Modelling the phase equilibria in two-component membranes of phospholipids with different acyl-chain lengths

A phenomenological model is proposed to describe the membrane phase equilibria in binary mixtures of saturated phospholipids with different acyl-chain lengths. The model is formulated in terms of thermodynamic and thermomechanic properties of the pure lipid bilayers, specifically the chain-melting transition temperature and enthalpy, the hydrophobic bilayer thickness, and the lateral area compressibility modulus. The model is studied using a regular solution theory made up of a set of interaction parameters which directly identify that part of the lipid-lipid interaction which is due to hydrophobic mismatch of saturated chains of different lengths. It is then found that there is effectively a single universal interaction parameter which, in the full composition range, describes the phase equilibria in mixtures of DMPC/DPPC, DPPC/DSPC, DMPC/DSPC, and DLPC/DSPC, in excellent agreement with experimental measurements. The model is used to predict the variation with temperature and composition of the specific heat, as well as of the average membrane thickness and area in each of the phases. Given the value of the universal interaction parameter, the model is then used to predict the phase diagrams of binary mixtures of phospholipids with different polar head groups, e.g., DPPC/DPPE, DMPC/DPPE and DMPE/DSPC. By comparison with experimental results for these mixtures, it is shown that difference in acyl-chain lengths gives the major contribution to deviation from ideal mixing. Application of the model to mixtures with non-saturated lipids is also discussed.     

Interactions between carrageenans and milk proteins: a microstructural and rheological study

Gels were produced using kappa-, iota-, or hybrid-carrageenan at a low (0.2-0.25%) and a high (0.7-1.0%) dosage in skim milk. The microstructure of carrageenan and protein was observed by confocal laser scanning microscopy using direct immunostaining. Additionally, rheology was used to characterize the gels. The low kappa- and iota-carrageenan dosages resulted in gels with a fine stranded carrageenan-protein microstructure and emulsion-like inclusions, while the high dosages resulted in strongly flocculated microstructures. Hybrid-carrageenan exhibited flocculation at both dosages. When using iota- and hybrid-carrageenan at a high dosage and kappa-carrageenan at both dosages, the gel characteristics were dominated by carrageenan-carrageenan interactions. On the other hand, the gel with a low dosage of iota-carrageenan in milk was barely fusible, indicating the presence of a true coupled network. We suggest that kappa-, iota-, and hybrid-carrageenan all interact with casein micelles but that the impact of this interaction on the total gel properties varied.     

Henipavirus RNA in African Bats

Background

Henipaviruses (Hendra and Nipah virus) are highly pathogenic members of the family Paramyxoviridae. Fruit-eating bats of the Pteropus genus have been suggested as their natural reservoir. Human Henipavirus infections have been reported in a region extending from Australia via Malaysia into Bangladesh, compatible with the geographic range of Pteropus. These bats do not occur in continental Africa, but a whole range of other fruit bats is encountered. One of the most abundant is Eidolon helvum, the African Straw-coloured fruit bat.

Methodology/Principal Findings

Feces from E. helvum roosting in an urban setting in Kumasi/Ghana were tested for Henipavirus RNA. Sequences of three novel viruses in phylogenetic relationship to known Henipaviruses were detected. Virus RNA concentrations in feces were low.

Conclusions/Significance

The finding of novel putative Henipaviruses outside Australia and Asia contributes a significant extension of the region of potential endemicity of one of the most pathogenic virus genera known in humans.     

Simulation of waves in calcium models with 3D spherical geometry

Waves of calcium ions are present in fertilized eggs of many species. Models for pulse and tidal wave propagation have usually been studied in one or two spatial coordinates only. We examine in three spatial coordinates some established models, based on Ca(2+)-induced Ca(2+)-release from both (assumed) continuously or heterogeneously distributed stores of endoplasmic reticulum (ER) through channels activated by inositol triphosphate (IP(3)). With continuous IP(3) distribution decreasing radially towards the interior, we obtain concave pulse shapes for waves penetrating the interior. Concave waves are also recorded in systems with ER confined to distributions of small spheres (microdomains) inside the cell, which we simulate for front waves (tides) in bistable systems.     

Microbiological,rheological and aromaticcharacteristics of fermented Uji (an East African Sour Porridge)

Three methods for fermentation of uji were compared in laboratory trials: spontaneous, backslopping (using an inoculum from a previous fermentation) and use of a starter culture of lactic acid bacteria. Spontaneous fermentation resulted in the slowest decrease in pH, while the use of starter culture led to the lowest final pH (3.5). Coliforms were eliminated in less than 8 h using backslopping or starter culture, but increased in numbers during spontaneous fermentation. The viscosity of uji was only marginally affected by the method of fermentation. The aroma profile following spontaneous fermentation contained esters with fruity notes and ethanol and higher alcohols, while mainly organic acids was produced by fermentation with the starter culture. Backslopping led to the lowest production of almost all volatiles identified.     

Density fluctuations in saturated phospholipid bilayers increase as the acyl-chain length decreases.

A systematic computer simulation study is conducted for a model of the main phase transition of fully hydrated saturated diacyl phosphatidylcholine bilayers (DMPC, DPPC, and DSPC). With particular focus on the fluctuation effects on the thermal properties in the transition region, the study yields data for the specific heat, the lateral compressibility, and the lipid-domain size distribution. Via a simple model assumption the transmembrane passive ion permeability is derived from the lipid-domain interfacial measure. A comparative analysis of the various data shows, in agreement with a number of experiments, that the lateral density fluctuations and hence the response functions increase as the acyl-chain length is decreased.     

Allergy vaccine engineering: epitope modulation of recombinant Bet v 1 reduces IgE binding but retains protein folding pattern for induction of protective blocking-antibody responses

Human type 1 immediate allergic response symptoms are caused by mediator release from basophils and mast cells. This event is triggered by allergens aggregating preformed IgE Abs bound to the high-affinity receptor (FcepsilonRI) on these cells. Thus, the allergen/IgE interaction is crucial for the cascade leading to the allergic and anaphylactic response. Two genetically engineered forms of the white birch pollen major allergen Bet v 1 with point mutations directed at molecular surfaces have been characterized. Four and nine point mutations led to a significant reduction of the binding to human serum IgE, suggesting a mutation-induced distortion of IgE-binding B cell epitopes. In addition, the mutated allergens showed a decrease in anaphylactic potential, because histamine release from human basophils was significantly reduced. Retained alpha-carbon backbone folding pattern of the mutated allergens was indicated by x-ray diffraction analysis and circular dichroism spectroscopy. The rBet v 1 mutants were able to induce proliferation of T cell lines derived from birch pollen allergic patients. The stimulation indices were similar to the indices of nonmutated rBet v 1 and natural Bet v 1 purified from birch pollen. The ability of anti-rBet v 1 mutant specific mouse IgG serum to block binding of human serum IgE to rBet v 1 demonstrates that the engineered rBet v 1 mutants are able to induce Abs reactive with nonmodified Bet v 1. rBet v 1 mutants may constitute vaccine candidates with improved efficacy/safety profiles for safer allergy vaccination.     

Using Surface Plasmon Resonance Technology to Screen Interactions Between Exopolysaccharides and Milk Proteins

Surface plasmon resonance-based biosensors enable the interaction between biomolecules to be monitored in real time with a label-free assay format. In the present study, the technique was used to assess the interaction between exopolysaccharides (EPS) and different milk proteins. The EPS were derived from three homopolysaccharide (HoPS)-producing Lactobacilli strains; Lactobacillus sakei, Lactobacillus plantarum, and Lactobacillus salvarius. The purified milk proteins applied were β-casein, β-lactoglobulin, and κ-casein. The results show that the binding capacity depends on the pH and decreases with increasing pH. HoPS from L. salvarius and L. sakei provided the highest binding response and interacted with κ-casein at all the tested pH values, i.e. in the range 4.0−5.5, and with β-casein at pH 4.0−5.0. When examined at pH 4.0, only HoPS from L. salvarius and L. sakei interacted with β-lactoglobulin. Under the tested conditions, HoPS from L. plantarum showed always either a lower binding response or no binding at all compared with HoPS from L. salvarius and L. sakei.     

A tissue-specific approach to the analysis of metabolic changes in Caenorhabditis elegans

The majority of metabolic principles are evolutionarily conserved from nematodes to humans. Caenorhabditis elegans has widely accelerated the discovery of new genes important to maintain organismic metabolic homeostasis. Various methods exist to assess the metabolic state in worms, yet they often require large animal numbers and tend to be performed as bulk analyses of whole worm homogenates, thereby largely precluding a detailed studies of metabolic changes in specific worm tissues. Here, we have adapted well-established histochemical methods for the use on C. elegans fresh frozen sections and demonstrate their validity for analyses of morphological and metabolic changes on tissue level in wild type and various mutant strains. We show how the worm presents on hematoxylin and eosin (H&E) stained sections and demonstrate their usefulness in monitoring and the identification of morphological abnormalities. In addition, we demonstrate how Oil-Red-O staining on frozen worm cross-sections permits quantification of lipid storage, avoiding the artifact-prone fixation and permeabilization procedures of traditional whole-mount protocols. We also adjusted standard enzymatic stains for respiratory chain subunits (NADH, SDH, and COX) to monitor metabolic states of various C. elegans tissues. In summary, the protocols presented here provide technical guidance to obtain robust, reproducible and quantifiable tissue-specific data on worm morphology as well as carbohydrate, lipid and mitochondrial energy metabolism that cannot be obtained through traditional biochemical bulk analyses of worm homogenates. Furthermore, analysis of worm cross-sections overcomes the common problem with quantification in three-dimensional whole-mount specimens.     

Lake restoration using a reed swamp to remove nutrients from non-point sources

The reed swamp adjacent to Lake Glumsø was partly separated from the lake by a dam and the inflow to the reed swamp controlled by pumping from the tributary. An investigation of the nutrient balances for the reed swamp showed an average daily denitrification rate of 252 mg/m2 from August 1988 to March 1989. Mineralization of the peat took place simultaneously, in sufficient amounts to supply carbon for the denitrification process. Ammonia and phosphorus were released in the ratio 7:1, corresponding to 111 mg N and 16 mg P/m²/ day. Most of the ammonia was nitrified and denitrified (included in the above mentioned denitrification rate). The net release of phosphorus implies that the method only can be applied satisfactorily in situations where nitrogen is the limiting nutrient. This is the case for Lake Glumso during the summer period, but not during the spring.This paper was presented at the INTECOL IV International Wetlands Conference in Columbus, Ohio, 1992, as part of a session organized by Prof. S. E. Jørgensen and sponsored by the International Lake Environment Committee.Corresponding Editor: Prof K. R. Reddy