Lipid diffusion lateral

The authors reported that the hydrophobic peptide had little influence on the lipid structure, as lipid lateral diffusion rates, lipid conformations, and head group orientations were identical to a neat bilayer. The distance distribution of the phospholipid atoms surrounding the peptide was rather broad, pointing to the absence of special interactions between the peptide and the surrounding phospholipids. 

Oradd, G., and G. Lindblom (2004) NMR Studies of lipid lateral diffusion in the DMPC/gramicidin D/water system peptide aggregation and obstruction effects. 

Ellena, J.F., L.S. Lepore, and D.S. Cafiso (1993) Estimating lipid lateral diffusion in phospholipid vesicles from 13C spin-spin relaxation. J. Rhys. Chem. 97, 2952-2957. 

Diffusion is the random movement of a particle because of an exchange of thermal energy with its environment. Membrane lipids and proteins participate in highly anisotropic translational and rotational diffusion motion. Translational diffusion in the plane of the membrane is described by the mean square lateral displacement after a time At (r ) = TD At. Lipid lateral diffusion coefficients in fluid phase bilayers are typically in the range Dj 10 to 10 cm /s (3). 

Findblom G, Oradd G, Filippov A. Lipid lateral diffusion in bilayers with phosphatidylcholine, sphingomyelin and cholesterol. An NMR study of dynamics and lateral phase separation. Chem. Phys. Lipids 2006 141 179-184. 

G. Lindblom and G. Oraedd, Lipid Lateral Diffusion and Membrane Heterogeneity , Biochim. Biophys. Acta, Biomembr., 2009, 1788, 234. 

The interaction between bacterial lipopolysaccharides (EPS) and phospholipid cell membranes was studied by various physical methods of deep rough mutant EPS (ReEPS) of Escherichia coH incorporated in phospholipid bilayers as simple models of cell membranes. SS P-NMR spectroscopic analysis suggested that a substantial part of ReEPS is incorporated into l,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayers when mixed multilamellar vesicles were prepared. Furthermore the lipid lateral diffusion coefficients measurements at various molar ratios of ReEPS/egg-PC/POPG indicated that the incorporated ReEPS reduces the diffusion coefficients of the phospholipids in the membrane. EUV formed by the ReEPS from Salmonella enterica, eventually in mixture with dilauroyl phosphatidylcholine (DEPC), have been prepared and characterized by DES, SANS and EPR. PFGSE NMR measurements have shown that water permeability through the lipid bilayer is low at room temperature. However, above a transition temperature centered at 30-35 °C, the water permeability increases. ... 

Lindblom, G., Oradd, G., Rilfors, L. and Morein, S. (2002) Regulation of lipid composition in Acholeplasma laidlawii and Escherichia coli membranes NMR studies of lipid lateral diffusion at different growth temperatures. Biochemistry 41, 11512-11515. 

Incorporation of cholesterol into model membranes increase the order parameter of the hydrocarbon chains but leaves the lipid lateral diffusion almost unaffected (12). Therefore it can be concluded that the effect of cholesterol on the packing properties of the bilayers is more important than its influence on lipid bilayer dynamics. 

Moreover, properties such as lipid lateral diffusion, lipid flip/flop, membrane elasticity and surface tension can be heavily biased in MD simulations by too small boundaries. The study in ref. 68 reported a model made of over 60 different lipid types, in a stoichiometric ratio compatible to that experimentally determined using lipidomics approaches, for a total of 20 000 lipid molecules, and simulated for 40 microseconds using coarse-grained potentials. 

A continuous lipidic cubic phase is obtained by mixing a long-chain lipid such as monoolein with a small amount of water. The result is a highly viscous state where the lipids are packed in curved continuous bilayers extending in three dimensions and which are interpenetrated by communicating aqueous channels. Crystallization of incorporated proteins starts inside the lipid phase and growth is achieved by lateral diffusion of the protein molecules to the nucleation sites. This system has recently been used to obtain three-dimensional crystals 20 x 20 x 8 pm in size of the membrane protein bacteriorhodopsin, which diffracted to 2 A resolution using a microfocus beam at the European Synchrotron Radiation Facility. 

Two principal routes of passive diffusion are recognized transcellular (la —> lb —> lc in Fig. 2.7) and paracellular (2a > 2b > 2c). Lateral exchange of phospholipid components of the inner leaflet of the epithelial bilayer seems possible, mixing simple lipids between the apical and basolateral side. However, whether the membrane lipids in the outer leaflet can diffuse across the tight junction is a point of controversy, and there may be some evidence in favor of it (for some lipids) [63]. In this book, a third passive mechanism, based on lateral diffusion of drug molecules in the outer leaflet of the bilayer (3a > 3b > 3c), wih be hypothesized as a possible mode of transport for polar or charged amphiphilic molecules. 

To diffuse rapidly in the plane of the membrane (lateral diffusion), a molecule must simply move around in the lipid environment (including the polar head groups). It need not change how it interacts with phospholipids or with water since it is constantly exposed to pretty much the same environment. Lateral diffusion can be slowed (or prevented) by interactions between membrane proteins and the cellular cytoskeleton. This spatially restricts a plasma membrane protein to a localized environment. 

Alkyl chain heterogeneities cause cell membrane bilayers to remain in the fluid state over a broad temperature range. This permits rapid lateral diffusion of membrane lipids and proteins within the plane of the bilayer. The lateral diffusion rate for an unconstrained phospholipid in a bilayer is of the order of 1 mm2 s 1 an integral membrane protein such as rhodopsin would diffuse 40nm2 s 1. 

In the fluid state, the lateral diffusion coefficient of lipids in the bilayer structure is 0( 10 1 ) m2 s-1 (the symbol O is used to indicate order of magnitude). Interestingly, it has been shown that the diffusion coefficients of phospholipids may differ greatly from the inner to the outer leaflet of the biomembrane layer [4,5]. Again, this is related to the differences in chemical... 

To integrate the equations of motion in a stable and reliable way, it is necessary that the fundamental time step is shorter than the shortest relevant timescale in the problem. The shortest events involving whole atoms are C-H vibrations, and therefore a typical value of the time step is 2fs (10-15s). This means that there are up to one million time steps necessary to reach (real-time) simulation times in the nanosecond range. The ns range is sufficient for conformational transitions of the lipid molecules. It is also sufficient to allow some lateral diffusion of molecules in the box. As an iteration time step is rather expensive, even a supercomputer will need of the order of 106 s (a week) of CPU time to reach the ns domain. 

R. Fato, M. Battino, G. P. Castelli, and G. Lenaz, Measurement of the lateral diffusion coefficients of ubiquinones in lipid vesicles by fluorescence quenching of 12-(9-anthroyl) stearate, FEES Lett. 179, 238-242 (1985). 

Substituting hx = 3.6 cm and K ip/w = K - into Eq. 28 Johnson et al. calculated solute lateral diffusion coefficients in stratum corneum bilayers from macroscopic permeability coefficients. Measurements with highly ionized or very hydrophilic compounds were not performed because of the possible transport along a nonlipoidal pathway. Comparison of the computed Aat values with experimentally determined data for fluorescent probes in extracted stratum corneum lipids [47] showed a highly similar curve shape. The diffusion coefficient for the lateral transport showed a bifunctional size dependence with a weaker size dependence for larger, lipophilic compounds (> 350 Da), than... 

Johnson ME, Berk DA, Blankschtein D, Golan DE, Jain RK, Langer RS (1996) Lateral diffusion of small compounds in human stratum corneum and model lipid bilayer systems. Biophys J 71 2656-2668. 

The prototype of a small pore-forming toxin is the S. aureus a-toxin, also called ct-hemolysin, that has been extensively investigated hy Bhakdi and coworkers. Monomers of ct-hemolysin (33 kDa) hind to the surface of erythrocytes, and after lateral diffusion within the lipid hilayer, seven monomers oligomerize to form pores in the cell membrane. The ct-hemolysin forms mushroom-shaped pores with an outer diameter of lOnm and an inner diameter of approximately 2.5 nm. Small molecules can pass through the pore and diffuse into/out of the cytosol, along with water. As a consequence of such movement, cell homeostasis is greatly disturbed and pushed into an unhealthy state. In animals, the a-hemolysin represents a major virulence factor of S. aureus which causes hemolysis as well as tissue destruction. ... 

In the free volume theory, translational diffusion of a lipid molecule in the bilayer occurs only when a free volume larger than a certain critical size appears in the vicinity of the lipid molecule. The free volume theory implies that the smaller the overall volume, the lower the probability for a molecule to associate with a free volume of a critical size. The molecules diffuse slower if the probability for a molecule to associate with a free volume of critical size is small. With increasing pressure, the overall volume decreases and the lateral diffusion is thus reduced. The activation volume for diffusion in the LC phase was calculated using the expression ... 

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