Lipid bilayers models

Strong support for the lipid bilayer model comes from the preparation of another type of artificial mem-... 

Prenner EJ, Lewis RNAH, McElhaney RN. The interaction of the antimicrobial peptide gramicidin S with lipid bilayer model and biological membranes. Biochim. Biophys. Acta 1999 1462 201-221. Papahadjonponlos D, Moscarello M, Eylar EH, Isaac T. Effects of proteins on thermotropic phase transitions of phospholipid membranes. Biochim. Biophys. Acta 1975 401 317-335. 

Lipid bilayer. Model for the structure of the cell membrane based on the interaction between the hydrophobic regions of phospholipids. 

In this case it is absolutely necessary to embed the protein in a coherent lipid bilayer model, along with all the necessary water and ions or counter ions. This results in a very large system and the atoms belonging to the environment of the protein account for six to seven times the atoms of the protein (remember that computational times are proportional to the square of the number of atoms). The PBC convention is used throughout, allowing in fact the creation of a quasi-infinite multilayered system (Figme 9.14). 

Figure 8.12 The lipid bilayer model. Circles represent the polar portion of phosphoglycerides. The hydrocarbon "tails" are within the interior of the bilayer.

Figure 4.46 Lipid bilayer model of LDL structure. From Lewis [313]. Lewis describes the model in this way A protein network is envisaged, with icosahedral symmetry it is suggested that there are 60 such units, existing as trimers. Instead of the conventional view of a protein>coated molecule with a lipid core, it was proposed that the lipids are org-aized into a spherical bilayer. The two lipid layers are mirror images, the non-polar regions of their main constituents, phospholipid and cholesteryl ester, oriented towards each other. At the outer surface of the outer layer and the inner surface of the inner layer are situated the polar groups of the phospholipids and the cholesterol side chains these regions of the major constituents are thus adjacent to the protein units on the surface and to a presumptive protein component at the centre of the particle. ...

Mannock, D.A., Lewis, R.N.A.H., McMullen, T.P.W., and McElhaney, R.N. (2010) The effect of variations in phospholipid and sterol structure on the nature of lipid-sterol interactions in lipid bilayer model membranes. Chem. Phys. Lipids, 163, 403—448. 

The most instructive example of studying water accessibility with spin-label ESEEM is afforded by lipid-bilayer model biomembranes. Phospholipids are spin labelled at specific positions down their hydrocarbon chains to map out the profile of water permeation into the membrane. Water penetration is detected as the H-ESEEM amplitudes from D2O in which the lipid membranes are dispersed. 

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