Molecules lipid interactions

We mention a few studies on polar and charged molecule-lipid interactions, as their permeation involves defect and pore formation, which involves lipid-lipid interactions. A detailed examination of small molecule-lipid interactions is beyond the scope of this chapter [74], We have shown that a large component of the free energy of small polar or charged molecule partitioning into lipid bilayers is due to the cost of forming a defect [75]. 

As mentioned earlier, fullerene molecules can destroy the virions, but do not affect living cells. It is possible to suppose that the differences of the structures of virion envelope and cell membrane are the main reason for this phenomenon the outer side of virion envelope is enriched with protein molecules, whereas the outer side of cell membranes is more lipophylic. On the one hand, fullerene molecules can interact with proteins (Belgorodsky et al., 2006), and on the other hand, their penetration into a lipid bilayer does not destroy them (Ikeda et al., 2005 Piotrovsky, 2006). So it is not unlikely that the difference in the structure of outer side is the main driving force of the observed differences in the response of virions and cells in the presence of C60. 

Fig.3 A migrating zone of solute molecules (spots) interacting with lipid bilayers (rings) in a chromatographic or electrophoretic separation system. The free solute molecules move (arrows) relative to the liposomes or vesicles in a flow of eluent or in an electric field. The solute molecules may either partition into the membranes and diffuse between the external and internal aqueous compartments of the structures as depicted, or interact with the external surface of the membranes and stay outside.

Figure 11. (a) The chemical structure of a 24-membered macrocyclic molecule composed of alternating D- and L-amino acids, cyclo(Gln-(D-Leu-Trp)4-D-Leu 7. (b)A self-assembled tubular structure spanned across the bilayer lipid membrane. Flat ring-shaped units in the antiparallel configuration stack to form a tubular structure through extensive inter subunit hydrogen bonding and peptide side chain-lipid interactions. ... 

In the larger peptide antibiotic compounds comprising the class of lantibiotics, the shape of the molecule is determined by several cyclic peptides, including two annulated peptide rings, present within one molecule, giving the lantibiotic a unique way to interact with the target molecule lipid II and subsequent pore-forming capabilities in phospholipid membranes [2]. 

Polar molecules can interact weakly with other polar molecules through the same mechanism outlined above. As neither pole of the molecule is particularly strongly charged this type of interaction is necessarily weak. Nevertheless, it may play a part in the orientation of polar hydrocarbons that aggregate to form micelles and lipid bilayers, the forerunners of today s biological cells. 

In an aqueous medium, the hydrophobic interaction plays a very important role. It is the major driving force for hydrophobic molecules to aggregate in an aqueous medium, as seen in the formation of a cell membrane from lipid-based components. The hydrophobic interaction is not, as its name may suggest, an interaction between hydrophobic molecules. This interaction is related to the hydration structure present around hydrophobic molecules. Water molecules form structured hydration layers that are not entropically advantageous. It is believed that hydrophobic substances aggregate to minimize the number water molecules involved in hydration layers. However, the mechanism and nature of the hydrophobic interaction is not that clear. Unusual characteristics, such as incredible interaction distances, have been reported for the hydrophobic interaction, and the fundamentals of hydrophobic interaction are still under debate even today. 

A comparative study of different poliovirus capsid structures revealed a hydrophobic pocket that contained sites for cellular lipid interaction (Hogle et al, 1985 Filman et al, 1989). This lipid component, which is termed the pocket factor, may be sphingosine. Amino acids that modulate temperature sensitivity of poliovirus infectivity map to the interfaces between capsid protomers and are adjacent to the site of lipid binding. A similar lipid molecule appears to be present in some but not all... 

The structure of this water-selective membrane pore protein (Fig. 3a and 3b) represents the highest resolution stmcture obtained from electron crystallography to date (53). Data were obtained for Aquaporin-O in double-layered 2-D crystals, and its staggering 1.9-A resolution clearly reveals water molecules within the pore. The data also reveal associated lipids, allowing key protein-lipid interactions to be modeled. 

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