Lipids traffic

Van Meer, G. 1989. Lipid traffic in animal cells. Ann. Rev. Cell Biol. 5, 247-275. 

Pagano RE, Watanabe R, Wheatley C, Dominguez M. Applications of BODIPY-sphingolipid analogs to study lipid traffic and 164. metabolism in cells. Methods Enzymol. 2000 312 523-534. 

Fig. 4 The lipid influx/efflux rheostat model maintains lipid uptake and export mechanisms in a balance. ATP synthase is regulated by apoA-I or apoE leading to enhanced conversion of ATP to ADP. The absence of apoA-I would lead to enhanced sinking in phagocytosis since actin can bind ATP, polymerize, and form F-actin which is essential for type 11 phagocytosis. Hence apoA-I could lead to increased influx. On the other hand, apoA-I binds to ABCAl leading to enhanced lipid efflux. Dysfunction of this equilibrium may lead to severe disturbances of cellular lipid traffic. This is obvious in Tangier disease patients where ABCAl is inoperative and apoA-/-dependent cholesterol is absent. Cholesterol influx, however, is enhanced due to apoA-Z-dependent stimulation of ATP synthase B leading to cholesteryl ester formation and enhanced foam cell formation...

The most abundant membranes in nature are the thylakoids inside chloroplasts of green plants. A surprising amount of lipid traffic is involved in the assembly of these membranes. Almost all the acyl chains that form the core of the photosynthetic membranes are first produced by fatty acid synthase in the chloroplast. In most plants these acyl chains are then exported to the ER where they become esterified to glycerol, desaturated while they are part of phosphatidylcholine and then are returned to the plastid. The exact mechanisms for the export and return of acyl chains are still uncertain although much has been learned (Chapter 17) [10]. The export from plastids across the chloroplast envelope membranes is known to involve a fatty acid intermediate, and probably is a channeled or facilitated process rather than free diffusion because only a tiny pool of free fatty acid is ever detected (A. Koo, 2004). An acyl-CoA synthetase on the envelope membrane is believed to quickly convert the exported fatty acid to a thioester form that is then a substrate for acyltransferases. Transfer of acyl groups to the ER may occur via diffusion of the acyl-CoAs however, recent evidence suggests this initial acyl transfer reaction involves acylation of lyso-phosphatidylcholine and may occur at the chloroplast envelope. 

The mechanism of this transport is presently unknown, but the results are consistent with a soluble carrier mechanism such as PC transfer protein, or transport at zones of apposition between membranes that facilitate rapid intermembrane transfer. Work by Pichler and colleagues has identified a subfraction of the ER that associates closely with the plasma membrane in yeast (H. Pichler, 2001). Future studies examining the effects of agents or mutations that disrupt these intracellular membrane associations will be critical for determining their role in lipid traffic. 

Graham, T.R. 2004. Rippases and vesicle-mediated protein transport. Trends Cell Biol. 14 670-677. Holthuis, J.C., Levine, T.P. 2005. Lipid traffic floppy drives and a superhighway. Nat. Rev. Mol. Cell Biol. 6 209-220. 

Grellier, P., Rigomier, D., Clavey, V., Fruchart, J.-C. and Schrevel, J. (1991) Lipid traffic between high density lipoproteins and Plasmodium falciparum-infected red blood cells. J. Cell Biol. 112 261-111. 

Holthuis JC and Levine TP. Lipid Traffic Floppy Drives and a Superhighway. Nature Rev. Mol. Cell Biol. 6 209-2020 (2005). 

Biological Applications Measuring activity of a hydrolase studying lipid traffic, membrane traffic inositol phosphorylceramide synthase activity assay ... 

Togo, T. Disruption of the plasma membrane stimulates rearrangement of microtubules and lipid traffic toward the wound site. J. Cell Sci. 2006,119, 2780-2786. 

Parton RG, Richards AA. Lipid rafts and caveolae as portals for endocytosis new insights and common mechanisms. Traffic 2003 4(11) 724. 

Fullekrug J, Simons K. Lipid rafts and apical membrane traffic. Ann N YAcad Sci. 2004 1014 164-169. 

Roth, M.G. (1999) Lipid regulators of membrane traffic through the Golgi complex. Trends Cell Biol. 9, 174-179. 

The biological function of lipid asymmetry and of proteins involved in the transmembrane traffic of lipids is multiple. Rapid reorientation of phospholipids in ery-... 

Palade GE (1953) Fine structure of blood capillaries. J Appl Physiol 24 1424 Parton RG, Richards AA (2003) Lipid rafts and caveolae as portals for endocytosis new insights and common mechanisms. Traffic 4 724-738 Powell DW (1981) Barrier function of epithelia. Am J Physiol Gastrointest Liver Physiol 241 G275-G288... 

Cockcroft, S., and De Matteis, M.A., 2001, Inositol lipids as spatial regulators of membrane traffic. J. Membr. Biol. 180 187-194. 

Takenawa, T. and Itoh, T., 2001, Phosphoinositides, key molecules for regulation of actin cytoskeletal organization and membrane traffic from the plasma membrane. Biochim. Biophys. Acta-Mol. Cell Biol. Lipids 1533 190-206. 

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