Finally, a detailed up-to-date summary of the emerging usage of liposomes in the food industry as delivery vehicles of nutrients, nutraceuticals, food additives, and food antimicrobials is provided.

Determination of liposome size: A tool for protein reconstitution

Reconstitution of proteins into liposomes is a widespread approach to analyzing their biological function. Many protocols exist for this procedure and for the subsequent analysis of proteins. Here, we establish a procedure for preparation and analysis of liposomes with a lipid composition reflecting the outer envelope of chloroplasts. First, the stability of the liposomes in different buffer systems was investigated to provide information for the storage of the reconstituted system. Then, the size of the liposomes created by filtration through a polycarbonate filter dependent on the lipid composition was analyzed. Subsequently, solubilization of the liposomes composed of lipids with the outer envelope composition by dodecylmaltoside and octylglucoside as a preceding step of reconstitution was studied. Finally, we developed a straightforward method to determine the size of liposomes by absorption spectroscopy. The described setup allows the construction of reconstitution protocols, including the final determination of the liposome size.

The evolutionarily related beta-barrel polypeptide transporters from Pisum sativum and Nostoc PCC7120 contain two distinct functional domains

Several beta-barrel-type channels are involved in the translocation or assembly of outer membrane proteins of bacteria or endosymbiotically derived organelles. Here we analyzed the functional units of the beta-barrel polypeptide transporter Toc75 (translocon in outer envelope of chloroplasts) of the outer envelope of chloroplasts and of a protein, alr2269, from Nostoc PCC7120 with homology to Toc75, both proteins having a similar domain organization. We demonstrated that the N-terminal region functions as a recognition and complex assembly unit, whereas the C terminus forms the beta-barrel-type pore. The pore region is, in turn, modulated by the N terminus of the proteins. The protein from Nostoc PCC7120, which shares a common ancestor with Toc75, is able to recognize precursor proteins destined for chloroplasts. In contrast, the recognition of peripheral translocon subunits by Toc75 is a novel feature acquired through evolution.

Effects of the sugar headgroup of a glycoglycerolipid on the phase behavior of phospholipid model membranes in the dry state

Glycolipids are important components of almost all biological membranes. They possess unique properties that have only been incompletely characterized so far. The plant glycolipid digalactosyldiacylglycerol (DGDG) strongly influences the physical behavior of phospholipid model membranes in both the dry and hydrated state. It was, however, unclear whether the strong effect of DGDG on the gel to liquid-crystalline phase transition temperature (Tm) in dry phosphatidylcholine (PC) bilayers is mainly due to the high degree of unsaturation of the DGDG fatty acyl chains or to interactions between the DGDG and PC headgroups. Also, no information on the relative effectiveness of membrane bound and free sugars on membrane phase behavior was available. We have used Fourier-transform infrared spectroscopy (FTIR) to investigate the phase properties and H-bonding patterns in dry membranes made from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) containing one saturated and one monounsaturated (16:0/18:1) fatty acid and different fractions of DGDG or 1,2-dilinolenoyl-sn-glycero-3-phosphatidylcholine (DLPC) (18:3/18:3). This was compared to the effects of galactose (Gal) and digalactose (diGal). All additives depressed Tm of the dry membranes, but DGDG was much more effective than DLPC or Gal. diGal had a similar effect as DGDG, pointing to the sugar headgroup as the component with the strongest influence on membrane phase behavior. A combination of DLPC and diGal, which should theoretically be equivalent to DGDG, was much more effective than the galactolipid. H-bonding interactions with the P = O group of PC were also stronger for free diGal than for DGDG, indicating that the free sugar may be structurally more flexible to adopt an optimal conformation for interactions with the PC headgroup.

Specific interactions of tryptophan with phosphatidylcholine and digalactosyldiacylglycerol in pure and mixed bilayers in the dry and hydrated state

Amphiphilic solutes play an important role in the desiccation tolerance of plant cells, because they can reversibly partition into cellular membranes during dehydration. Their effects on membrane stability depend on their chemical structure, but also on the lipid composition of the host membrane. We have shown recently that tryptophan destabilizes liposomes during freezing. The degree of destabilization depends on the presence of glycolipids in the membranes, but not on the phase preference (bilayer or non-bilayer) of the lipids in mixtures with the bilayer lipid phosphatidylcholine. Here, we have investigated the influence of tryptophan on the phase behavior and intermolecular interactions in dry and hydrated bilayers made from the phospholipid egg phosphatidylcholine and the plant chloroplast glycolipid digalactosyldiacylglycerol, or from a mixture (1:1) of these lipids, using Fourier-transform infrared spectroscopy. To distinguish effects of the hydrophobic ring structure of tryptophan from those of the amino acid moiety, we also performed experiments with the hydrophilic amino acid glycine. Our data show that there are specific interactions between tryptophan and either phospholipid or glycolipid in the dry state, as well as H-bonding interactions between the lipids and both solutes. In the rehydrated state, the H-bonding interactions between amino acids and lipids are mostly replaced by interactions between water and lipids, while the hydrophobic interactions between lipids and tryptophan mostly persist.

Phosphatidylglycerol is essential for oligomerization of photosystem I reaction center

Our earlier studies with the pgsA mutant of Synechocystis PCC6803 demonstrated the important role of phosphatidylglycerol (PG) in PSII dimer formation and in electron transport between the primary and secondary electron-accepting plastoquinones of PSII. Using a long-term depletion of PG from pgsA mutant cells, we could induce a decrease not only in PSII but also in PSI activity. Simultaneously with the decrease in PSI activity, dramatic structural changes of the PSI complex were detected. A 21-d PG depletion resulted in the degradation of PSI trimers and concomitant accumulation of monomer PSI. The analyses of PSI particles isolated by MonoQ chromatography showed that, following the 21-d depletion, PSI trimers were no longer detectable in the thylakoid membranes. Immunoblot analyses revealed that the PSI monomers accumulating in the PG-depleted mutant cells do not contain PsaL, the protein subunit thought to be responsible for the trimer formation. Nevertheless, the trimeric structure of PSI reaction center could be restored by readdition of PG, even in the presence of the protein synthesis inhibitor lincomycin, indicating that free PsaL was present in thylakoid membranes following the 21-d PG depletion. Our data suggest an indispensable role for PG in the PsaL-mediated assembly of the PSI reaction center.

The effect of hydrophobic analogues of the type I winter flounder antifreeze protein on lipid bilayers

The effect of four synthetic analogues of the 37-residue winter flounder type I antifreeze protein (AFP), which contain four Val, Ala or Ile residues in place of Thr residues at positions 2, 13, 24 and 37 and two additional salt bridges, on the binary lipid system prepared from a 1:1 mixture of the highly unsaturated DGDG and saturated DMPC has been determined using FTIR spectroscopy. In contrast to the natural protein, which increases the thermotropic phase transition, the Thr, Val and Ala analogues decreased the thermotropic phase transitions of the liposomes by 2.2 degrees Celsius, 3.4 degrees Celsius and 2.4 degrees Celsius, while the Ile analogue had no effect on the transition. Experiments performed using perdeuterated DMPC showed that the Ala and Thr peptides interacted preferentially with the DGDG in the lipid mixture, while the Val peptide showed no preference for either lipid. The results are consistent with interactions involving the hydrophobic face of type I AFPs and model bilayers, i.e. the same face of the protein that is responsible for antifreeze properties. The different effects correlate with the helicity of the peptides and suggest that the solution conformation of the peptides has a significant role in determining the effects of the peptides on thermotropic membrane phase transitions.

Intermolecular interactions in dry and rehydrated pure and mixed bilayers of phosphatidylcholine and digalactosyldiacylglycerol: a Fourier transform infrared spectroscopy study

Glycolipids are an important part of almost all biological membranes. Their effects on membrane structure and their interactions with phospholipids, however, have not been extensively studied so far. We have investigated the phase behavior and intermolecular interactions in dry and rehydrated bilayers made from the phospholipid egg phosphatidylcholine (EPC) and the plant chloroplast glycolipid digalactosyldiacylglycerol (DGDG), or from a mixture (1:1) of these lipids, using Fourier transform infrared spectroscopy. We show that there are extensive interactions between EPC and DGDG in mixed membranes, and also between DGDG molecules in pure DGDG membranes, involving sugar OH groups and C[double bond]O, P[double bond]O, and choline moieties in dry membranes. These interactions persist to a certain degree even after rehydration. We present evidence that these interactions influence the mixing behavior in phosphatidylcholine/DGDG membranes and also the phase behavior of both EPC/DGDG and pure DGDG membranes in the dry state.