Bilayers interactions

The artificial lipid bilayer is often prepared via the vesicle-fusion method [8]. In the vesicle fusion process, immersing a solid substrate in a vesicle dispersion solution induces adsorption and rupture of the vesicles on the substrate, which yields a planar and continuous lipid bilayer structure (Figure 13.1) [9]. The Langmuir-Blodgett transfer process is also a useful method [10]. These artificial lipid bilayers can support various biomolecules [11-16]. However, we have to take care because some transmembrane proteins incorporated in these artificial lipid bilayers interact directly with the substrate surface due to a lack of sufficient space between the bilayer and the substrate. This alters the native properties of the proteins and prohibits free diffusion in the lipid bilayer [17[. To avoid this undesirable situation, polymer-supported bilayers [7, 18, 19] or tethered bilayers [20, 21] are used. 

Farsad K, Ringstad N, Takei K, Floyd SR, Rose K, De Camilli P (2001) Generation of high curvature membranes mediated by direct endophilin bilayer interactions. J. Cell Biol. 155 193-200. 

E. A. Haigh, K. R. Thulborn, and W. H. Sawyer, Comparison of fluorescence energy transfer and quenching methods to establish the position and orientation of components within the transverse plane of the lipid bilayer. Application to the gramicidin A-bilayer interaction, Biochemistry 18, 3525-3532 (1979). 

Another example of ACE analyses of solute-bilayer interactions was described by Roberts et al. (50), who observed retardation of riboflavin by liposomes. Analyses technically similar to liposomal ACE have been performed with mixed bile salt/phosphatidylcholine/fatty acid micelles (95). The partitioning of basic and acidic drugs depended on the acid-base properties of the drug and on the shape and charge of the mixed micelles. 

Ogg, D., Elleby, B., Norstrom, C., Stelans-son, K., Abrahmsen, L., Oppermann, U., Svensson, S. (2005) The crystal structure of guinea pig llfl-hydroxysteroid dehydrogenase type 1 provides a model for enzyme-lipid bilayer interactions. J Biol Chem 280, 3789-3794. 

Between bilayers immobilized onto substrates,55 bilayer-bilayer interaction measurements also sense interactions involving the substrate. After compensation for these features, measurements on all three systems pleasingly agree.56... 

For measurements between crossed mica cylinders coated with phospholipid bilayers in water, see J. Marra andj. Israelachvili, "Direct measurements of forces between phosphatidylcholine and phosphatidylethanolamine bilayers in aqueous electrolyte solutions," Biochemistry, 24, 4608-18 (1985). Interpretation in terms of expressions for layered structures and the connection to direct measurements between bilayers in water is given in V. A. Parsegian, "Reconciliation of van der Waals force measurements between phosphatidylcholine bilayers in water and between bilayer-coated mica surfaces," Langmuir, 9, 3625-8 (1993). The bilayer-bilayer interactions are reported in E. A. Evans and M. Metcalfe, "Free energy potential for aggregation of giant, neutral lipid bilayer vesicles by van der Waals attraction," Biophys. J., 46, 423-6 (1984). 

The role of thermal fluctuations for membranes interacting via arbitrary potentials, which constitutes a problem of general interest, is however still unsolved. Earlier treatments G-7 coupled the fluctuations and the interaction potential and revealed that the fluctuation pressure has a different functional dependence on the intermembrane separation than that predicted by Helfrich for rigid-wall interactions. The calculations were refined later by using variational methods.3 8 The first of them employed a symmetric functional form for the distribution of the membrane positions as the solution of a diffusion equation in an infinite well.3 However, recent Monte Carlo simulations of stacks of lipid bilayers interacting via realistic potentials indicated that the distribution of the intermembrane distances is asymmetric 9 the root-mean-square fluctuations obtained from experiment were also shown to be in disagreement with this theory.10... 

When two fluctuating bilayers interact, the intermembrane distance distribution is still given by eq 5, since the interaction depends only on the distance z between the bilayers. For an arbitrary interaction (per unit area) U(z) and a constant applied pressure p, the Boltzmann distribution of distances between the small independent surfaces of area S0 can be calculated using the enthalpy (per unit area) H(z) = U(z) + pz instead of the energy... 

Line shape analysis of the static 31P NMR spectra and its corresponding CSA values have been successfully used to study the perturbation effect induced by proteins. 31P data for PLs bilayers interacting with antimicrobial peptide (AMP) magainin-2, aurein-3,3, incorporated into structures of supramolecular lipid assemblies such as toroidal pores and thinned bilayers have been reported.90 Various types of PL systems (l-palmitoyl-d3i-2-oleoyl-s -glycero-3-phosphotidylcholine... 

Crommelin, D. J. A., and Van Bloois, L. (1983), Preparation and characterization of doxorubicin containing liposomes. Part 2. Loading capacity, long-term stability and doxorubicin bilayer interaction mechanism, Int. I. Pharm., 17,135-144. 

Hence we conclude that a mesoscopic description for the size of an onion is quantitatively possible and that the mesoscopic determinants are bilayer flexibility and bilayer interaction. 

Having established that bilayer flexibility and bilayer interaction are the mesoscopic determinants, the next question is whether these determinants can be coupled to molecular parameters. In fact, this has been done to quite some extent. In general, bilayer flexibility can be shown (both experimentally as well as theoretically by simulation methods) to be directly related to bilayer thickness, lateral interaction between heads and tails of the surfactants, type of head group (ethoxylate, sugar, etc.), type of tail (saturated, unsaturated) and specific molecular mixes (e.g. SDS with or without pen-tanol). The bilayer interaction is known to be related to characteristics such as classical electrostatics. Van der Waals, Helfrich undulation forces (stemming from shape fluctuations), steric hindrance, number, density of bilayers, ionic strength, and type of salt. Two examples will be dicussed. 

J. H. Hurley and J. A. Grobler. 1997. Protein kinase C and phospholipase C Bilayer interactions and regulation Curr. 

Hendrich et al. [155] investigated the mechanism of incorporation of phe-nothiazines in the membrane bilayer lipids. They studied the influence of a particular phenothiazine derivative, TFZ, on the thermal properties of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylethanolamine by microcalorimetry. The main phase transition of both lipids was affected by this drug, depending on its concentration. The results suggest that TFZ was probably incorporated into both dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylethanolamine bilayers. The phase separation was presumably induced by the different modes of the drug-bilayer interactions of protonated and unprotonated forms of TFZ. Only phosphatidylcholine, which possesses polar heads less densely packed in bilayers than phosphatidylethanolamine ones, was able to distinguish between the different protonated forms of TFZ. 

Pan, J., Tristram-Nagle, S., Kucerka, N., and Nagle, J.F. (2008) Temperature dependence of structure, bending rigidity, and bilayer interactions of dioleoylphosphatidylcholine bilayers. Biophysical Journal, 94 (1), 117-124. 

The main stabilizing feature of biological membranes is hydrophobic interactions among the molecules in the lipid bilayer. The phospholipids in the lipid bilayer orient themselves so that their polar head groups interact with water. Proteins in the lipid bilayer interact favorably in their hydrophobic milieu because they typically have hydrophobic amino acid residues on their outer surfaces. 

How do proteins and the lipid bilayer interact with each other in membranes ... 

---