Modification of lipid phase behavior with membrane-bound cryoprotectants.
Several derivatives of cholesterol containing oxyethylene headgroups with and without a terminal galactose have been synthesized in order to examine the effects of immobilizing a cryoprotectant at a membrane surface. In this work, we have studied the ability of the triethoxycholesterol (TEC) and triethoxycholesterol galactose (TEC-Gal) derivatives to modulate the phase behavior of phosphatidylcholine and phosphatidylethanolamine membranes. Methods of fluorescence polarization, 31P-NMR and freeze-fracture electron microscopy were employed to monitor these changes in lipid phase behavior. Fluorescence polarization data demonstrated the ability of the derivatives to fluidize gel state and rigidify liquid-crystalline state phosphatidylcholines in a manner similar to that observed for cholesterol. Unlike cholesterol, however, the Tm of dipalmitoylphosphatidylcholine (DPPC) was reduced in a concentration-dependent manner with each of the derivatives. Freeze-fracture electron microscopy and 31P-NMR of DOPE dispersions indicate an increase in the lamellar to hexagonal phase-transition temperature on the order of 10-20 C degrees above room temperature for mixtures with 20 mol% of the derivatives. These results are discussed in terms of the properties exhibited by compounds such as carbohydrates, which are known to serve as cryoprotectants for synthetic and biological membranes.
Goodrich
R P
RP
Department of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena 91125.
Handel
T M
TM
Baldeschwieler
J D
JD
D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol / Q000031:analogs & derivatives; D003451:Cryoprotective Agents; D005614:Freeze Fracturing; D005697:Galactosides; D008081:Liposomes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008854:Microscopy, Electron; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D013050:Spectrometry, Fluorescence / Q000379:methods; D013816:Thermodynamics
D003451:Cryoprotective Agents; D005697:Galactosides; D008081:Liposomes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C055006:triethoxycholesterol galactose; D015060:1,2-Dipalmitoylphosphatidylcholine; C040329:3-triethoxycholesterol; C020888:1,2-dielaidoylphosphatidylethanolamine; D002784:Cholesterol; C017251:1,2-oleoylphosphatidylcholine