Phospholipid acyl chain conformational

The quantitative determination of phospholipid acyl chain conformational disorder in hydrated systems of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamlne (DPPE), mixtures containing DPPC and cholesterol, and mixtures of DPPC and Gramicidin D has been made using FT-IR. The... 

An additional example for the usefulness of IR spectroscopy in studying drug interactions with phospholipid vesicles is the quantitative determination of acyl chain conformation in gramicidin-DPPC mixtures [63]. The technique provides a quantitative measure of the extent to which membrane-spanning peptides induce disorder of phospholipid gel phases and order in liquid crystalline phases. 

The last group of amphiphiles contains sterols that are present in the membranes of cells. The most popular among them is cholesterol (Choi), which can be easily incorporated in lipid bilayers, increasing their rigidity and making them less permeable, due to the interactions taking place with phospholipids in lipid membranes which result in modification of the lipid acyl-chain conformation. 

IRRAS has become an important tool for studying Langmuir monolayers and LB films. Much work has been done, in particular on the acyl chain conformational order in monolayers of single chain amphiphiles and phospholipids as a function of surface pressure and on the occurrence of phase transitions . Examples of IRRAS studies on LB films can be found Reviews of the applications of IRRAS are given by Dluhy et al. and Mendelsohn et al. ). 

In visual signal transduction, activation proceeds from the receptor, rhodopsin, to the effector, phosphodiesterase (PDE), via the visual G protein, Gp Each Mil sequentially binds and activates up to 100 Gj, thus MII-Gj binding initiates the first stage of signal amplification in the visual pathway. Litman et al. (2001) have studied the phospholipid acyl chain dependence of the kinetics of formation of both the Mil conformation and the... 

RA. Quantitative determination of conformational disorder in the 38. acyl chains of phospholipid bilayers by infrared spectroscopy. Biochemistry 1989 28 8934-8939. 

A major effect of cholesterol on the conformation of apoE was revealed by comparing the conformation on DMPC discs, on HDLc, and on spherical artificial microemulsion particles by circular dichroism (Mims et ai, 1990). Conformational differences of apoE on different types of particles also were demonstrated using NMR to probe lysyl microenvironments. When the apoE lysyl residues were labeled by reductive methylation with [ C]formaldehyde to allow detection, the lysyl microenvironments manifested dramatic differences on a discoidal particle compared to spherical particles (S. Lund-Katz et aL, 1993). On spherical particles, two lysine microenvironments were observed, but on discoidal particles eight peaks were observed (apoE has 12 lysyl residues). These results indicate that apoE structure differs significantly on the two lipid surfaces. In a systematic study of the effect of the particle lipid composition on the conformation of apoE, conformation was shown to be affected by a number of parameters (Mims et ai, 1990). The a-helical content was lower when apoE was bound to a spherical particle compared to a discoidal particle. It was concluded that this probably reflects the different ways in which the amphipathic helices interact with phospholipid on the two particles. With discoidal particles the interaction is primarily with phospholipid acyl side chains, whereas with spherical particles the interaction is with polar phospholipid head groups. In addition, the conformation of apoE was influenced by the diameter of the microemulsion particle and possibly by the order/ disorder of the lipid components. 

Therraodjmamics of phospholipids depend on their molecular structure the conformation and the geometry of the phospholipids polar head, the orientation of the molecular backbone (glycerol in the case of glycerophospholipids) and the acyl-chaiiis orientation. NMR spectroscopy has been used extensively in order to reveal the lipid orientation in membrane structures [20]. NMR experiments have shown that except for phospatidic acid, in all phospholipid crystal structures a part of the sn-2 fatty acyl chain is parallel to the bilaycr surface. In egg phosphatidylcholines for example the averege size of the sn-2 acyl chain is 18 carbons while the sn- fatty acid is 16 carbons long. The final configuration of the two fatty acyl chains extends to the same depth from the bilayer surface and a thermodynamicaly stable conformation of the acyl lipid chains is formed [21]. 

Mitchell DC, Straume M, Litman B J. Role of sn-2-polyunsaturatcd phospholipids and control of membrane receptor conformational equilibrium effects of cholesterol and acyl chain unsaturation on the metarhodopsin I-metarhodopsin II equilibrium. Biochemistry 1992 31 662-670. 

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