Water Replacement Hypothesis in Atomic Details: Effect of Trehalose on the Structure of Single Dehydrated POPC Bilayers

Laboratory of Plant Physiology, Wageningen University, Wageningen, The Netherlands.
Langmuir (Impact Factor: 4.46). 07/2010; 26(13):11118-26. DOI: 10.1021/la100891x
Source: PubMed


We present molecular dynamics (MD) simulations to study the plausibility of the water replacement hypothesis (WRH) from the viewpoint of structural chemistry. A total of 256 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC) lipids were modeled for 400 ns at 11.7 or 5.4 waters/lipid. To obtain a single dehydrated bilayer relevant to the WRH, simulations were performed in the NP(xy)h(z)T ensemble with h(z) > 8 nm, allowing interactions between lipids in the membrane plane and preventing interactions between neighboring membranes via periodic boundary conditions. This setup resulted in a stable single bilayer in (or near) the gel state. Trehalose caused a concentration-dependent increase of the area per lipid (APL) accompanied by fluidizing the bilayer core. This mechanism has been suggested by the WRH. However, dehydrated bilayers in the presence of trehalose were not structurally identical to fully hydrated bilayers. The headgroup vector was in a more parallel orientation in dehydrated bilayers with respect to the bilayer plane and maintained this orientation in the presence of trehalose in spite of APL increase. The total dipole potential changed sign in dehydrated bilayers and remained slightly positive in the presence of trehalose. The model of a dehydrated bilayer presented here allows the study of the mechanisms of membrane protection against desiccation by different compounds.

Download full-text


Available from: Andrey Victorovich Golovin
  • [Show abstract] [Hide abstract]
    ABSTRACT: Electron spin echo (ESE) spectroscopy, a pulsed version of electron paramagnetic resonance (EPR), was applied to spin-labeled stearic acids in phospholipid bilayers hydrated in the presence of sucrose and sorbitol, which are known for their cryoprotective action on biological membranes. The phospholipids were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Stearic acids were labeled by nitroxide 4,4-dimethyl-oxazolidine-1-oxyl (DOXYL) attached rigidly at either the 5th or 16th specific carbon positions. ESE detects fast stochastic small-angle restricted molecular rotations (stochastic molecular librations) with correlation times on the nanosecond timescale. These motions are believed to have the same nature as the anharmonic motions of hydrogen atoms in biological substances detected by neutron scattering and Mössbauer spectroscopy, which become active above 200 K. To ensure that the echo decays indeed originate from fast stochastic molecular librations, a three-pulse stimulated spin echo was employed. It was found that the presence of sucrose or sorbitol suppresses the observed molecular motions. The observed effect was nearly the same for both label positions, indicating that the motions are similarly suppressed near the bilayer surface and in the bilayer interior. This finding suggests non-specific interactions of sugars with bilayer surface, which are likely to influence only the bulk physical properties of hydrated membranes. The results obtained show the usefulness of spin-echo EPR of spin labels when applied to investigate the molecular mechanisms of action of cryoprotective agents on biological systems.
    No preview · Article · Aug 2013 · Applied Magnetic Resonance
  • [Show abstract] [Hide abstract]
    ABSTRACT: This chapter describes the most relevant practical approaches for the identification and characterization of the N-acylhomoserine lactones (AHL) family of quorum sensing signal molecules. The first indication of AHL-mediated gene regulation in a Gram-negative bacterial pathogen is the appearance of a specific phenotype in a cell density dependent fashion. This may be further evidenced by an earlier manifestation of that phenotype, when the organism is grown in the presence of some of its own filtered spent culture supernatant as a potential source of AHLs or indeed other chemically distinct signal molecules. The development of sensitive bioassays for the detection of AHLs has greatly facilitated the screening of micro-organisms for new AHL molecules. N-Acyl-L-homoserine lactones can be prepared by a carbodiimide-mediated acylation of L-homoserine lactone hydrochloride. A typical procedure is explained in the chapter.
    No preview · Article · Dec 1998 · Methods in Microbiology
  • [Show abstract] [Hide abstract]
    ABSTRACT: Integral thin film capacitors offer great potential for high density, high speed, high I/O and low voltage IC packaging. They can be used to replace discrete surface mount capacitors for bypassing, decoupling, termination and frequency determining functions. Ceramic-polymer nanocomposites constitute one of the finest options as dielectrics in the fabrication of integral thin film capacitor arrays. The dielectric behavior is influenced by particle size of the ceramic, distance between particles and ceramic/polymer interface and interphase, if any. One major challenge in understanding the electrical behavior of polymer ceramic composites is the lack of viable models describing the characteristics of the composites. In the absence of such models the ultimate materials limit/performance and direction to proceed with their synthetic design are unknown. This problem has become even more acute recently as there is a deliberate effort to use smaller and smaller ceramic particles (nanoparticles) to improve processability and produce thinner dielectric films or printing inks for direct write/screen-printing applications. With decreasing particle size the influence of the interphase region becomes more dominant. In this paper we present our work on the interfacial influence of the ultimate performance of materials/application limits in terms of dielectric constant, loss and thermal stability as a function of particle size and loading of ceramic, polymer matrix and interphase characteristics. Complex Nonlinear Least Squares (CNLS) methods employed in the network modeling of ceramic-grain boundaries has been extended to test the case of Polymer-ceramic nanocomposites
    No preview · Conference Paper · Feb 2000
Show more