Effect of trans unsaturation on molecular organization in a phospholipid membrane.
We employed solid state (2)H NMR, complemented by computer simulations, to compare molecular organization in model membranes composed of 1-elaidoyl-2-stearoylphosphatidylcholine (t18:1-18:0PC), 1-oleoyl-2-stearoylphosphatidylcholine (c18:1-18:0PC), and 1,2-distearoylphosphatidylcholine (18:0-18:0PC). These phospholipids have elaidic acid (EA) containing a trans double bond, oleic acid (OA) containing a cis double bond, and saturated stearic acid (SA), respectively, at the sn-1 position and were synthesized with perdeuterated SA at the sn-2 position. The temperature of the chain melting transition is depressed less for t18:1-18:0PC (31.5 degrees C) than c18:1-18:0PC (7 degrees C) relative to 18:0-18:0PC (53 degrees C), reflecting the smaller deviation from the linear conformation produced by a trans as opposed to cis double bond. Acyl chain order in t18:1-18:0PC (S(CD) = 0.135) in the liquid crystalline state is much closer to that of c18:1-18:0PC (S(CD) = 0.128) than that of the substantially more ordered 18:0-18:0PC (S(CD) > 0.156), which is attributed to the reduced energy barrier to rotation about the C-C single bonds next to either a trans or cis carbon double bond. A conformation that somewhat resembles a saturated chain and an intrinsic disorder approaching that of a cis unsaturated chain characterize EA and, we speculate, may play a role in the adverse impact dietary trans fatty acids (TFA) have on biological function.
Soni
Smita P
SP
Department of Physics, Indiana University Purdue University Indianapolis, 402 North Blackford Street, Indianapolis, Indiana 46202-3273, USA.
Ward
Jesse A
JA
Sen
Stephanie E
SE
Feller
Scott E
SE
Wassall
Stephen R
SR
D000465:Algorithms; D008051:Lipid Bilayers / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D056004:Molecular Dynamics Simulation; D019301:Oleic Acid / Q000737:chemistry; D009829:Oleic Acids; D044367:Phase Transition; D010713:Phosphatidylcholines / Q000737:chemistry*; D013696:Temperature; D044242:Trans Fatty Acids / Q000737:chemistry*; D044366:Transition Temperature
D008051:Lipid Bilayers; D009829:Oleic Acids; D010713:Phosphatidylcholines; D044242:Trans Fatty Acids; D019301:Oleic Acid; C011459:elaidic acid; C067973:1-oleoyl-2-stearoylphosphatidylcholine; C010942:1,2-distearoyllecithin