Lipids and membranes

2 Lipids and Membranes. Mastoparan X was studied by both high-resolution and solid-state NMR techniques to determine the structure and orientation of MPX when associated with bicelles. Membrane elasticity in the presence of cholesterol and detergents. 

Solid-state NMR line shape, carbonyl chemical shifts and 2D exchange of protein backbone carbonyl nuclei were applied to structural studies of the membrane-bound HN-I fusion peptide. 

In addition to proteins, biomembranes are also a major eomponent of cells. They not only constitute the cell boundary that separates cells from the extracellular milieu, but they are also neeessary for intracellular sub-compartmentalization, encapsulating both intracellular organelles (endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, 

Because of their importance and ubiquity, it is not surprising that large efforts have been made to accurately deseribe membranes using theoretical and computational approaches, and espeeially in order to keep up with the exploding wealth of experimental data available on the subject in the last few decades. Yet, chemical and physical properties of membranes are remarkably different from those of proteins, and modelling attempts 

The physicochemical differences between proteins and membranes originate from their basic constituents. While proteins are composed of amino acids, membranes are made of lipids amphipathic molecules characterized by having a polar head at one extremity and a highly hydrophobic moiety at the other end, typically in the form of hydrocarbon chains, with the two ends usually connected by a small linker (most frequently glycerol or sphingosin). 

Even though the chemistry of lipids can be as rich as one can imagine, thanks to the numerous combinatorial ways in which polar heads and acyl chains can combine, the most glaring property of lipids is their capability of self-assembly into membranes, usually in a bilayer conformation where two lipid monolayers come into contact through their hydrophobic moieties, thus preventing the passage of both water and polar solutes across the bilayer. 

Lipid bilayers are only few nanometres thick, but they can stably span macroscopic lateral scales (Fig. 11). Considering that each lipid occupies a surface area of approximately 0.6-0.7nm and consists of approximately 40-50 heavy atoms, it is evident that an atomistic description of an entire membrane would be rather prohibitive from a computational point of view. 

Satisfied humans depend on fats in their food in order to experience a smooth mouthfeel and the rich aroma of fat-dissolved food. This feeling is, however, paid for with junk calories in the food. Chemists can help to get rid of digestible fat without disturbing the pleasure derived from both mouthfeel and aroma. 

Organic chemists rely on amphiphilic lipids to build up membranes in water—the only organic reaction medium of nature. Biological molecular machinery is based on lipid membrane potentials. Artificial models so far do not work like cell membranes in vectorial transport and charge separation chains, but they look good under the electron microscope. 

Solid state NMR studies of the effects of cholesterol on the acyl chain dynamics of magnetically aligned phospholipid bilayers have been reported. The results suggest that cholesterol is incorporated into the bicelle discs. The order parameters were extracted directly from the quadrupolar splittings, and indicated an overall degree of ordering of the acyl chains of the phospholipids in the presence of cholesterol. 

The effects of cholesterol on magnetically aligned phospholipid bilayers (bi-celles) have also been studied using both solid state NMR spectroscopy and EPR spectroscopy. It was shown that EPR spectroscopy and NMR spectroscopy exhibit different degrees of sensitivity in detecting the phosphohpid molecular motions in the membrane. 

Structural changes in the lipid bilayer upon insertion of the transmembrane domain of the membrane-bound protein phospholamban (PLB) were studied using P and solid state NMR. Phospholamban is a 52-amino acid integral membrane protein that regulates the flow of Ca ions in cardiac muscle cells. Solid state NMR experiments were carried out to study the behavior of lipid bilayers in the presence of the hydrophobic PLB at different temperatures. P NMR was used to study the different phases formed by phospholipid membranes. Simulations of the P NMR spectra were carried out to reveal the formation of different vesicle sizes upon PLB insertion. Molecular order parameters were calculated by performing solid state NMR studies on deuterated phospholipid bilayers. 

Peptide-related alterations of membrane-associated water has been investigated using solid state and P NMR of phosphatidylcholine membranes at 

Solid state NMR investigations of exchange labelled oriented purple membranes at different hydration levels have been reported. Four populations were resolved. Deuterons that have exchanged with amide protons of the protein exhibited a broad spectral line shape ( 150 kHz). A broadened signal of deuterons tightly associated with protein and lipid was also detected at low hydration, as well as two additional water populations that were present when 

Different types of mimetic systems of biological membranes including vesicles (spherical phospholipid bilayers), LB monolayers, hybrid bilayers (HBLs) and tethered lipid bilayers were used in SERS investigations. LB films are monomolecular films that can be fabricated from amphiphiles at the water-air interface and transferred to a SERS solid substrate (such as island film). For SERS studies, the target molecule was treated as a dopant in a monolayer matrix formed for example by arachidic acid or phospholipids. Aroca and co-workers applied the LB technique to detect SERRS signal firom a variety of chromophores such as several perylene derivatives and RH6G even in SM level in some cases (Aroca 2006). HBLs are monolayers of phospholipids incorporated into SAM of long-chain thiols such as 

16 SERS study of lipids. A SERS spectra of (a) HBL formed with DMPC, (b) HBL framed with DMPC incubated with d-DMPC vesicles and (c) a HBL formed with d-DMPC. The loifics ratio for the three dilfcaent systems is shown in inset. B A plot of Ich Ics versus time and a scheme of the plausible changes in the HBL composition (adapted with permission fiom Kundu et aL 2009b. Copyright 2009 The Royal Society of Chemistry) 

SERS has been employed to monitor incorporation of some molecules, such as medicament pirambicin (Heywang et al. 1996) or photosensitizer hypericin (Lajos et al. 2009) inside the membranes. In order to interface lipid bilayers with solid substrates, many groups employ tethered lipid bilayers. In these systems, a lipid 

Garren, J.D. Driskell, R.A. Tripp, Y. Zhao, Label-free detection of micro-RNA 

Surface-Enhanced Vibrational Spectroscopy (John Wiley Sons, Chichester, 2006) E. Bailo, V. Deckert, Tip-enhanced Raman spectroscopy of single RNA strands towards a novel 

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Vance, D. E., and Vance, J. E. (eds.), 1985. Biochemistry of Lipids and Membranes. Menlo Park, CA. Benjamin-Cnmmings. 

Schulz, H. (1985). Oxidation of fatty acids. In Biochemistry of Lipids and Membranes (Vance, D.E. 

The dissociation rate of heme from methemoglobin and consequent formation of the heme-hemopexin complex is facile at 37°C, and the presence of small amounts of H2O2 (even below levels obtained from the respiratory burst of neutrophils) dramatically increases heme dissociation from oxyhemoglobin (55). The binding of heme by hemopexin prevents the oxidation of lipoprotein (50,55,56) and lipid and membrane damage (57-59). 

Quinn, P. J., and Cherry, R. J., eds. (1992) Structural and Dynamic Properties of Lipids and Membranes, Portland Press, London Disalvo, E. A., and Simon, S. A., eds. (1995) Permeability and Stability of Lipid Bilayers, CRC Press, Boca Raton, Florida Jacobson, K., Sheets, E. D., and Simson, R. 

Rogers, R.A., Jack, R.M. and Furlong, S.T. (1993) Lipid and membrane protein transfer from human neutrophils to schistosomes is mediated by ligand binding. Journal of Cell Science 106 (Pt 2), 485-M91. 

Our studies of the bacterial enzymes utilized in peptidoglycan biosynthesis required an ample supply of both lipid I and lipid II. Isolation of these precursors from bacterial sources presented significant challenges. First, each of these intermediates is present in very low copy numbers. For example, in E. coli, the copy numbers for lipid I and lipid II are estimated to be approximately 700 and 1000-2000 molecules per cell, respectively.9 Second, separation of miniscule amounts of the cell wall precursors from the comparatively large amounts of cellular lipid and membrane components is technically challenging and further compromises the ability to isolate sufficient quantities of the enzyme substrates to enable detailed mechanistic studies.10... 

E. Interaction with Lipids and Membranes Involvement in Membrane Trafficking... 

Shearman GC, Ces O, Templer RH et al (2006) Inverse lyotropic phases of lipids and membrane curvature. J Phys Condens Matter 18 S1105-S1124... 

Luzzati, V., Gulik, A., Gulik-Krzywicki, T., Tardieu, A. Lipid polymorphism revisited Structural aspects and biological implications. Lipids and Membranes Past, Present, and Future. Elsevier, Amsterdam (1986), pp. 137-151. 

Figure 9.24 The fluid-mosaic model of plasma membrane. Phospholipids with darkened heads are on the cytosol side of the bilayer, and the lipids with unfilled heads are on the outer surface. In intrinsic proteins one or more a-helical segments are in contact with the hydrophobic environment of the bilayer. They usually have hydrophobic amino acid side chains. Carbohydrate is indicated by hexagons. The membrane potential (negative inside) is indicated by AV. (Reproduced by permission from Vance DE, Vance JE. Biochemistry of Lipids and Membranes. Menlo Park Benjamin/Cummings, 1985, p. 26.)...

Harold FM. The Vital Force A Study of Bioenergetics. New York WH Freeman, 1986. Vance DE, Vance JE. Biochemistry of Lipids and Membranes. Menlo Park Benjamin-Cummings, 1985. 

The chemistry of phosphate esters and anhydrides is so central to biochemistry that the subject might also be logically discussed in the sections on nucleic acids, lipids and membranes, or intermediary metabolism. However, because of the importance of sugar phosphates and their derivatives in Experiment 12, the subject is presented in this section. The background is important to more than Exper-... 

Hounsell EF. NMR of carbohydrates, lipids and membranes. In Specialist Periodical Reports on NMR, Vol. 34. 2005. The Royal Society of Chemistry, London. 

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