Biology Reference
In-Depth Information
vesicle-substrate interaction. Divalent cations especially inluence the
process. For instance, adsorption of negatively charged vesicles made from
a mixture of palmitoyl-oleoyl-phosphoglycerol (POPG)/palmitoyl-oleoyl-
phosphatidylethanolamine (POPE) lipids is only possible in the presence of
calcium chloride.
12
Rupture of intact vesicles can be immediate after vesicle
adsorption on the surface or delayed until a critical coverage is reached. It
also depends on lipid composition, vesicle concentration and diameter.
8,13
The main drawback of the vesicle fusion method is the symmetry of SLBs
that are obtained and that imperfectly mimic biological membranes. Another
drawback is the partial loss of membrane dynamics due to strong interaction
between the lipid polar heads of the inner lealet and the substrate, modifying
the thickness of the buffer layer trapped between support and SLB.
Figure 1.1.
Schematic view of the formation of supported lipid bilayers using the
fusion of unilamellar vesicles. Single vesicles (lipid polar heads are in red) can adsorb
on the surface and rupture to form a supported lipid bilayer
(
SLB) (left part of the
scheme). Alternatively, vesicles can fuse together prior to the rupture (right part of
the scheme). A water layer is trapped between the lipids and the support and can act
as lubricant.
This thickness largely inluences the physical properties of the membrane.
It is, for instance, clear that divalent cations can bridge the polar heads of
lipids with mica, leading to a large decrease in the interfacial buffer layer as
recently observed with SLB composed of neutral phospholipids.
Similarly,
it was described that the way glass coverslips are cleaned largely modulates
membrane dynamics and domain formation, probably by changing the
viscosity of the water layer trapped between glass and lipid polar heads.
16
More recently, using a POPG/POPE mixture, it was demonstrated that ionic
strength largely inluences the structure of the water layer, probably by
screening the substrate surface charge and by modifying the Debye length.
14,15
The decreased thickness of the water layer could also explain decoupling
17
Search WWH ::
Custom Search