Membrane biomimetic layer

A biomolecular system of glycoproteins derived from bacterial cell envelopes that spontaneously aggregates to form crystalline arrays in the mesoscopic range is reviewed in Chapter 9. The structure and features of these S-layers that can be applied in biotechnology, membrane biomimetics, sensors, and vaccine development are discussed. 

Supported bilayers represent biomimetic layers which can be supported on a range of materials and adapted for the study of biointeractions (protein-protein, lipid-lipid) including molecular recognition, ion-channel transport and intramembrane interactions. This interface type can be separated into the so-called SLBs (supported lipid bilayers), HBMs (hybrid bilayer membranes) and t-BLMs (tethered bilayer membranes). 

In this context it is interesting to note that archaea, which possess S-layers as exclusive cell wall components outside the cytoplasmic membrane (Fig. 14), exist under extreme environmental conditions (e.g., high temperatures, hydrostatic pressure, and salt concentrations, low pH values). Thus, it is obvious one should study the effect of proteinaceous S-layer lattices on the fluidity, integrity, structure, and stability of lipid membranes. This section focuses on the generation and characterization of composite structures that mimic the supramolecular assembly of archaeal cell envelope structures composed of a cytoplasmic membrane and a closely associated S-layer. In this biomimetic structure, either a tetraether... 

FIG. 14 Schematic illustration of an archaeal cell envelope structure (a) composed of the cytoplasmic membrane with associated and integral membrane proteins and an S-layer lattice, integrated into the cytoplasmic membrane, (b) Using this supramolecular construction principle, biomimetic membranes can be generated. The cytoplasmic membrane is replaced by a phospholipid or tetraether hpid monolayer, and bacterial S-layer proteins are crystallized to form a coherent lattice on the lipid film. Subsequently, integral model membrane proteins can be reconstituted in the composite S-layer-supported lipid membrane. (Modified from Ref. 124.)... 

Another important area of future development concerns copying the supramolecular principle of cell envelopes of archaea, which have evolved in the most extreme and hostile ecosystems. This biomimetic approach is expected to lead to new technologies for stabilizing fnnctional lipid membranes and their nse at the mesoscopic and macroscopic scales [200]. Along the same line, liposomes coated with S-layer lattices resemble archaeal cell envelopes or virns envelopes. Since liposomes have a broad application potential, particu-... 

As an intermediate between solid supported layers and the inherent dynamic and nanostructured properties of phospholipid vesicle supports, silica and especially mesoporous silica nanoparticles may provide interesting platforms for dynamic bilayers. Previous studies have shown that stable bilayers can form on both amorphous [102] or functional silica [103, 104] and mesoporous nanoparticles [105] or membranes [106]. This type of biomimetic carrier has great potential as a type of trackable stabilized membrane capable of displaying cellular targeting elements in a close to natural configuration. 

Figure 2.9a shows the lipid molecule DMPC. Two layers contacted via the hydrophobic tails lead to spontaneous formation of a double-layer biomimetic membrane that can be transferred to a single-crystal ultraplanar electrochemical Au(lll) surface. The hydrophilic head groups contact the electrode surface via an intermediate water film. Due to the structurally very well-defined assembly, not only AFM and in situ STM but also neutron reflectivity. X-ray diffraction, and infrared reflection absorption spectroscopy (IRRAS) have been employed to support the direct visual in situ STM. Electrochemically controlled structural changes, phase transitions, and the effects of the common membrane component cholesterol (Figure 2.9b) and peptide drugs have been investigated in this way. 

With only a few exceptions, metal-supported biomimetic membranes consist of a more or less complex architecture that includes a lipid bilayer. In order of increasing complexity, they can be classified into solid-supported bilayer lipid membranes (sBLMs), tethered bilayer lipid membranes (tBLMs), polymer-cushioned bilayer lipid membranes (pBLMs), S-layer stabilized bilayer lipid membranes (ssBLMs), and protein-tethered bilayer hpid membranes (ptBLMs). 

The schematics of the preparation protocol for plasma-polymer-tethered bilayers are given in Fig. 13 mixed vesicles containing a negative and a zwitterionic lipid were fused in a Ca2+ containing buffer solution onto decylamine derivatized MAH-PP films. The MAH-PP layer appears to form a sub-membrane architecture, which exhibits some of the properties required for biomimetic membrane supports by acting as a polyelectrolyte cushion for the fluid bilayer membrane. 

The biomimetic character of the clay-supported lipid interface is also beneficial for the immobilization of certain proteins, especially membrane-bound enzymes. The catalytic activity of such enzymes is very sensitive to the accommodating environment and easily compromised by protein structure deformations. It could be shown in electrochemical assays that, for instance, cholesterol oxidase (COx) maintained its catalytic activity when supported on sepiolite offering a bUayer lipid membrane [102]. However, the activity of COx was largely diminished after immobilization on sepiolite hybrids displaying cetyltrimethylammonium or hybrid lipid/octyl-galactoside layers, underlining the importance of biomimetic interfaces such as the bilayer lipid membrane for good stabilization of such enzymes. This... 

Hence, at present, the main applications remain in the research environment. LB films are particularly useful for the reconstitution of natural cell membranes on planar substrates for various kinds of biologically oriented investigation. Although most reported work has used pure, synthetic lipids, the technique can equally well be used with natural cell membrane extracts containing proteins (J.J. Ramsden and V. Mirsky, unpublished observations). Langmuir monolayers have been used to create biomimetic structures (see, e.g., Nandi and VolLhardt s review of mono-layers made from chiral molecules ). 

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