Lipids molecular architecture

Chain models capture the basic elements of the amphiphilic behaviour by retaining details of the molecular architecture. Ben-Shaul et aJ [ ] and others [ ] explored the organization of tlie hydrophobic portion in lipid micelles and bilayers by retaining the confonuational statistics of the hydrocarbon tail withm the RIS (rotational isomeric state) model [4, 5] while representing the hydrophilic/liydrophobic mterface merely by an... 

Myelin in situ has a water content of about 40%. The dry mass of both CNS and PNS myelin is characterized by a high proportion of lipid (70-85%) and, consequently, a low proportion of protein (15-30%). By comparison, most biological membranes have a higher ratio of proteins to lipids. The currently accepted view of membrane structure is that of a lipid bilayer with integral membrane proteins embedded in the bilayer and other extrinsic proteins attached to one surface or the other by weaker linkages. Proteins and lipids are asymmetrically distributed in this bilayer, with only partial asymmetry of the lipids. The proposed molecular architecture of the layered membranes of compact myelin fits such a concept (Fig. 4-11). Models of compact myelin are based on data from electron microscopy, immunostaining, X-ray diffraction, surface probes studies, structural abnormalities in mutant mice, correlations between structure and composition in various species, and predictions of protein structure from sequencing information [4]. 

Yu YC, Tirrell M, Fields GB. Minimal lipidation stabilizes protein-like molecular architecture. J Am. Chem. Soc. 1998 120 9979-9987. 

Firestone et al. investigated the relationship between the molecular architecture of a series ofpoly(ethyleneoxide)-b-poly(propylene oxide) (PEO—PPO) di- and triblock copolymers and the nature of their interactions with lipid bilayers [213], The number of repeat units in the hydrophobic PPO block has been found to be a critical determinant for the polymer-lipid bilayer association. Further studies showed that temperature, polymer architecture and concentration also control the mode of interaction of PEO—PPO—PEO copolymers with lipid bilayers. Increasing either the number of repeat units in the PEO block or the polymer concentration promotes a greater degree of structural ordering [197],... 

The terms Y -shaped [109], tripodal , 1,1-double-tailed or peg-shaped [110] describe the molecular geometry of this type of amphiphile. At the hydrophilic head two hydrophobic tails are joined close together or even by a common link to the headgroup. Very famous examples for this molecular architecture are the biologically active phospholipids and sphingolipids [111]. Lipids occur in all biological cells and have common solubility properties generally they are water-insoluble, amphiphilic molecules... 

Electrochemistry may also be used to probe the interactions between ferrocifens and nonpolar molecular architectures, with respect to the hydrophobic architectures/barriers that compose ceU membranes as well as lipidic cargoes/vectors (e.g., liposomes) using model systems consisting of glassy carbon electrodes modified with a planar bilayer of 1,2-dimyristoyl-OT-glycero-3-phosphocholine (DMPC) (Fig. 47.20) [56]. 

FIGURE 1 Structure of a peptide-amphiphile with triple-helical protein-like molecular architecture. Long-chain diaUQ l ester lipid tails (top left) are connected to linear peptide... 

The aspect missing so far concerns the bilayer feature of the membrane. It is not possible to describe the membrane just as a structureless two-dimensional surface. As one key signature of its molecular architecture, the bilayer architecture must be retained in the model. The two monolayers are tightly coupled but the exchange of lipid molecules between them is slow compared to the experimental time-scale of these observations. Therefore, the numbers iV and iV" of molecules in the outer and inner monolayer, respectively, are conserved. The number difference — N leads to the prefered area difference AAq = (A+ — N )aQ between the two layers. Here, gq is the equilibrium area per lipid molecule. The actual area difference, AA = A —A, can be expressed as an integral over the closed surface ns AA =2D dAH where D is the distance between the neutral surfaces of the two monolayers, i.e. roughly half the bilayer thickness. Deviations of the true area from the prefered area cost energy [15] ... 

It would appear that among the sphingoglycolipids we have a family of lipids differing widely in polarity and in tendencies toward micelle formation (Hakamori, 1965 Howard and Burton, 1964). It seems likely that such compounds will have as yet unforeseen roles in the molecular architecture of the membranes in which they occur. 

Nabika, H., Sasaki, A.,Takimoto, B., Sawai, Y, He, S. and Murakoshi, K. (2005) Controlling molecular diffusion in selfspreading lipid bilayer using periodic array of ultra-small metallic architecture on solid surface. J. Am. Chem. Soc., 127, 16786-16787. 

Although varying considerably in molecular size, any GPCR polypeptide sequence contains seven hydrophobic a-helices that span the lipid bilayer and dictate the typical macromolecule architecture. Seven transmembrane domains bundled up to form a polar internal tunnel and expose the N-terminus and three interconnecting loops, to the exterior, and the C-terminus with a matching number of loops, to the interior of the cell [1-3]. This structural information was recently confirmed by the resolution of the crystal structure of rhodopsin [4,5]. 

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