Dehydration induces lateral expansion of polyunsaturated 18:0-22:6 phosphatidylcholine in a new lamellar phase.
To gain a better understanding of the biological role of polyunsaturated phospholipids, infrared (IR) linear dichroism, NMR, and x-ray diffraction studies have been conducted on the lyotropic phase behavior and bilayer dimensions of sn-1 chain perdeuterated 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (SDPC-d35), a mixed-chain saturated (18:0)-polyunsaturated (22:6 omega 3) lipid. SDPC films were hydrated at definite values of temperature (T) and relative humidity (RH). In excess water, the lipid forms exclusively lamellar phases in the temperature range 0--50 degrees C. Upon dehydration the lipid undergoes the main phase transition between the liquid-crystalline (L(alpha)) and gel (L(beta)) phase at T < 15 degrees C. Both the saturated and polyunsaturated chains adopt a stretched conformation in the L(beta) phase, presumably the all-trans (stearoyl) and angle iron or helical (docosahexaenoyl) one. A new fluid lamellar phase (L(alpha)') was found in partially hydrated samples at T > 15 degrees C. SDPC membranes expand laterally and contract vertically in the L(alpha)' phase when water was removed. This tendency is in sharp contrast to typical dehydration-induced changes of membrane dimensions. The slope of the phase transition lines in the RH-T phase diagram reveal that the lyotropic L(alpha)'-L(alpha) and L(beta)-L(alpha) transitions are driven by enthalpy and entropy, respectively The possible molecular origin of the phase transitions is discussed. The properties of SDPC are compared with that of membranes of monounsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d31).
Binder
H
H
University of Leipzig, Institute of Medical Physics and Biophysics, D-04103 Leipzig, Germany. binder@rz.uni-leipzig.de
Gawrisch
K
K
D002942:Circular Dichroism; D003890:Desiccation; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000378:metabolism*; D013055:Spectrophotometry, Infrared; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics; D014867:Water / Q000378:metabolism; D014961:X-Ray Diffraction
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; C029449:polyene phosphatidylcholine; D014867:Water