Determination of DMPC hydration in the Lα and Lβ′ phases by 2H solid state NMR of D2O

AbstractThe number of water molecules bound to the dimyristoylphosphatidylcholine (DMPC) interface was investigated both in the fluid (Lα) and gel (Lβ′) phases by solid state deuterium NMR of D2O. We determined that each DMPC molecule binds 9.7±0.5 and less than 4.3±0.5 D2O in the fluid and gel phases respectively. These results are accounted for by considering the number of DMPC binding sites as well as the molecular organization in each phase. ©1997 Federation of European Biochemical Societies

Measurement of the Lateral Diffusion of Dipalmitoylphosphatidylcholine Adsorbed on Silica Beads in the Absence and Presence of Melittin: A 31P Two-Dimensional Exchange Solid-State NMR Study

Abstract31P two-dimensional exchange solid-state NMR spectroscopy was used to measure the lateral diffusion, DL, in the fluid phase of dipalmitoylphosphatidylcholine (DPPC) in the presence and absence of melittin. The use of a spherical solid support with a radius of 320±20nm, on which lipids and peptides are adsorbed together, and a novel way of analyzing the two-dimensional exchange patterns afforded a narrow distribution of DL centered at a value of (8.8±0.5)×10−8cm2/s for the pure lipid system and a large distribution of DL spanning 1×10−8 to 10×10−8cm2/s for the lipids in the presence of melittin. In addition, the determination of DL for nonsupported DPPC multilamellar vesicles (MLVs) suggests that the support does not slow down the lipid diffusion and that the radii of the bilayers vary from 300 to 800nm. Finally, the DPPC-melittin complex is stabilized at the surface of the silica beads in the gel phase, opening the way to further study of the interaction between melittin and DPPC

Experiencias de la aplicación de metodologías innovadoras en la relación (proceso) enseñanza-aprendizaje

Nos proponemos por medio de la presente, relatar las diversas experiencias derivadas de la aplicación concreta de metodologías innovadoras en el proceso de formación, enseñanza-aprendizaje, llevado a cabo en el marco de la labor desarrollada en Cátedra I de la materia Finanzas y Derecho Financiero, de la Facultad de Ciencias Jurídicas y Sociales de la UNLP. Ello, a fin de efectuar oportunamente, y a modo de corolario, una serie de conclusiones.Facultad de Ciencias Jurídicas y Sociale

Key Role of Polyphosphoinositides in Dynamics of Fusogenic Nuclear Membrane Vesicles

The role of phosphoinositides has been thoroughly described in many signalling and membrane trafficking events but their function as modulators of membrane structure and dynamics in membrane fusion has not been investigated. We have reconstructed models that mimic the composition of nuclear envelope precursor membranes with naturally elevated amounts of phosphoinositides. These fusogenic membranes (membrane vesicle 1(MV1) and nuclear envelope remnants (NER) are critical for the assembly of the nuclear envelope. Phospholipids, cholesterol, and polyphosphoinositides, with polyunsaturated fatty acid chains that were identified in the natural nuclear membranes by lipid mass spectrometry, have been used to reconstruct complex model membranes mimicking nuclear envelope precursor membranes. Structural and dynamic events occurring in the membrane core and at the membrane surface were monitored by solid-state deuterium and phosphorus NMR. “MV1-like” (PC∶PI∶PIP∶PIP2, 30∶20∶18∶12, mol%) membranes that exhibited high levels of PtdIns, PtdInsP and PtdInsP2 had an unusually fluid membrane core (up to 20% increase, compared to membranes with low amounts of phosphoinositides to mimic the endoplasmic reticulum). “NER-like” (PC∶CH∶PI∶PIP∶PIP2, 28∶42∶16∶7∶7, mol%) membranes containing high amounts of both cholesterol and phosphoinositides exhibited liquid-ordered phase properties, but with markedly lower rigidity (10–15% decrease). Phosphoinositides are the first lipids reported to counterbalance the ordering effect of cholesterol. At the membrane surface, phosphoinositides control the orientation dynamics of other lipids in the model membranes, while remaining unchanged themselves. This is an important finding as it provides unprecedented mechanistic insight into the role of phosphoinositides in membrane dynamics. Biological implications of our findings and a model describing the roles of fusogenic membrane vesicles are proposed

Interactions entre les tannins et les lipides (impact possible sur le goût du vin)

Lors de la dégustation d un vin, les tannins sont responsables de deux propriétés gustatives, l amertume et l astringence, respectivement dues à des associations avec les protéines salivaires et les récepteurs au goût amer. Néanmoins, leurs intensités perçues en bouche vont dépendre de multiples facteurs, notamment la présence de molécules externes aux complexes tannin-protéine tel que les lipides, qu ils soient situés au niveau des membranes buccales ou issus de l alimentation. L objectif de cette thèse a ainsi été d examiner l impact des lipides sur ces sensations organoleptiques. Pour ce faire, cette étude, réalisée principalement par RMN, s est intéressée aux interactions tannin-lipide sur des modèles de membranes buccales et d émulsions de gouttelettes lipidiques. Nous avons pu alors étudier l interaction tannin-lipide en termes de localisation, d affinité et de dynamique. Nos résultats montrent dans un premier temps une localisation du tannin à l interface de tous les modèles utilisés. En outre, l insertion de tannins au niveau des vésicules multilamellaires, modèle utilisé pour mimer les membranes buccales, entraîne une fluidification de ce système lipidique. Il a été montré que cet effet fluidifiant dépend de la structure du tannin, de la présence d éthanol et de la teneur en cholestérol du système lipidique. Enfin, un protocole permettant d obtenir les constantes d associations tannin-lipide par RMN a été établi. Ces dernières se sont révélées du même ordre de grandeur que celles relatives aux interactions tannin-protéine salivaire. Ces résultats montrent que les lipides auraient une influence d une part sur l astringence via une compétition entre les interactions tannin-lipide et les interactions tannin-protéines salivaires et d autre part sur l amertume en perturbant la dynamique de la membrane, ce qui pourrait induire une perturbation des récepteurs gustatifs.When tasting a wine, tannins are responsible of two gustative properties, bitterness and astringency, respectively due to association between tannins and salivary proteins or bitter receptors. However, perceived intensities depend on several factors, including the presence of external molecules such as lipids, either located in the buccal membranes or from food. The main objective of this thesis was to study the effect of lipids on these two organoleptic properties. For that, this study, carried out mainly by NMR, is interested in tannin-lipid interaction using several models of buccal membranes and lipid droplets. We have studied these interactions in terms of localization, affinity and dynamics. Our results show a localization of tannins at the interface of all studied lipid models. Then, the insertion of tannins in multilamellar vesicles, used to mimic buccal membranes, causes a fluidification effect on these systems. This effect depends on the structure of the tannin, the presence of ethanol and the cholesterol content of the lipid system. Finally, a protocol to determine the tannin-lipid association constants was developed. The latter have proved to be in the same order of magnitude as those for tannin-salivary protein interaction. These results show that lipids could have an influence on the one hand on astringency, due to the competition between tannin-lipid interaction and tannin-salivary protein interaction, and on the other hand on bitterness due to the disturbance of the buccal membrane dynamics, which could induce a disturbance of the gustative receptors.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Monitoring changes of paramagnetically-shifted 31P signals in phospholipid vesicles

Phospholipid vesicles are commonly used as biomimetics in the investigation of the interaction of various species with cell membranes. In this paper we present a 31P NMR investigation of a simple vesicle system using a paramagnetic shift reagent to probe the inner and outer layers of the lipid bilayer. Time-dependent changes in the 31P NMR signal are observed, which differ whether the paramagnetic species is inside or outside the vesicle, and on the choice of buffer solution used. An interpretation of these results is given in terms of the interaction of the paramagnetic shift reagent with the lipids

Hypercholesterolemia Impaired Sperm Functionality in Rabbits

Hypercholesterolemia represents a high risk factor for frequent diseases and it has also been associated with poor semen quality that may lead to male infertility. The aim of this study was to analyze semen and sperm function in diet-induced hypercholesterolemic rabbits. Twelve adult White New Zealand male rabbits were fed ad libitum a control diet or a diet supplemented with 0.05% cholesterol. Rabbits under cholesterol-enriched diet significantly increased total cholesterol level in the serum. Semen examination revealed a significant reduction in semen volume and sperm motility in hypercholesterolemic rabbits (HCR). Sperm cell morphology was seriously affected, displaying primarily a “folded head”-head fold along the major axe-, and the presence of cytoplasmic droplet on sperm flagellum. Cholesterol was particularly increased in acrosomal region when detected by filipin probe. The rise in cholesterol concentration in sperm cells was determined quantitatively by Gas chromatographic-mass spectrometric analyses. We also found a reduction of protein tyrosine phosphorylation in sperm incubated under capacitating conditions from HCR. Interestingly, the addition of Protein Kinase A pathway activators -dibutyryl-cyclic AMP and iso-butylmethylxanthine- to the medium restored sperm capacitation. Finally, it was also reported a significant decrease in the percentage of reacted sperm in the presence of progesterone. In conclusion, our data showed that diet-induced hypercholesterolemia adversely affects semen quality and sperm motility, capacitation and acrosomal reaction in rabbits; probably due to an increase in cellular cholesterol content that alters membrane related events

Membrainy: a ‘smart’, unified membrane analysis tool

BACKGROUND: The study of biological membranes using Molecular Dynamics has become an increasingly popular means by which to investigate the interactions of proteins, peptides and potentials with lipid bilayers. These interactions often result in changes to the properties of the lipids which can modify the behaviour of the membrane. Membrainy is a unified membrane analysis tool that contains a broad spectrum of analytical techniques to enable: measurement of acyl chain order parameters; presentation of 2D surface and thickness maps; determination of lateral and axial headgroup orientations; measurement of bilayer and leaflet thickness; analysis of the annular shell surrounding membrane-embedded objects; quantification of gel percentage; time evolution of the transmembrane voltage; area per lipid calculations; and quantification of lipid mixing/demixing entropy. RESULTS: Each analytical component within Membrainy has been tested on a variety of lipid bilayer systems and was found to be either comparable to or an improvement upon existing software. For the analytical techniques that have no direct comparable software, our results were confirmed with experimental data. CONCLUSIONS: Membrainy is a user-friendly, intelligent membrane analysis tool that automatically interprets a variety of input formats and force fields, is compatible with both single and double bilayers, and capable of handling asymmetric bilayers and lipid flip-flopping. Membrainy has been designed for ease of use, requiring no installation or configuration and minimal user-input to operate