1-2-oleoylphosphatidylcholine and phosphorylethanolamine

The nanomechanical response of supported lipid bilayers has been studied by force spectroscopy with atomic force microscopy. We have experimentally proved that the amount of ions present in the measuring system has a strong effect on the force needed to puncture a 1,2-dimyristoyl-sn-glycero-3-phosphocholine bilayer with an atomic force microscope tip, thus highlighting the role that monovalent cations (so far underestimated, e.g., Na(+)) play upon membrane stability. The increase in the yield threshold force has been related to the increase in lateral interactions (higher phospholipid-phospholipid interaction, decrease in area per lipid) promoted by ions bound into the membrane. The same tendency has also been observed for other phosphatidylcholine bilayers, namely, 2-dilauroyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, and 1,2-dioleoyl-sn-3-phosphocholine, and also for phosphatidylethanolamine bilayers such as 1-palmitoyl-2-oleoyl-sn-3-phosphoethanolamine. Finally, this effect has been also tested on a natural lipid bilayer (Escherichia coli lipid extract), showing the same overall tendency. The kinetics of the process has also been studied, together with the role of water upon membrane stability and its effect on membrane nanomechanics. Finally, the effect of the chemical structure of the phospholipid molecule on the nanomechanical response of the membrane has also been discussed.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Biophysical Phenomena; Biophysics; Dimyristoylphosphatidylcholine; Dose-Response Relationship, Drug; Escherichia coli; Ethanolamines; Ions; Kinetics; Lipid Bilayers; Lipids; Microscopy, Atomic Force; Nanotechnology; Phosphatidylcholines; Phosphatidylethanolamines; Phospholipids; Phosphorylcholine; Silicon Compounds; Sodium; Sodium Chloride; Spectrophotometry

The effects of nonlamellar-prone lipids, diacylglycerol and phosphatidylethanolamine (PE), on the kinetic association of SecA with model membranes were examined by measuring changes in the intrinsic emission fluorescence with a stopped-flow apparatus. Upon interaction with standard liposomes composed of 50 mol% dioleolyphosphatidylcholine (DOPC) and 50 mol% of dioleoylphosphatidylglycerol (DOPG), the intrinsic fluorescence intensity of SecA was decreased after a lapse of time with a rate constant of 0.0049 s(-1). When the DOPC of the standard vesicles was gradually replaced with either dioeloyl PE (DOPE) or Escherichia coli (E. coli) PE, the rate constant increased appreciably as a function of PE concentration, in the order DOPE > E. coli PE. In addition, when the PE of E. coli PE/DOPG (50/50) vesicles was replaced with more than 5 mol% dioleoylglycerol (DOG), the rate constant further increased by 40%. The incorporation of nonlamellar-prone lipids in the vesicles also enhanced the binding of SecA to model membranes in the order DOPE > or = E. coli PE/DOG > E. coli PE > DOPC. These results provide the first kinetic evidence for the importance of nonlamellar-prone phospholipids for the association rate of SecA with membranes.

Topics: Adenosine Triphosphatases; Bacterial Proteins; Diglycerides; Escherichia coli Proteins; Ethanolamines; Flow Injection Analysis; Glycerophospholipids; Kinetics; Lipid Bilayers; Lipids; Liposomes; Membrane Transport Proteins; Membranes, Artificial; Models, Biological; Phosphatidylcholines; Phosphatidylethanolamines; Phosphatidylglycerols; Protein Binding; SEC Translocation Channels; SecA Proteins; Spectrometry, Fluorescence