2H NMR Studies of Isomeric .omega.3 and .omega.6 Polyunsaturated Phospholipid Membranes

The properties of phosphatidylcholines (PCs) having a perdeuterated stearic acid, 18:0d35, in the sn-1 position and the fatty acid 18:0, 18:1 omega 9, 18:2 omega 6, 18:3 omega 3, 20:4 omega 6, 20:5 omega 3, or 22:6 omega 3 at the sn-2 position were investigated in a matrix of dioleoylphosphatidylethanolamine (DOPE) by 2H and 31P NMR spectroscopy. At a mole ratio of DOPE/PC = 5:1, the lipids form liquid crystalline lamellar phases below 40 degrees C and coexisting lamellar, inverse hexagonal (Hll), and cubic phases at higher temperatures. The sn-1 chain of the PCs in a DOPE matrix is appreciably more ordered than in pure PCs, corresponding to an increase in the hydrophobic bilayer thickness of approximately 1 A. Distearoylphosphatidylcholine in the DOPE matrix has a higher sn-1 chain order than the unsaturated PCs. We observed distinct differences in the lipid order of upper and lower sections of the hydrocarbon chains caused by changes of temperature, unsaturation, headgroups, and ethanol. Unsaturation lowers chain order, mostly in the lower third of the hydrocarbon chains. By contrast, the increase in chain order caused by the DOPE matrix and the decrease in order with increasing temperature have a constant magnitude for the upper two-thirds of the chain and are smaller for the lower third. Addition of 2 M ethanol reduced order parameters, in effect reversing the increase in chain order caused by the DOPE matrix.

Section: Discussionmentioning

confidence: 99%

Effect of unsaturation on the chain order of phosphatidylcholines in a dioleoylphosphatidylethanolamine matrix

Separovic¹,

Gawrisch²

1996

“…Membrane properties are a consequence of lipid-lipid interactions, which are manifested over a broad range of length scales (7,8). At molecular scales (1-10 nm), lipid interactions determine molecular packing within membranes, characterized by structural parameters accessible by small-angle x-ray scattering (SAXS) (9,10) and by lipid order parameters obtained from solid-state NMR spectroscopy (10,11). The exact molecular packing within lipid bilayers is determined by the balance of forces between hydrophilic headgroups and hydrophobic chains, with the lipid headgroup having a dominant role in the case of saturated and monounsaturated acyl chains (10,12,13).…”

Section: Introductionmentioning

confidence: 99%

“…This powerful experimental technique provides an order parameter profile that describes the ordering of lipid acyl chains within the bilayer. A large order parameter means the motion of the acyl chains is strongly constrained, corresponding to tighter molecular packing, whereas small order parameters indicate more disorder and looser packing (8,(10)(11)(12). For this part of the study, we used deuterium-labeled lipids in PS/PC mixtures identified by x-ray scattering to be in the MLV-ULV transition range.…”

Section: Introductionmentioning

confidence: 99%

Effects of Lipid Interactions on Model Vesicle Engulfment by Alveolar Macrophages

Justice

Petrusca

Rogozea

et al. 2014

The engulfment function of macrophages relies on complex molecular interactions involving both lipids and proteins. In particular, the clearance of apoptotic bodies (efferocytosis) is enabled by externalization on the cell target of phosphatidylserine lipids, which activate receptors on macrophages, suggesting that (local) specific lipid-protein interactions are required at least for the initiation of efferocytosis. However, in addition to apoptotic cells, macrophages can engulf foreign bodies that vary substantially in size from a few nanometers to microns, suggesting that nonspecific interactions over a wide range of length scales could be relevant. Here, we use model lipid membranes (made of phosphatidylcholine, phosphatidylserine, and ceramide) and rat alveolar macrophages to show how lipid bilayer properties probed by small-angle x-ray scattering and solid-state (2)H NMR correlate with engulfment rates measured by flow cytometry. We find that engulfment of protein-free model lipid vesicles is promoted by the presence of phosphatidylserine lipids but inhibited by ceramide, in accord with a previous study of apoptotic cells. We conclude that the roles of phosphatidylserine and ceramide in phagocytosis is based, at least in part, on lipid-mediated modification of membrane physical properties, including interactions at large length scales as well as local lipid ordering and possible domain formation.

“…The precise structure of the membrane is labile and constantly changing. Nuclear magnetic resonance (NMR) studies have given us data on the mean orientations of hydrocarbon tails (Borle and Seelig, 1983;Rice and Oldfield, 1979;McCabe et al, 1994). NMR and neutron and x-ray diffraction have given us data on the mean orientations of the headgroups (Wiener and White, 1992b;Sanders, 1993).…”

Section: Introductionmentioning

confidence: 99%

Incorporation of surface tension into molecular dynamics simulation of an interface: a fluid phase lipid bilayer membrane

Chiu

Clark

Balaji

et al. 1995

372

405

In this paper we report on the molecular dynamics simulation of a fluid phase hydrated dimyristoylphosphatidylcholine bilayer. The initial configuration of the lipid was the x-ray crystal structure. A distinctive feature of this simulation is that, upon heating the system, the fluid phase emerged from parameters, initial conditions, and boundary conditions determined independently of the collective properties of the fluid phase. The initial conditions did not include chain disorder characteristic of the fluid phase. The partial charges on the lipids were determined by ab initio self-consistent field calculations and required no adjustment to produce a fluid phase. The boundary conditions were constant pressure and temperature. Thus the membrane was not explicitly required to assume an area/phospholipid molecule thought to be characteristic of the fluid phase, as is the case in constant volume simulations. Normal to the membrane plane, the pressure was 1 atmosphere, corresponding to the normal laboratory situation. Parallel to the membrane plane a negative pressure of -100 atmospheres was applied, derived from the measured surface tension of a monolayer at an air-water interface. The measured features of the computed membrane are generally in close agreement with experiment. Our results confirm the concept that, for appropriately matched temperature and surface pressure, a monolayer is a close approximation to one-half of a bilayer. Our results suggest that the surface area per phospholipid molecule for fluid phosphatidylcholine bilayer membranes is smaller than has generally been assumed in computational studies at constant volume. Our results confirm that the basis of the measured dipole potential is primarily water orientations and also suggest the presence of potential barriers for the movement of positive charges across the water-headgroup interfacial region of the phospholipid.