High-resolution 13C NMR study of pressure effects on the main phase transition in L-alpha-dipalmitoyl phosphatidylcholine vesicles

Tailoring the nuclear Overhauser effect for the study of small and medium-sized molecules by solvent viscosity manipulation

The nuclear Overhauser effect (NOE) is a consequence of cross-relaxation between nuclear spins mediated by dipolar coupling. Its sensitivity to internuclear distances has made it an increasingly important tool for the determination of through-space atom proximity relationships within molecules of sizes ranging from the smallest systems to large biopolymers. With the support of sophisticated FT-NMR techniques, the NOE plays an essential role in structure elucidation, conformational and dynamic investigations in liquid-state NMR. The efficiency of magnetization transfer by the NOE depends on the molecular rotational correlation time, whose value depends on solution viscosity. The magnitude of the NOE between ¹H nuclei varies from +50% when molecular tumbling is fast to -100% when it is slow, the latter case corresponding to the spin diffusion limit. In an intermediate tumbling regime, the NOE may be vanishingly small. Increasing the viscosity of the solution increases the motional correlation time, and as a result, otherwise unobservable NOEs may be revealed and brought close to the spin diffusion limit. The goal of this review is to report the resolution of structural problems that benefited from the manipulation of the negative NOE by means of viscous solvents, including examples of molecular structure determination, conformation elucidation and mixture analysis (the ViscY method).

Dependence on acyl chain length of energy and volume parameters of the gel to liquid-crystalline transition of 1,2-diacylphosphatidylcholines. Theoretical consideration

The effect of acyl chain length on energy and volume parameters of gel to liquid-crystal transitions in phospholipids is analyzed. It is demonstrated that simple structural and thermodynamic considerations allow predicting some thermodynamic and volume characteristics of transitions and their dependencies on the acyl chains length.

A direct protein kinase B-targeted anti-inflammatory activity of cordycepin from artificially cultured fruit body of Cordyceps militaris

Background:

Cordyceps militaris is one of well-known medicinal mushrooms with anti-inflammatory, anti-cancer, anti-diabetic, and anti-obesity activities.

Objective:

The objective of the following study is to isolate chemical components from the ethanol extract (Cm-EE) from Cordyceps militaris and to evaluate their anti-inflammatory activities.

Materials and Methods:

Column chromatographic separation was performed and anti-inflammatory roles of these compounds were also examined by using NO production and protein kinase B (AKT) activity assays.

Results:

From Cm-EE, 13 constituents, including trehalose (1), cordycepin (2), 6-hydroxyethyladenosine (3), nicotinic amide (4), butyric acid (5), β-dimorphecolic acid (6), α-dimorphecolic acid (7), palmitic acid (8), linoleic acid (9), cordycepeptide A (10), 4-(2-hydroxy-3-((9E,12E)-octadeca-9,12-dienoyloxy)propoxy)-2-(trimethylammonio)butanoate (11), 4-(2-hydroxy-3-(palmitoyloxy)propoxy)-2-(trimethylammonio)butanoate (12), and linoleic acid methyl ester (13) were isolated. Of these components, compound 2 displayed a significant inhibitory effect on NO production in lipopolysaccharide (LPS)-activated RAW264.7 cells. Furthermore, this compound strongly and directly suppressed the kinase activity of AKT, an essential signalling enzyme in LPS-induced NO production, by interacting with its ATP binding site.

Conclusion:

C. militaris could have anti-inflammatory activity mediated by cordycepin-induced suppression of AKT.

High hydrostatic pressure effects investigated by neutron scattering on lipid multilamellar vesicles

The effects of high hydrostatic pressure on the structure and dynamics of model membrane systems were investigated using neutron scattering. Diffraction experiments show shifts of the pre- and main-phase transitions of multilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) to higher temperatures with increased pressure which are close to results observed previously by other techniques, namely (10.4 ± 1.0) K kbar(-1) and (20.0 ± 0.5) K kbar(-1) for the two transitions. Backscattering spectroscopy reveals that the mean square displacements in the liquid phase are about 10% smaller at 300 bar and about 20% smaller at 600 bar compared to atmospheric pressure, whereas in the gel phase below the main phase transition the mean square displacements show a smaller difference in the dynamics of the three pressure values within the studied pressure range.

Pressure-induced phase transitions of lipid bilayers observed by fluorescent probes Prodan and Laurdan

The fluorescence spectra of 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and 6-dodecanoyl-2-(dimethylamino)naphthalene (Laurdan) in bilayer membranes of 1,2-distearoylphosphatidylcholine (DSPC) were observed as a function of pressure at constant temperature. The emission spectra of Prodan and Laurdan varied with the pressure-induced states of bilayer membranes. The maximum emission wavelength (lambda(max)) of Prodan characteristic of the liquid crystalline (L(alpha)), lamellar gel (L(beta)') and pressure-induced interdigitated gel (L(beta)I) phases of the DSPC bilayer was 480, 440 and 500 nm, respectively. On the other hand, the lambda(max) of Laurdan characteristic of the L(alpha) and L(beta)' phases was 480 and 440 nm in a similar manner as Prodan probe. However, no change in the lambda(max) was observed in spite of the occurrence of the interdigitation of bilayer. Since the lambda(max) reflects the solvent property around the probe molecules, we could speculate about the location of fluorescent probe in the bilayer membranes. In the L(alpha) phase the same chromophore group of Prodan and Laurdan probes distributes around phosphate group of lipid (i.e., polar region). The transformation of bilayer into the L(beta)' phase causes the Prodan and Laurdan molecules to move into the glycerol backbone (i.e., less polar) region. In the ripple gel (P(beta)') phase, the emission spectrum of Prodan shows a broad peak at about 480 nm and a shoulder around 440 nm, which means that the Prodan molecules are widespread over the wide range from the glycerol backbone to the hydrophilic part of bilayer. The P(beta)'/L(beta)I phase transition causes the Prodan molecule to squeeze out from the glycerol backbone region and to move the hydrophilic region near the bilayer surface. Contrarily, the Laurdan molecule was not squeezed out from the glycerol backbone region because the long acyl chain of Laurdan serves as an anchor in the hydrophobic core of bilayer. The ratio of fluorescence intensity of Prodan at 480 nm to that at 440 nm, F(480)/F(440), is available to observation of bilayer phase transitions. The plot of F(480)/F(440) versus pressure seems to be useful for the recognition of bilayer phase transition, especially the bilayer interdigitation.

Effect of deuterium oxide on the thermodynamic quantities associated with phase transitions of phosphatidylcholine bilayer membranes

The bilayer phase transitions of three kinds of phospholipids, dipalmitoylphosphatidylcholine (DPPC), distearoylphosphatidylcholine (DSPC) and dihexadecylphosphatidylcholine (DHPC), in deuterium oxide (D(2)O) and hydrogen oxide (H(2)O) were observed by differential scanning calorimetry (DSC) under ambient pressure and light-transmittance measurements under high pressure. The DSC measurements showed that the substitution of H(2)O by D(2)O affected the pretransition temperatures and the main-transition enthalpies of all PC bilayers. The temperature-pressure phase diagrams for these PC bilayer membranes in both solvents were constructed by use of the data of light-transmittance measurements. Regarding the main transition of all PC bilayer membranes, there was no appreciable difference between the transition temperatures in D(2)O and H(2)O under high pressure. On the other hand, the phase transitions among the gel phases including the pretransition were significantly affected by the solvent substitution. The thermodynamic quantities of phase transitions for the PC bilayer membranes were evaluated and the differences in thermodynamic properties by the water substitution were considered from the difference of interfacial-free energy per molecule in the bilayer in both solvents. It was proved that the substitution of H(2)O by D(2)O causes shrinkage of the molecular area of phospholipid at bilayer interface due to the difference in bond strength between deuterium and hydrogen bonds and produces the great influence on the bilayer phase with the smaller area. Further, the induction of bilayer interdigitation in D(2)O turned out to need higher pressures than in H(2)O.

Effect of pressure on the Prodan fluorescence in bilayer membranes of phospholipids with varying acyl chain lengths

The fluorescence spectra of 6-propionyl-2-(dimethylamino)naphthalene (Prodan) were observed as a function of pressure for the bilayer membrane systems of dilauroylphosphatidylcholine (DLPC), dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and distearoylphosphatidylcholine (DSPC). The wavelength of the emission maximum, lambdamax, was found to be 480, 430, and 500 nm for the liquid crystalline (Lalpha), ripple gel (P'beta), and pressure-induced interdigitated gel (LbetaI) phase, respectively. Since the lambdamax reflects the solvent property around the probe molecules, we could speculate on the location of the Prodan molecules in the bilayer membranes; in the Lalpha phase of the lipid bilayer, the Prodan molecules distribute around the phosphate of the lipids (i.e. the polar region). The Lalpha/P'beta phase transition caused the Prodan molecules to move into the less polar region near the glycerol backbone. The fluorescence intensity of the Prodan in the P'beta phase was dependent on the chain length of the lipids and on pressure; the shorter the chain length of the lipid, the stronger the fluorescence intensity of the Prodan. Moreover, for the DLPC bilayer membrane system, the fluorescence intensity at 430 nm increased with increasing pressure, indicating that the partition of Prodan into the DLPC bilayer membrane is promoted by applying pressure. In the case of the DPPC and DSPC bilayers, as the pressure increased further, the pressure-induced interdigitation caused the Prodan molecules to squeeze out of the glycerol backbone region and to move the hydrophilic region near the bilayer surface. The ratio of fluorescence intensity at 480 nm to that at 430 nm, F480/F430, showed a sharp change at the phase-transition pressure. In the case of the DPPC and DSPC bilayers, the values of F480/F430 showed an abrupt increase above a certain pressure higher than the Lalpha/P'beta transition pressure, which corresponds to the interdigitation from the P'beta to the LbetaI phase. The plot of F480/F430 versus pressure is available for recognition of the bilayer phase transitions, especially the bilayer interdigitation.

Thermotropic and barotropic phase transitions of N-methylated dipalmitoylphosphatidylethanolamine bilayers

In order to understand the effect of polar head group modification on the thermotropic and barotropic phase behavior of phospholipid bilayer membranes, the phase transitions of dipalmitoylphosphatidylethanolamine (DPPE), dipalmitoylphosphatidyl-N-methylethanolamine (DPMePE), dipalmitoylphosphatidyl-N,N-dimethylethanolamine (DPMe2PE) and dipalmitoylphosphatidylcholine (DPPC) bilayer membranes were observed by differential scanning calorimetry and high-pressure optical methods. The temperatures of the so-called main transition from the gel (L(beta)) or ripple gel (P(beta)') phase to the liquid crystalline (L(alpha)) phase were almost linearly elevated by applying pressure. The slope of the temperature-pressure boundary, dT/dp, was in the range of 0.220-0.264 K MPa(-1) depending on the number of methyl groups in the head group of lipids. The main-transition temperatures of N-methylated DPPEs decreased with increasing size of head group by stepwise N-methylation. On the other hand, there was no significant difference in thermodynamic quantities of the main transition between the phospholipids. With respect to the transition from the subgel (L(c)) phase to the lamellar gel (L(beta) or L(beta)') phase, the transition temperatures were also elevated by applying pressure. In the case of DPPE bilayer the L(c)/L(beta) transition appeared at a pressure higher than 21.8 MPa. At a pressure below 21.8 MPa the L(c)/L(alpha) transition was observed at a temperature higher than the main-transition temperature. The main (L(beta)/L(alpha)) transition can be recognized as the transformation between metastable phases in the range from ambient pressure to 21.8 MPa. Polymorphism in the gel phase is characteristic of DPPC bilayer membrane unlike other lipid bilayers used in this study: the L(beta)', P(beta)' and pressure-induced interdigitated gel (L(beta)I) phases were observed only in the DPPC bilayer. Regarding the bilayers of DPPE, DPMePE and DPMe2PE, the interdigitation of acyl chain did not appear even at pressures as high as 200 MPa.

Synchrotron X-ray and neutron small-angle scattering of lyotropic lipid mesophases, model biomembranes and proteins in solution at high pressure

In this review we discuss the use of X-ray and neutron diffraction methods for investigating the temperature- and pressure-dependent structure and phase behaviour of lipid and model biomembrane systems. Hydrostatic pressure has been used as a physical parameter for studying the stability and energetics of lipid mesophases, but also because high pressure is an important feature of certain natural membrane environments and because the high pressure phase behaviour of biomolecules is of importance for several biotechnological processes. Using the pressure jump relaxation technique in combination with time-resolved synchrotron X-ray diffraction, the kinetics of different lipid phase transformations was investigated. The techniques can also be applied to the study of other soft matter and biomolecular phase transformations, such as surfactant phase transitions and protein un/refolding reactions. Several examples are given. In particular, we present data on the pressure-induced unfolding and refolding of small proteins, such as Snase. The data are compared with the corresponding results obtained using other trigger mechanisms and are discussed in the light of recent theoretical approaches.

Investigation of the effect of high hydrostatic pressure on proteins and lipidic membranes by dynamic fluorescence spectroscopy

Dynamic fluorescence spectroscopy brings new insight into the functional and structural changes of biological molecules under moderate and high hydrostatic pressure. The principles of time-resolved fluorescence methods are briefly described and the resulting type of information is summarized. A first set of selected applications of the use of dynamic fluorescence on pressure effects on proteins in terms of denaturation, ternary and quaternary structure, aggregation and also interaction with DNA are presented. A second set of applications is devoted to the effect of pressure and of cholesterol on lateral heterogeneity of lipidic membranes.

Using O2 to probe membrane immersion depth by 19F NMR

A fluorinated detergent, CF(3)(CF(2))(5)C(2)H(4)-O-maltose, was reconstituted into a lipid bilayer model membrane system to demonstrate the feasibility of determining solvent accessibility and membrane immersion depth of each fluorinated group by (19)F NMR. Apolar oxygen, which is known to partition with an increasing concentration gradient toward the hydrophobic membrane interior, exhibits a range of paramagnetic relaxation effects on (19)F nuclei, depending on its depth in the membrane. This effect, which is predominately associated with spin-lattice relaxation rates (R(1)) and chemical shifts, can be amplified greatly with minimal line broadening by increasing the partial pressure of O(2) at least 100-fold (i.e., P(O(2)) greater than 20 bar). The differences of longitudinal relaxation rates at 20 bar of oxygen pressure to those under ambient pressure (R(1)(20bar) - R(1)(0)) are largest for those fluorine groups expected to be most deeply buried in the membrane bilayer. This result contrasts with the reverse trend, which is observed on addition of a membrane surface-associated paramagnetic species, 4-(N,N-dimethyl-N-hexadecyl) ammonium-2,2,6,6-tetramethylpiperidine-1-oxyl iodide (CAT-16) at ambient pressures. Thus, differential relaxation rates may be observed in (19)F-labeled membrane-associated molecules resulting from the addition of apolar oxygen under high pressure. The results demonstrate that the degree of solvent accessibility and membrane immersion depth of specific fluorinated species in membrane-associated macromolecules can be probed by (19)F NMR.

Barotropic phase transitions of dioleoylphosphatidylcholine and stearoyl-oleoylphosphatidylcholine bilayer membranes

In order to understand the effect of cis unsaturation on the thermotropic and barotropic phase behavior of phospholipid bilayer membranes, the phase transitions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) bilayer membranes were observed by high-pressure optical method. With respect to DOPC bilayer membrane, the so-called main transition between the liquid crystalline (Lalpha) and the lamellar gel (Lbeta) phases was observed in water at above 0 degrees C under high pressure, in addition to the transition between the Lalpha and the lamellar crystalline (L(C)) phases in 50% aqueous ethylene glycol. The pressure of main transition increased linearly with an increase in temperature. Extrapolation of temperature (T)-pressure (P) phase boundary to ambient pressure suggests the temperature of the main transition to be -40.3 degrees C, which has never been found by the DSC method. On the other hand, the temperature of L(C)/Lalpha phase transition in 50% aqueous ethylene glycol was found to be -12.0 degrees C at ambient pressure. The main transition temperatures for DSPC, SOPC and DOPC are 55.6, 6.7 and -40.3 degrees C, respectively, at ambient pressure. The substitution of cis unsaturated chain for saturated chains of DSPC brings about the depression of the main transition temperature by about 48 (+/-1) degrees C for each chain. The volume changes (deltaV) associated with the transitions were calculated from the transition enthalpy (deltaH) and the slope of T-P diagram (dT/dP) by means of the Clapeyron-Clausius equation. The value of deltaV for the main transition of SOPC bilayer membranes was reduced to half the volume change for DSPC bilayers, which means the introduction of the cis double bond in the acyl chain of lipids brings about the reduction of deltaV because of the disordered packing of unsaturated chains in the gel phase of lipid bilayer membranes.

Effect of hydrostatic pressure on water penetration and rotational dynamics in phospholipid-cholesterol bilayers

The effect of high hydrostatic pressure on the lipid bilayer hydration, the mean order parameter, and rotational dynamics of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) cholesterol vesicles has been studied by time-resolved fluorescence spectroscopy up to 1500 bar. Whereas the degree of hydration in the lipid headgroup and interfacial region was assessed from fluorescence lifetime data using the probe 1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH), the corresponding information in the upper acyl chain region was estimated from its effect on the fluorescence lifetime of and 3-(diphenylhexatrienyl)propyl-trimethylammonium (TMAP-DPH). The lifetime data indicate a greater level of interfacial hydration for DPPC bilayers than for POPC bilayers, but there is no marked difference in interchain hydration of the two bilayer systems. The addition of cholesterol at levels from 30 to 50 mol% to DPPC has a greater effect on the increase of hydrophobicity in the interfacial region of the bilayer than the application of hydrostatic pressure of several hundred to 1000 bar. Although the same trend is observed in the corresponding system, POPC/30 mol% cholesterol, the observed effects are markedly less pronounced. Whereas the rotational correlation times of the fluorophores decrease in passing the pressure-induced liquid-crystalline to gel phase transition of DPPC, the wobbling diffusion coefficient remains essentially unchanged. The wobbling diffusion constant of the two fluorophores changes markedly upon incorporation of 30 mol% cholesterol, and increases at higher pressures, also in the case of POPC/30 mol% cholesterol. The observed effects are discussed in terms of changes in the rotational characteristics of the fluorophores and the phase-state of the lipid mixture. The results demonstrate the ability of cholesterol to adjust the structural and dynamic properties of membranes composed of different phospholipid components, and to efficiently regulate the motional freedom and hydrophobicity of membranes, so that they can withstand even drastic changes in environmental conditions, such as high external hydrostatic pressure.

Effects of hydrostatic pressure on bilayer phase behavior and dynamics of dilauroylphosphatidylcholine

Deuterium nuclear magnetic resonance spectroscopy was used to study the thermotropic phase behavior of dilauroylphosphatidylcholine (DLPC) bilayers at pressures up to 221 MPa. Pressure was found to separate the liquid crystal to gel transition from the gel to ordered crystalline phase transition. The jump in chain order observed on cooling through the transition into the gel phase was found to be small and thus consistent with the trend in longer chain saturated diacyl phosphatidylcholines. On cooling, DLPC was observed to enter an unusual state above the transition into the gel phase. This unusual state displayed fluid-like conformational order but short transverse relaxation times. It was found to be much better pronounced and to span a broader temperature range at elevated pressure than at lower pressures. Transverse relaxation measurements of deuterons on the chain alpha-carbons revealed a substantial slowing of molecular motions within the temperature range of the unusual fluid phase. The observation of such a phase at high pressure appears to be consistent with recent reports of an unusual fluid phase, Lx, in DLPC at ambient pressure.

Hydrostatic pressure-induced conformational changes in phosphatidylcholine headgroups: a 2H NMR study

The effects of pressure and temperature on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phosphocholine headgroup conformations were examined using deuterium nuclear magnetic resonance. Isothermal compression was found to produce a decrease in the choline alpha deuteron quadrupole splitting and increases in the choline beta and gamma deuteron quadrupole splittings. A similar counterdirectional change, seen in the presence of positive surface charge, has been attributed to tilting of the headgroup away from the bilayer surface in response to the torque exerted on the phosphocholine dipole by positive surface charges. The direction of the change in headgroup deuteron quadrupole splitting is consistent with the pressure-induced reduction in area per lipid in the liquid crystalline phase, which can be inferred from the ordering of phospholipid acyl chains under comparable conditions. The temperature dependences of the headgroup deuteron quadrupole splittings were also examined. It was found that at elevated pressure, the alpha splitting was insensitive to temperature, whereas the beta and gamma splittings decreased. The response of the beta deuteron splitting to temperature was found to be weaker at elevated pressure than at ambient pressure.

High pressure 2H-NMR study of the order and dynamics of selectively deuterated dipalmitoyl phosphatidylcholine in multilamellar aqueous dispersions

High pressure 2H multipulse NMR techniques were used to investigate the effects of pressure on the structure and dynamics of selectively deuterated 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) multilamellar aqueous dispersions. The samples were deuterated on both chains at positions 2, 9, or 13. The deuterium lineshapes, the spin-lattice relaxation times, T1, and the spin-spin relaxation times, T2, were measured as a function of pressure from 1 bar to 5 kbar at 50 degrees C for the three deuterated DPPC samples. This pressure range permitted us to explore the phase behavior of DPPC from the liquid-crystalline (LC) phase through various gel phases such as the Gel I (P beta), Gel II (L beta), Gel III, Gel X, and the interdigitated, Gel i, gel phase. Pressure had an ordering effect on all chain segments both in the LC phase and various high pressure gel phases as indicated by the increase in SCD bond order parameter and the first moment, M1, with pressure. Compared with the adjacent gel phases, the Gel i phase had the highest order. Also, in all gel phases the carbon-9 segment of the chains had the most restricted motions in contrast to the LC phase, where the carbon-2 segment was the most restricted. In the LC phase, T1 and T2 values for all segments decreased with pressure, indicative of the fast correlation time regime. Similarly, T1 decreased with pressure in the Gel I and the interdigitated Gel i gel phases but changed to the slow correlation time regime at the Gel i/Gel II phase transition. For T2, which reflects slow motions, the transition to the slow correlation time regime occurred already at LC/Gel I phase transition. Considering the various motions which contribute to relaxation, the behavior of T1 and T2 in the Gel 11 through Gel X phases showing discontinuities and slope changes at the phase transitions was, as expected, quite complex.In addition we found a straight line relationship for T-1 vs. S2D, and T-1 vs. S2CD for the deuterons in the 9 and 13 positions in the LC phase in the pressure range investigated.

Pressure effects on the physical properties of lipid bilayers detected by trans-parinaric acid fluorescence decay

The effects of hydrostatic pressure on the physical properties of large unilamellar vesicles of single lipids dipalmitoyl phosphatidylcholine (DPPC) and dimyristoyl phosphatidylcholine (DMPC) and lipid mixtures of DMPC/DPPC have been studied from time-resolved fluorescence of trans-parinaric acid. Additional experiments were carried out using diphenylhexatriene to compare the results extracted from both probes. Fluorescence decays were analyzed by the maximum entropy method. Pressure does not influence the fluorescence lifetime distribution of trans-parinaric acid in isotropic solvents. However, in pressurized lipid bilayers an abrupt change was observed in the lifetime distribution which was associated with the isothermal pressure-induced phase transition. The pressure to temperature equivalence values, dT/dP, determined from the midpoint of the phase transitions, were 24 and 14.5 degrees C kbar-1 for DMPC and POPC, respectively. Relatively moderate pressures of about 500 bar shifted the DMPC/DPPC phase diagram 11.5 degrees C to higher temperatures. The effects of pressure on the structural properties of these lipid vesicles were investigated from the anisotropy decays of both probes. Order parameters for all systems increased with pressure. In the gel phase of POPC the order parameter was smaller than that obtained in the same phase of saturated phospholipids, suggesting that an efficient packing of the POPC hydrocarbon chains is hindered.