Physics And Chemistry Basis Of Biotechnology - De Cuyper - tiera.ru

Britta Lindholm-Sethson
4. s-BLMs with an aqueous reservoir trapped between the solid support and the
membrane
For supported lipid bilayers intended as a model systems for natural biological
membranes where membrane proteins can be incorporated with retained activity it is
beneficial that the membrane is surrounded with an aqueous phase. When the
phospholipid layers are transferred directly onto a metal support, the membrane is only
separated from the electrode surface with an ultrathin layer of water. This water film is
sufficient to give mobility to the phospholipids in the inner leaflet of the bilayer.
However, incorporated large membrane spanning proteins are immobilised which
has an unfavourable effect on their activity. One elegant solution is the self-assembly of
lipid bilayers on agarose as developed by H.T. Tien and described in the preceding
section. However, although this method is superior in its simplicity and gives bilayer
lipid membranes facing aqueous solutions on both sides, the technology does not allow
precise manipulation of the composition of the bilayer. Moreover, the total membrane
area is small, typically with a diameter of 1 mm.
In this section I will focus on the attempts to build lipid bilayers linked to a solid
support through an aqueous phase of significant thickness. The work presented below is
divided in two sections: tethered lipid membranes and polymer cushioned lipid
membranes.
4.1, TETHERED LIPID MEMBRANES
A new class of lipids was introduced by H. Lang et al., [24,25] comprising the
attachment of a hydrophilic spacer to the phosphate group of dipalmitoylglycerophosphatidic
acid. Three ethylene glycol spacers of different lengths were employed, all
terminated with a disulfide group. Thus, these so-called “thiolipids” can be covalently
linked to a gold substrate in a simple self-assembling procedure. Various types of
monolayers and bilayers were assembled and investigated with surface plasmon
resonance and electrochemical techniques. It was found that the longer the spacer, the
higher was the molecular integrity and also the optical density of the first monolayer. A
monolayer of conventional phospholipids was spontaneously formed on top of the first
thiolipid monolayer simply by exposing it to a lipid/detergent solution which was
diluted stepwise below the critical micelle concentration of the detergent. Thus,
supported phospholipid bilayers could be formed which were mechanically and
chemically stable for several weeks. The capacitance of the planar gold-supported
membrane was in good accordance with solvent free planar unsupported black lipid
membranes and therefore these systems were proposed as most suitable aspirants for
incorporation of membrane proteins with large extramembraneous parts. In an ensuing
paper the same group reports on the formation of 2D structured surfaces based on the
combination of Langmuir-Blodgett and self-assembly techniques [ 100, 101] Briefly,
the proposed method involves Langmuir-Blodgett transfer of a mixed monolayer
consisting of phase separated palmitic acid and thiolipids to a planar gold surface. The
fatty acid was washed away after transfer, exposing bare gold domains. These 2D
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