2 research outputs found
Morphology and Physical Properties of Hydrophilic-Polymer-Modified Lipids in Supported Lipid Bilayers
Lipid
molecules such as glycolipids that are modified with hydrophilic
biopolymers participate in the biochemical reactions occurring on
cell membranes. Their functions and efficiency are determined by the
formation of microdomains and their physical properties. We investigated
the morphology and properties of domains induced by the hydrophilic-polymer-modified
lipid applying a polyethylene glycol (PEG)-modified lipid as a model
modified lipid. We formed supported lipid bilayers (SLBs) using a
0–10 mol % range of PEG-modified lipid concentration (<i>C</i><sub>PEG</sub>). We studied their morphology and fluidity
by fluorescence microscopy, the fluorescence recovery after photobleaching
method, and atomic force microscopy (AFM). Fluorescence images showed
that domains rich in the PEG-modified lipid appeared and SLB fluidity
decreased when <i>C</i><sub>PEG</sub> ≥ 5%. AFM topographies
showed that clusters of the PEG-modified lipid appeared prior to domain
formation and the PEG-lipid-rich domains were observed as depressions.
Frequency-modulation AFM revealed a force-dependent appearance of
the PEG-lipid-rich domain
Lateral Diffusion and Molecular Interaction in a Bilayer Membrane Consisting of Partially Fluorinated Phospholipids
Fluorinated lipids
and surfactants are attractive biomimetic materials
for the extraction and reorganization of membrane proteins because
of the biological inertness of fluorocarbons. We investigated the
fundamental physical properties of a partially fluorinated phospholipid
(F4-DMPC), such as phase transition, area thermal expansion, and lateral
lipid diffusion, to evaluate the intermolecular interaction of F4-DMPC
in the hydrophobic region quantitatively on the basis of free-volume
theory. Fluorescence microscope observation of the supported lipid
bilayer (SLB) of F4-DMPC showed that the phase transition between
the liquid crystalline and gel phases occurred at 5 °C and that
the area thermal expansion coefficient was independent of the temperature
near the phase transition temperature. We performed a single particle
tracking of the F4-DMPC-SLB on a SiO<sub>2</sub>/Si substrate, to
measure the diffusion coefficient and its temperature dependence.
The apparent activation energy (<i>E</i>′<sub>a</sub>) of lateral lipid diffusion, which is an indicator of intermolecular
interaction, was 39.1 kJ/mol for F4-DMPC, and 48.2 kJ/mol for a nonfluorinated
1,2-dioleoyl-<i>sn</i>-glycero-3-phosphocholine as a control.
The difference of 9 kJ/mol in <i>E</i>′<sub>a</sub> was significant compared with the difference due to the acyl chain
species among nonfluorinated phosphatidylcholine and also that caused
by the addition of cholesterol and alcohol in the bilayer membranes.
We quantitatively evaluated the attenuation of intermolecular interaction,
which results from the competition between the dipole-induced packing
effect and steric effect at the fluorocarbon segment in F4-DMPC