Lipids head groups

Size and charge of the lipid head groups and subphase conditions affect the crystallization [122] The orientation of the S-layer lattice is determined by the subphase conditions" [122]... 

Generally, the recrystaUization of S-layer protein into coherent monolayer on phospholipid films was demonstrated to depend on (1) the phase state of the hpid film, (2) the nature of the lipid head group (size, polarity, and charge), and (3) the ionic content and pH of the subphase [122,138] (Table 6). 

A significant change of the lipid head group interactions is observed [123]... 

The lipid head groups are tilted toward the surface normal of the membrane [139,144]... 

Interaction with a lipid bilayer driven by a potential difference and by polar and/or hydrophobic forces between the amino acid side chains of the pardaxin tetramers and the polar membrane lipid head group triggers insertion from a "raft" like structure. 

Many transmembrane proteins that mediate intracellular signaling form complexes with both intra- and extracellular proteins 25 Membrane associations can occur by selective protein binding to lipid head groups 25... 

Figure 5. Profiles across the bilayer of the total lipid density of DPPC, the water density and the densities of certain lipid groups as obtained from MD simulations by Berger et al. [58]. The profiles are found by taking the time average over the last 300 ps of the simulation. The densities for the lipid head-group components are only shown on one side for clarity. The origin of the z-axis is arbitrarily positioned on the left of the bilayer. On the y-axis, the atom density in atoms per nm3 is given. Redrawn from [58] by permission of the Biophysical Society...

Lipid membranes are quite deformable, allowing water and head groups into their interiors when perturbed. A "water defect" is shown in Figure 1C, where water and lipid head groups enter the hydrophobic interior of only one of the bilayer leaflets. Figure ID shows a "water pore," where both leaflets are perturbed. At the molecular level, pore and defect formation are directly related to specific lipid-lipid interactions. It is important to understand the free energy required for pore formation in membranes and the effect of lipid composition on the process. In Section 3 of this chapter, we review recent MD studies of the thermodynamics of pore formation. 

Figure 12.8 Schematic picture of a biomembrane with associated and transmembrane proteins. As with most schematics, some things are over simplified. For example, in reality the lipid head groups (typical diameter 0.6 nm) are very much smaller than the proteins (typical diameter 3-5 nm). In addition, lipid bilayers are flexible and are usually not perfectly planar.

Cytidine triphosphate Diacylglycerols and lipid head groups Bacteria, archaea and eukaryotes ... 

Several other examples of drug-membrane interactions have been reported. Using X-ray diffraction techniques, interactions with tetracyclines [75], pindolol [76], and chlorpromazine [77, 78] have been described. In these studies, it was shown that in the presence of chlorpromazine the bilayer thickness or lipid head group separation in DPPC liposomes is only 30 A, which is about 20 A smaller than two fully extended DPPC molecules. Chlorpromazine produced an interdigitated phase, which is in agreement with the observed effect of chlorpromazine on the shape of erythrocytes. 

Tab. 4.20 Role of lipid head group in partitioning of teniposide into phospholipid mixtures. (Reprinted from Tab. 1 of ref. 79, with permission from Elsevier Science)...

B. The Benson Lipoprotein Subunit Model. Here, the proteins are globular and the membrane is a protein-lipid mixture. The hydrophobic tails of the lipids are embedded in the hydrophobic parts of the proteins. The lipid head groups are exposed to the solvent. There is no lipid bilayer. 

P SS NMR was found to be useful to demonstrate the relationships between peptides, lipid membranes and metal ions.103 104 Such methodology is developed with intention to understand the mechanism of Alzheimer s disease. Disruption of the membrane structure by /1-amyloid in the presence of metal ions suggests the crucial role of such cations as Zn2+ and Cu2+. Metal ions alone have a different impact on the lipid membrane. Zinc induces weak motions on the lipid head-groups, which results in a slight decrease in 31P CSA. Adding the paramagnetic copper ions can cause total disruption of the lipid membrane to form smaller... 

Lipid bilayers have been studied in vesicles of about 500 A diameter. The bilayers can be made of many lipids. The most common lipid is lecithin, phosphatidyl choline (PC). Packing the lipids in the vesicle results in two-thirds of the lipid head groups on the external face about one-third on the internal face. The head group of the lipid PC is phosphocholine -O-POJ-O-CH2-CH2N (013)3 and the head group is studied by P, H, D or C NMR and the long fatty chains by C, H, or D NMR. Conformational studies of the molecules by conventional de-coupling, nuclear Overhauser effects and by Ln(III) probes... 

Each tetramer comprises four closely associated monomeric channels circled by a hydrophobic surface long enough to span the lipid bilayer (Fig. 4). Toward the cytoplasmic and periplasmic surfaces are layers that include side chains of tyrosine and tryptophan that can productively interact with the polar-nonpolar interface in the lipid head-group region as in other integral membrane proteins (Koeppe and Anderson, 1996). These layers are flanked by two outer layers of charged residues, 35 A apart, that result in net positive charge on the cytoplasmic side. 

Phosphorylated myo-inositol is an important moiety in biochemistry as the basis for signal transduction pathways in eukaryotes. Inositol also occurs in bacteria and archaea, not as part of a signaling pathway, but with diverse and unique uses. wvo-Inositol occurs as part of mycothiol, a molecule comparable to glutathione in mycobacteria, as part of an unusual osmolyte in hyperther-mophiles [e.g., di-myo-inositol-1,1 -phosphate (DIP)], and as the lipid head-group anchor for a series of glycosylated lipids in mycobacteria that are critical in the interaction of pathogenic mycobacteria with mammalian cells. 

The chemistry of the lipid head group helps to explain the ubiquitous nature of these polar lipids. Sugar phosphates are the most fundamental structures in biology. They provide the backbone of DNA and RNA and are the building... 

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