Membrane lipid bilayers model membranes

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. 

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. 

Fig. 4. (A) The side view of the LHC-II monomer in the membrane (lipid bilayer). The chlorophyll molecules are oriented nearly perpendicular to the membrane plane (the phytyl chains are omitted for clarity). Two lutein molecules form an internal X-shaped brace. (B) A sketch of the amino-acid sequence of the LHC-II polypeptide and a listing of the known Chl-residue ligation. White letters inside black circles indicate amino-acid ligands to the chlorophylls [also see legend on the right side of (B)]. Note that the model in (B) is rotated 90° with respect to that in (A) about an axis normal to the membrane. Figure source (A) Kuhibrandt, Wang and Fujiyoshi (1994) Atomic model of plant light-harvesting complex by electron crystallography. Nature 367 618 and 620.

In order to elucidate the physicochemical properties of such a biological membrane interface, several model membrane systems (lipid monolayer, lipid bilayers, and protein-incorporated lipid model membrane systems) which mimic biological membrane interfaces have also been studied.In particular, many properties at the membrane surface are intimately related to the electrical potential originating from the fixed charge or electrical polarization of the membrane constitutents. 

Fluid-mosaic model of a biological membrane, showing the lipid bilayer with membrane proteins oriented on the inner and outer surfaces of the membrane, and penetrating the entire thickness of the membrane. 

The vast majority of cation transport model studies have been conducted using crown ethers as ionophores and bulk liquid membranes as bilayer models. Much information has been obtained about carrier-mediated transport [1,7] but the mechanism for transport of molecules through biological membranes is predominantly of the channel type [8]. The synthesis of a cation-conducting channel is a daunting task. We felt that a suitable compound would require at least three basic features. First, it must be capable of insertion into a lipid bilayer. Second, it must span the membrane. Third it must have some residue integral to it that would... 

The molecular mechanisms responsible for these properties have not been elucidated (Wenner and Dougherty, 1971) nor has it been established that similar mechanisms are operative in membranes. However, the sheer multiplicity of corresponding properties in modified lipid bilayers and membranes is at least suggestive that the Danielli model, which describes a protein-modified lipid bilayer, could be representative of both structures. 

ESEEM amplitudes of spin-labelled molecules can depend on the freezing protocol, and this can cause non-reproducibility in the data, as was shown for spin-labelled lipids in model membranes. This effect can be explained by exclusion of the spin-labelled lipids from the bilayer, and by the presence of U-shaped lipid conformations, which can occur during freezing of the sample. ... 

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. 

Biological membranes provide the essential barrier between cells and the organelles of which cells are composed. Cellular membranes are complicated extensive biomolecular sheetlike structures, mostly fonned by lipid molecules held together by cooperative nonco-valent interactions. A membrane is not a static structure, but rather a complex dynamical two-dimensional liquid crystalline fluid mosaic of oriented proteins and lipids. A number of experimental approaches can be used to investigate and characterize biological membranes. However, the complexity of membranes is such that experimental data remain very difficult to interpret at the microscopic level. In recent years, computational studies of membranes based on detailed atomic models, as summarized in Chapter 21, have greatly increased the ability to interpret experimental data, yielding a much-improved picture of the structure and dynamics of lipid bilayers and the relationship of those properties to membrane function [21]. 

Baumgartner and coworkers [145,146] study lipid-protein interactions in lipid bilayers. The lipids are modeled as chains of hard spheres with heads tethered to two virtual surfaces, representing the two sides of the bilayer. Within this model, Baumgartner [145] has investigated the influence of membrane curvature on the conformations of a long embedded chain (a protein ). He predicts that the protein spontaneously localizes on the inner side of the membrane, due to the larger fluctuations of lipid density there. Sintes and Baumgartner [146] have calculated the lipid-mediated interactions between cylindrical inclusions ( proteins ). Apart from the... 

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