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Lipid Vesicle Aggregation Induced by Cooling
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
* Author to whom correspondence should be addressed.
Received: 6 January 2010 / Accepted: 10 February 2010 / Published: 21 February 2010
Abstract: Lipid bilayer fusion is a complex process requiring several intermediate steps. Initially, the two bilayers are brought into close contact following removal of intervening water layers and overcoming electrostatic repulsions between opposing bilayer head groups. In this study we monitor by light scattering the reversible aggregation of phosphatidylcholine single shell vesicles during which adhesion occurs but stops prior to a fusion process. Light scattering measurements of dimyristoyl-sn-glycero-3-phosphocholine (DMPC), dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) in water show that lowering the temperature of about 0.14 micron single shell vesicles of DPPC (from 20 °C to 5 °C) and about 2 micron vesicles of DSPC (from 20 °C to 15 °C), but not of 1 micron vesicles of DMPC, results in extensive aggregation within 24 hours that is reversible by an increase in temperature. Aggregation of DSPC vesicles was confirmed by direct visual observation. Orientation of lipid head groups parallel to the plane of the bilayer and consequent reduction of the negative surface charge can account for the ability of DPPC and DSPC vesicles to aggregate. Retention of negatively charged phosphates on the surface and the burial of positively charged cholines within the bilayer offer an explanation for the failure of DMPC vesicles to aggregate. Lowering the temperature of 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS) vesicles from 20 °C to 5 °C failed to increase aggregation within 24 hours at Mg++/DPPS ratios that begin to initiate aggregation and fusion.
Keywords: 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC); 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC); 2-distearoyl-sn-glycero-3-phosphocholine (DSPC); 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS); aggregation; single shell vesicles; lipid head groups
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Cite This Article
MDPI and ACS Style
Howard, F.B.; Levin, I.W. Lipid Vesicle Aggregation Induced by Cooling. Int. J. Mol. Sci. 2010, 11, 754-761.
Howard FB, Levin IW. Lipid Vesicle Aggregation Induced by Cooling. International Journal of Molecular Sciences. 2010; 11(2):754-761.
Howard, Frank B.; Levin, Ira W. 2010. "Lipid Vesicle Aggregation Induced by Cooling." Int. J. Mol. Sci. 11, no. 2: 754-761.