From Liposomes to Supported, Planar Bilayer Structures on Hydrophilic and Hydrophobic Surfaces: An Atomic Force Microscopy Study

Abstract

The sequence of events involved in the transition from attached liposomes to bilayer patches on hydrophilic and hydrophobic solid supports were visualized in situ by Tapping Mode atomic force microscopy in liquid. In a smooth manner, the attached liposomes spread and flattened from the outer edges toward the center until the two membrane bilayers were stacked on top of each other. The top bilayer then either rolls or slides over the bottom bilayer, and the adjacent edges join to form a larger membrane patch. This is clearly visible from the apparent height of 6.0-7.5 nm of the single bilayer, measured in situ. The addition of calcium appeared to increase the rate of the processes preventing the visualization of the intermediate stages. The same intermediate steps appeared to be present on hydrophobic surfaces, although the attached liposomes seemed to be distorted and the resultant membrane edges were uneven. This work has provided visual and detailed information on liposome coalescence (fusion) onto solid supports and demonstrated how the atomic force microscope can be used to study the process.

Reconstitution of Holin Activity with a Synthetic Peptide Containing the 1–32 Sequence Region of EJh, the EJ-1 Phage Holin

“…8A). These defects allowed an estimate of 5-6 nm for the thickness of the bilayer plus the water layer between the support and the contact leaflet, in agreement with previously reported data (27,38). In contrast, when the lipidpeptide assemblies were fused onto the mica, the formed bilayers displayed numerous holes of different sizes, shapes, and depths.…”

“…The supported membranes were prepared by depositing 50 l of 1 mg/ml solution of liposomes in 20 mM Hepes-HCl, pH 7.0, containing 0.1 M NaCl and 20 mM CaCl 2 on top of freshly cleaved circular pieces of mica glued onto a Teflon surface (27). The liposomes were allowed to fuse on the mica for 30 -60 min at room temperature and then extensively washed with buffer.…”

“…8). Lipid vesicles of various compositions (POPG, POPG:POPC (70:30)) in the absence and presence of EJh-L1M1 (externally added from an Me 2 SO stock solution) were fused onto freshly prepared mica surfaces using Ca 2ϩ as fusogen (27). Pure lipid bilayers, regardless of composition, were observed as smooth surfaces with statistically negligible defects (Fig.…”

Visualizing Association of N-Ras in Lipid Microdomains: Influence of Domain Structure and Interfacial Adsorption

“…13,14 To understand the role of lipid complexes and (probably transient) clusters or domains in regulating membrane properties, ternary mixtures containing cholesterol and a saturated and an unsaturated phospholipid are often chosen in model studies of rafts. Along with a number of techniques used to address questions on rafts, important contributions have come from different microscopic approaches such as two-photon excited fluorescence microscopy [18][19][20][21][22][23][24][25][26][27] and, more recently, atomic force microscopy (AFM) [28][29][30][31][32][33][34][35] for studying solid-supported membranes. The fluorescence microscopy experimentsswith a spatial resolution on the micrometer scaleson giant unilamellar vesicles (GUVs) prepared from particular three-component lipid raft mixtures indicate the coexistence of two fluid phases [liquiddisordered (l d ) and liquid-ordered (l o )].…”

Reconstituição da Anexina V em sistemas de lipossomos: associação com a fosfatase alcalina e correlação com estudos de biomineralização

“…43-B (Goksu et al, 2009;Kirat et al, 2010;Morandat et al, 2010). Poucos trabalhos apresentam lipossomos intactos, e mesmo assim são imagens com pouca nitidez (Jass et al, 2000;Ruozi et al, 2009Ruozi et al, , 2011.…”