Effect of Physical Parameters on the Main Phase Transition of Supported Lipid Bilayers

Abstract

Supported lipid bilayers composed of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) were assembled by the vesicle fusion technique on mica and studied by temperature-controlled atomic force microscopy. The role of different physical parameters on the main phase transition was elucidated. Both mixed (POPE/POPG 3:1) and pure POPE bilayers were studied. By increasing the ionic strength of the solution and the incubation temperature, a shift from a decoupled phase transition of the two leaflets, to a coupled transition, with domains in register, was obtained. The observed behavior points to a modulation of the substrate/bilayer and interleaflet coupling induced by the environment and preparation conditions of supported lipid bilayers. The results are discussed in view of the role of different interactions in the system. The influence of the substrate on the lipid bilayers, in terms of interleaflet coupling, can also help us in understanding the possible effect that submembrane elements like the cytoskeleton might have on the structure and dynamics of biomembranes.

Unraveling lipid/protein interaction in model lipid bilayers by Atomic Force Microscopy

“…In the latter case a strong coupling between the two leaflets could be the reason for the same lateral mobility. We recently demonstrated that the interleaflet coupling is strongly related to the experimental details of the sample preparation, including preparation temperature and the type of support (Seeger et al, 2009b;Seeger et al, 2010). So, it is not always possible to compare the obtained results even if related to the same system.…”

“…In terms of membrane protein/lipid interactions, the distribution of either GPI-anchored proteins, lipidated proteins or transmembrane proteins in the presence of phase separation in lipid bilayers is particularly relevant for understanding trafficking processes of the membrane and the possible influence of phase separation on transmembrane protein function. This topic has been studied by AFM (Milhiet et al, 2002;Seeger et al, 2009b). In the following, we will concentrate on studies performed on these types of membrane proteins.…”

Phase transition behaviors of the supported DPPC bilayer investigated by sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM)

“…(1) melting of domains (i) to (ii), i.e., (ii): 0→100%; (2) melting of domains (ii) to (iii), i.e., (iii): 0→100%, by the van't Hoff equation. 34,39,41 Assuming that the standard melting enthalpy ( H) is independent of the temperature, …”

Model Bio‐Membranes Investigated by AFM and AFS: A Suitable Tool to Unravel Lipid Organization and their Interaction with Proteins

“…Th e answer to this question requires a detailed study of the chemical-physical properties of Supported Lipid Bilayers. In this analysis we will compare the chemical-physical properties as measured with AFM on SLBs with those of other model systems [37]. We will also make use of data obtained by other techniques, especially fl uorescence techniques, on SLBs.…”

“…In light of the previous discussion on the infl uence of the support on the lipid bilayer it is straightforward to attribute the particular observed behavior to the eff ect of the solid support on the properties of the assembled planar bilayer. Figure 7.4 shows the evolution of the two phase transitions in two plots which allow to derive the van't Hoff enthalpy for each transition [37]. On the basis of this analysis and by comparing the AFM results with the thermodynamic enthalpy obtained from Diff erential Scanning Calorimetry (DSC) on liposomes of the same lipid composition it is possible to extract the average size, in terms of numbers of molecules, of the cooperative unit, which represents the number of lipids in an intrinsic domain [80].…”