Effects of diacylglycerols on conformation of phosphatidylcholine headgroups in phosphatidylcholine/phosphatidylserine bilayers.
The effects of five diacylglycerols (DAGs), diolein, 1-stearoyl,2-arachidonoyl-sn-glycerol, dioctanoylglycerol, 1-oleoyl,2-sn-acetylglycerol, and dipalmitin (DP), on the structure of lipid bilayers composed of mixtures of phosphatidylcholine and phosphatidylserine (4:1 mol/mol) were examined by 2H nuclear magnetic resonance (NMR). Dipalmitoylphosphatidylcholine deuterated at the alpha- and beta-positions of the choline moiety was used to probe the surface region of the membranes. Addition of each DAG except DP caused a continuous decrease in the beta-deuteron quadrupole splittings and a concomitant increase in the alpha-deuteron splittings indicating that DAGs induce a conformational change in the phosphatidylcholine headgroup. Additional evidence of conformational change was found at high DAG concentrations (> or = 20 mol%) where the alpha-deuteron peaks became doublets indicating that the two alpha-deuterons were not equivalent. The changes induced by DP were consistent with the lateral phase separation of the bilayers into gel-like and fluid-like domains with the phosphatidylcholine headgroups in the latter phase being virtually unaffected by DP. The DAG-induced changes in alpha-deuteron splittings were found to correlate with DAG-enhanced protein kinase C (PK-C) activity, suggesting that the DAG-induced conformational changes of the phosphatidylcholine headgroups are either directly or indirectly related to a mechanism of PK-C activation. 2H NMR relaxation measurements showed significant increase of the spin-lattice relaxation times for the region of the phosphatidylcholine headgroups, induced by all DAGs except DP. However, this effect of DAGs did not correlate with the DAG-induced activation of PK-C.
Department of Biology, University of California, Riverside 92521, USA.
E M
EM
Goldberg
D S
DS
Lester
D B
DB
Borchardt
R
R
Zidovetzki
D015060:1,2-Dipalmitoylphosphatidylcholine; D003903:Deuterium; D004075:Diglycerides; D008051:Lipid Bilayers; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010713:Phosphatidylcholines / Q000737:chemistry*; D010718:Phosphatidylserines / Q000737:chemistry*; D013329:Structure-Activity Relationship
D004075:Diglycerides; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D015060:1,2-Dipalmitoylphosphatidylcholine; D003903:Deuterium