Bilayer random coil

Cationic lipids can destabilize a cellular membrane because of its intrinsic detergent property. Therefore, destabilization of endosomal and/or lysosomal membrane may be a contribution from the cationic lipids itself In the same context, it was shown that the cationic lipid/DOPE or cationic lipid/cholesterol liposome formulation exhibit surface anisotropies in terms of increased liposomal surface pH (161,162). The surface pH of the liposomal formulations exhibits at least two pH units higher than the pH of the solution at which they are made. Therefore, a liposomal solution made at physiological pH may in reality exhibit a surface pH > 9, which is detrimental for both the stability of endosome and activity of lysosomal enzymes. Endosomal disruptions were also done with fusogenic peptides, which promote pH-dependent fusion of small liposomes when associated with lipid bilayer. When these peptides were co-delivered with lipid/DNA complex, they imparted formidable endosomal disruption by changing its usual random coil conformation into amphipathic a-helix conformation at lower pH, resulting in consequent cytoplasmic delivery of DNA (163). 

Many inorganic hydrophobic colloids are polycrystalline particles having irregular shapes and, as a first approximation, such particles are often treated as having a regular shape, for example, a sphere, cylinder, and the like. Solid particles are essentially nondeformable. Most reversible colloids have a more or less flexible three-dimensional structure as a result of thermal motion their shape may vary in time. Examples are the (random) coil structure of a dissolved polymer molecule and the undulation of the lamellar structure of phospholipid bilayers. 

Thickness. The thickness of polymersome bilayers is several times greater than that of typical phospholipid bilayers in natural membranes. Lipid bilayers have a hydrophobic core thickness that is in a very narrow range of rf 3-4 nm to be compatible with integral membrane proteins. For self-assembled bilayers of PEE-PEO vesicles, the hydrophobic core thickness increases with increasing molecular weight from d 8-21 nm (see Fig. 18) to more than 100 nm (53,151-153). The observed d scaling is t5q)ical for random coil polymers and agrees... 

In Fundamentals F.1 and Chapter 2 we saw that proteins and biological membranes can exist in ordered structures stabilized by a variety of molecular interactions, such as hydrogen bonds and hydrophobic interactions. However, when certain conditions are changed, the helical and sheet structures of a polypeptide chain may collapse into a random coil and the hydrocarbon chains in the interior of bilayer membranes may become more or less flexible. These structural changes maybe regarded as phase transitions in which molecular interactions in compact phases are disrupted at characteristic transition temperatures to yield phases in which the atoms can move more randomly. 

Since the random-coil model is a good model of bulk n-alkane, it is not so surprising that the present model is successful in reproducing a wide range of the static properties of the lipid bilayer molecular dynamics simulation. 

The urea purified proteins were analysed by Circular Dichroism. C.D. s were carried out in a solvent with a dipole moment proported to represent the internal environment of a lipid bilayer. The spectra (Figure 2) showed a high percentage of a-helix (55-60%), the remainder being mainly random coil, with some 13-sheet configuration. As the dipole moment of the solution increased (with the addition of water) so did the 13-sheet content of the oil-body protein. 

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