Polymer-cushioned bilayers. I. A structural study of various preparation methods using neutron reflectometry.

This neutron reflectometry study evaluates the structures resulting from different methods of preparing polymer-cushioned lipid bilayers. Four different techniques to deposit a dimyristoylphosphatidylcholine (DMPC) bilayer onto a polyethylenimine (PEI)-coated quartz substrate were examined: 1) vesicle adsorption onto a previously dried polymer layer; 2) vesicle adsorption onto a bare substrate, followed by polymer adsorption; and 3, 4) Langmuir-Blodgett vertical deposition of a lipid monolayer spread over a polymer-containing subphase to form a polymer-supported lipid monolayer, followed by formation of the outer lipid monolayer by either 3) horizontal deposition of the lipid monolayer or 4) vesicle adsorption. We show that the initial conditions of the polymer layer are a critical factor for the successful formation of our desired structure, i.e., a continuous bilayer atop a hydrated PEI layer. Our desired structure was found for all methods investigated except the horizontal deposition. The interaction forces between these polymer-supported bilayers are investigated in a separate paper (Wong, J. Y., C. K. Park, M. Seitz, and J. Israelachvili. 1999. Biophys. J. 77:1458-1468), which indicate that the presence of the polymer cushion significantly alters the interaction potential. These polymer-supported bilayers could serve as model systems for the study of transmembrane proteins under conditions more closely mimicking real cellular membrane environments.     

ESR spectral analysis of the molecular motion of spin labels in lipid bilayers and membranes based on a model in terms of two angular motional parameters and rotational correlation times.

Electron spin resonance (ESR) spectral line shapes are calculated for a nitroxide spin-labeled molecule undergoing rapid restricted rotations (twisting) about its long molecular axis while simultaneously tumbling within a cone. Explicit expressions are derived for the hyperfine splittings and g-values, as well as for the secular contributions to the motionally modulated linewidths. The present model is useful for analyzing the restricted twisting and tumbling motions, and rotational correlation times, of spin-labeled molecules in bilayers. Simulated spectra compare well with experimental spectra of lecithin bilayers marked with cholestane spin label, over a wide temperature range.     

Neurocognitive Function in HIV Infected Patients on Antiretroviral Therapy

Objective

To describe factors associated with neurocognitive (NC) function in HIV-positive patients on stable combination antiretroviral therapy.

Design

We undertook a cross-sectional analysis assessing NC data obtained at baseline in patients entering the Protease-Inhibitor-Monotherapy-Versus-Ongoing-Triple therapy (PIVOT) trial.

Main outcome measure

NC testing comprised of 5 domains. Raw results were z-transformed using standard and demographically adjusted normative datasets (ND). Global z-scores (NPZ-5) were derived from averaging the 5 domains and percentage of subjects with test scores >1 standard deviation (SD) below population means in at least two domains (abnormal Frascati score) calculated. Patient characteristics associated with NC results were assessed using multivariable linear regression.

Results

Of the 587 patients in PIVOT, 557 had full NC results and were included. 77% were male, 68% Caucasian and 28% of Black ethnicity. Mean (SD) baseline and nadir CD4+ lymphocyte counts were 553(217) and 177(117) cells/µL, respectively, and HIV RNA was <50 copies/mL in all. Median (IQR) NPZ-5 score was −0.5 (−1.2/−0) overall, and −0.3 (−0.7/0.1) and −1.4 (−2/−0.8) in subjects of Caucasian and Black ethnicity, respectively. Abnormal Frascati scores using the standard-ND were observed in 51%, 38%, and 81%, respectively, of subjects overall, Caucasian and Black ethnicity (p<0.001), but in 62% and 69% of Caucasian and Black subjects using demographically adjusted-ND (p = 0.20). In the multivariate analysis, only Black ethnicity was associated with poorer NPZ-5 scores (P<0.001).

Conclusions

In this large group of HIV-infected subjects with viral load suppression, ethnicity but not HIV-disease factors is closely associated with NC results. The prevalence of abnormal results is highly dependent on control datasets utilised.

Trial registry

ClinicalTrials.gov, {"type":"clinical-trial","attrs":{"text":"NCT01230580","term_id":"NCT01230580"}}NCT01230580     

Modern evolution of a single-copy gene: the immunoglobulin C kappa locus in wild mice

The immunoglobulin kappa light-chain constant region gene (C kappa) has been cloned and sequenced from five wild mouse species. Analysis of these data has permitted an assessment of single-copy gene evolution during a limited time period as defined by the genus Mus. Sequence conservation was found to be as high (or higher) in the 5' and enhancer regions as in the coding region. The pattern of substitutions throughout these genes suggests that parallel evolution has occurred frequently and that substitutions at replacement sites have not decreased significantly, owing to saturation during this period of approximately 10 Myr. Phylogenetic relationships have been determined among these wild species as well as among members of the genus Rattus.      

A model for the packing of lipids in bilayer membranes.

A number of known structural properties of mixed lipid bilayer membranes and monolayers are accounted for by a model in which lipids pack into bilayers and monolayers like building blocks, each characterized by a surface head group area and characteristic solid angle. In phospholipids above the melting transition the head group area (at a given temperature and degree of hydration) is fairly invariant while the hydrocarbon region may be liquid-like so long as the molecule is not compressed beyond its characteristic solid angle. Phosphatidylcholine and phosphatidylserine are tapered lipids, i.e. their surface head group areas are greater than their non-polar end areas; cholesterol is frayed, i.e. its polar end area is less than its non-polar end area; while phosphatidylethanolamine is almost cylindrical. The "condensing" effect of cholesterol in mixed phospholipid-cholesterol films is seen as a taper-fray accommodation. The lipid distribution in erythrocyte membrane is shown to be conducive to a stable strain-free membrane.     

The membrane geometry of the prolamellar body

Summary When etioplasts are exposed to light, the branched tubular lattice of the prolamellar body becomes the large flat discs of the primary lamellae. We show that in spite of the very different apparent morphology of these two membranous structures, their membranes have similar average curvature and inside-outside surface areas. This implies that the packing or molecular organization of the lipids and proteins can be similar in the two structures, and that consequently the transformation does not require much high energyflip-flop of membrane components from one side to the other. We also discuss the relative physiological stability of the two structures.     

Adhesion of mussel foot protein mefp-5 to mica: an underwater superglue

Mussels have a remarkable ability to attach their holdfast, or byssus, opportunistically to a variety of substrata that are wet, saline, corroded, and/or fouled by biofilms. Mytilus edulis foot protein-5 (Mefp-5) is one of several proteins in the byssal adhesive plaque of the mussel M. edulis. The high content of 3,4-dihydroxyphenylalanine (Dopa) (～30 mol %) and its localization near the plaque-substrate interface have often prompted speculation that Mefp-5 plays a key role in adhesion. Using the surface forces apparatus, we show that on mica surfaces Mefp-5 achieves an adhesion energy approaching E(ad) = ～-14 mJ/m(2). This exceeds the adhesion energy of another interfacial protein, Mefp-3, by a factor of 4-5 and is greater than the adhesion between highly oriented monolayers of biotin and streptavidin. The adhesion to mica is notable for its dependence on Dopa, which is most stable under reducing conditions and acidic pH. Mefp-5 also exhibits strong protein-protein interactions with itself as well as with Mefp-3 from M. edulis.     

The flat-plate plant-microbial fuel cell: the effect of a new design on internal resistances

Due to a growing world population and increasing welfare, energy demand worldwide is increasing. To meet the increasing energy demand in a sustainable way, new technologies are needed. The Plant-Microbial Fuel Cell (P-MFC) is a technology that could produce sustainable bio-electricity and help meeting the increasing energy demand. Power output of the P-MFC, however, needs to be increased to make it attractive as a renewable and sustainable energy source. To increase power output of the P-MFC internal resistances need to be reduced. With a flat-plate P-MFC design we tried to minimize internal resistances compared to the previously used tubular P-MFC design. With the flat-plate design current and power density per geometric planting area were increased (from 0.15 A/m² to 1.6 A/m² and from 0.22 W/m² to and 0.44 W/m²)as were current and power output per volume (from 7.5 A/m³ to 122 A/m³ and from 1.3 W/m³ to 5.8 W/m³). Internal resistances times volume were decreased, even though internal resistances times membrane surface area were not. Since the membrane in the flat-plate design is placed vertically, membrane surface area per geometric planting area is increased, which allows for lower internal resistances times volume while not decreasing internal resistances times membrane surface area. Anode was split into three different sections on different depths of the system, allowing to calculate internal resistances on different depths. Most electricity was produced where internal resistances were lowest and where most roots were present; in the top section of the system. By measuring electricity production on different depths in the system, electricity production could be linked to root growth. This link offers opportunities for material-reduction in new designs. Concurrent reduction in material use and increase in power output brings the P-MFC a step closer to usable energy density and economic feasibility.     

Refinement of the fluid-mosaic model of membrane structure

Certain molecular packing criteria previously employed in a quantitative analysis of lipid micelles and bilayers are here extended to biological membranes. The inclusion of both thermodynamic and packing considerations point to a highly complex self-assembly mechanism in which the organization of lipids and proteins is highly coupled, with far reaching consequences as regards the structure and function of biological membranes.