Lipid bilayers

In order to mimic the surface of parenteral nutrition emulsion droplets, the first molecular dynamics simulation of a palmitoyloleoylphosphatidylcholine (POPC) monolayer at a water/triglyceride (trilinoleoylglycerol, LLL) interface was performed. Triglyceride influence was evaluated by comparing computed phospholipid properties to the ones in a similarly modelled hydrated POPC bilayer. As expected, polar head properties (molecular area, lipid hydration, headgroup orientation) were not affected by triglycerides. In contrast, slight differences were observed on phospholipid alkyl tail region (order parameter, diffusion, Van der Waals interactions). This first approach can reasonably be extended to a further more realistic multicomponent model of clinical nutrition emulsions.

Aligned stacks of monomethyl and dimethyl dimyristoyl phosphatidylethanolamine (DMPE) lipid bilayers, like the much studied dimyristoyl PC (DMPC) bilayers, swell anomalously in a critical fashion as the temperature is decreased within the fluid phase towards the main transition temperature, T(M). Unlike DMPC bilayers, both monomethyl and dimethyl DMPE undergo transitions into a gel phase rather than a rippled phase below T(M). Although it is not fully understood why there is anomalous swelling, our present results should facilitate theory by showing that the formation of the phase below T(M) is not related to critical phenomena above T(M).

FP-A and FP-B are LDPs produced by the plant pathogen Pseudomonas fuscovaginae. As expected from their primary structure, they shared a similar mechanism of action with the better characterized SPs, synthesized by strains of Pseudomonas syringae pv. syringae. Indeed, they displayed hemolytic activity on human erythrocytes and were able to induce calcein release from LUVs: the effect was dependent on the concentration of the FPs and the lipid composition of the liposome and, in particular, it increased with the SM content of the membrane. The permeabilizing activity was further investigated on PLMs. FPs were able to open pores on pure POPC membranes. Pore opening was strongly voltage dependent: by switching the potential from negative to positive values, an increase in the absolute amplitude of transmembrane current was induced with simultaneous closure of pores. In 0.1 M KCl both FPs' pores had a conductance of 4 and 9 pS at − 140 mV and + 140 mV, respectively. Studies on ion selectivity indicated that FPs formed cation-selective channels. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd.

δ-Helices are marginally hydrophobic α-helical segments in soluble proteins that exhibit certain sequence characteristics of transmembrane (TM) helices [Cunningham, F., Rath, A., Johnson, R. M. & Deber, C. M. (2009). Distinctions between hydrophobic helices in globular proteins and TM segments as factors in protein sorting. J. Biol. Chem., 284, 5395–402]. In order to better understand the difference between δ-helices and TM helices, we have studied the insertion of five TM-like δ-helices into dog pancreas microsomal membranes. Using model constructs in which an isolated δ-helix is engineered into a bona fide membrane protein, we find that, for two δ-helices originating from secreted proteins, at least three single-nucleotide mutations are necessary to obtain efficient membrane insertion, whereas one mutation is sufficient in a δ-helix from the cytosolic protein P450BM-3. We further find that only when the entire upstream region of the mutated δ-helix in the intact cytochrome P450BM-3 is deleted does a small fraction of the truncated protein insert into microsomes. Our results suggest that upstream portions of the polypeptide, as well as embedded charged residues, protect δ-helices in globular proteins from being recognized by the signal recognition particle–Sec61 endoplasmic-reticulum-targeting machinery and that δ-helices in secreted proteins are mutationally more distant from TM helices than δ-helices in cytosolic proteins.► δ-Helices are marginally hydrophobic α-helical segments in soluble proteins that exhibit certain sequence characteristics of TM helices. ► We have studied the membrane integration potential of δ-helices selected from secreted and cytosolic proteins. ► Three mutations can turn δ-helices from secreted proteins into TM helices. ► A single mutation turns a δ-helix from a cytosolic protein into a TM helix. ► Upstream secondary structure protects hydrophobic helices from membrane integration.

We introduce a simple experimental system to study dynamics of needle-like nanoobjects in two dimensions (2D) as a function of their surface density close to the isotropic-nematic transition. Using fluorescence correlation spectroscopy, we find that translational and rotational diffusion of rigid DNA origami nanoneedles bound to freestanding lipid membranes is strongly suppressed upon an increase in the surface particle density. Our experimental observations show a good agreement with results of Monte Carlo simulations of Brownian hard needles in 2D.

Fluorescence correlation spectroscopy (FCS) is a single molecule technique used mainly for determination of mobility and local concentration of molecules. This review describes the specific problems of FCS in planar systems and reviews the state of the art experimental approaches such as 2-focus, Z-scan or scanning FCS, which overcome most of the artefacts and limitations of standard FCS. We focus on diffusion measurements of lipids and proteins in planar lipid membranes and review the contributions of FCS to elucidating membrane dynamics and the factors influencing it, such as membrane composition, ionic strength, presence of membrane proteins or frictional coupling with solid support.

The antitumoral effects of oncolytic viruses have generally been limited by inefficient spread of the viruses within infected tumors and by inefficient systemic delivery, particularly in preimmunized hosts. Tumor-selective poxviruses have biolog- ical characteristics that may overcome these limitations. Nevertheless, physical barriers within the tumor microenvi- ronment, including the extracellular matrix, can still limit intratumoral spread, and neutralizing antibodies can

Membrane proteins play crucial roles in a range of biological processes. High resolution structures provide insights into the functional mechanisms of membrane proteins, but detailed biophysical characterization of membrane proteins is difficult. Complementary to experimental techniques, molecular dynamics simulations is a powerful tool in providing more complete description of the dynamics and energetics of membrane proteins with high spatial-temporal resolution. In this chapter, we provide a survey of the current methods and technique issues for setting up and running simulations of membrane proteins. The recent progress in applying simulations to understanding various biophysical properties of membrane proteins is outlined.

The hypothesis that physiologically activeconcentrations of salicylic acid (SA) and itsderivatives can confer stress tolerance in plants wasevaluated using bean (Phaseolus vulgaris L.) andtomato (Lycopersicon esculentum L.). Plantsgrown from seeds imbibed in aqueous solutions (0.1--0.5 mM) of salicylic acid or acetyl salicylic acid(ASA) displayed enhanced tolerance to heat, chillingand drought stresses. Seedlings acquired similarstress tolerance when SA or ASA treatments wereapplied as soil drenches. The fact that seedimbibition with SA or ASA confers stress tolerance inplants is more consistent with a signaling role ofthese molecules, leading to the expression oftolerance rather than a direct effect. Induction ofmultiple stress tolerance in plants by exogenousapplication of SA and its derivatives may have asignificant practical application in agriculture,horticulture and forestry.