Universal Behavior of Membranes with Sterols (original) (raw)
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Biochimica et Biophysica Acta (BBA) - Biomembranes, 1995
We report the results of a comparative study of the molecular order and dynamics of phosphatidylcholine (PC) bilayer membranes in the absence and presence of cholesterol, ergosterol and lanosterol, using deuterium (2 H) nuclear magnetic resonance (NMR) of deuterated phospholipid molecules, in addition to solid state m3C and 31P-NMR. Using dimyristoylphosphatidylcholines (DMPCs) specifically labeled at positions 2', 3', 4', 6', 8', 10' and 12' of the sn-2 chain together with the perdeuterated 2-[2HzT]DMPC derivative, the order profile for 9 of the 13 methylene groups of the sn-2 chain was established at 25°C for DMPC, DMPC/cholesterol, DMPC/ergosterol and DMPC/lanosterol membranes, at a fixed sterol/phospholipid mol ratio of 30%, and in the presence of excess water. The overall ordering effects were found to be ergosterol > cholesterol >> lanosterol. Transverse relaxation (T2c) studies of these systems indicated that while for DMPC, DMPC/cholesterol and DMPC/ergosterol the relative relaxation rates were in qualitative agreement with models which assume cooperative motions of the bilayer molecules as the main relaxation mechanism, those in DMPC/lanosterol were anomalously high, suggesting alterations of lipid packing. Using dipalmitoylphosphatidylcholine (DPPC) deuterated at the trimethylammonium group of the choline moiety, we found that the differential ordering and motional effects induced by the sterols in the acyl chains were also reflected in the headgroup, both in the gel (L~) and liquid-crystalline phases, t3C and ~H spin dynamics studies of these systems, including cross-polarization, rotating frame longitudinal relaxation and dipolar echo relaxation rates showed that the mobility of the different regions of the phospholipid molecules in the binary lipid systems were inversely correlated with the ordering effects induced by the sterols. A novel combination of C-D bond order parameters (obtained by :H-NMR) and 13C-IH cross polarization rates confirmed these results. The effects of the same sterols at the same molar proportion on the unsaturated lipid l-[2H3~]palmitoyl-2-oleoyl-snglycero-3-phosphatidylcholine (2H3:POPC) at 25 and 35°C were different from those observed on DMPC and showed ordering effects which are largest for cholesterol, while ergosterol and lanosterol produced significantly smaller effects. Transverse relaxation studies indicate that while cholesterol does not perturb cooperative motions in POPC, both ergosterol and lanosterol do. Again, high-resolution solid state J3C-NMR studies support the conclusions of the 2H-NMR experiments. Titration experiments using both 2H and13C-NMR show that ergosterol affects POPC bilayer structure up to 50 mol% but it increases the order of the phospholipid acyl chains only up to about 25 mol%. Beyond that level, it has a smaller ordering effect, possibly indicating aggregation or other more complex phase behavior. At > 30 mol% ergosterol, ~3C spectra reveal the presence of a second form of the sterol. However, 31p-NMR spectra show that all POPC/sterol systems retain a bilayer configuration up to 30 mol% sterol. The concentration of ergosterol which induces maximum order in the POPC membranes coincides with that present in the plasma membranes of the protozoan parasite To'panosoma cruzi. Taken together, our results indicate that the effects of sterols on PC bilayers are very complex, and depend on both sterol structure and on the fatty acids esterified to the phospholipid.
From Lanosterol to Cholesterol: Structural Evolution and Differential Effects on Lipid Bilayers
Biophysical Journal, 2002
Cholesterol is an important molecular component of the plasma membranes of mammalian cells. Its precursor in the sterol biosynthetic pathway, lanosterol, has been argued by Konrad Bloch (Bloch, K. 1965. Science. 150:19 -28; 1983. CRC Crit. Rev. Biochem. 14:47-92;. Blonds in Venetian Paintings, the Nine-Banded Armadillo, and Other Essays in Biochemistry. Yale University Press, New Haven, CT.) to also be a precursor in the molecular evolution of cholesterol. We present a comparative study of the effects of cholesterol and lanosterol on molecular conformational order and phase equilibria of lipid-bilayer membranes. By using deuterium NMR spectroscopy on multilamellar lipid-sterol systems in combination with Monte Carlo simulations of microscopic models of lipid-sterol interactions, we demonstrate that the evolution in the molecular chemistry from lanosterol to cholesterol is manifested in the model lipid-sterol membranes by an increase in the ability of the sterols to promote and stabilize a particular membrane phase, the liquid-ordered phase, and to induce collective order in the acyl-chain conformations of lipid molecules. We also discuss the biological relevance of our results, in particular in the context of membrane domains and rafts.
2014
We employed deuterium nuclear magnetic resonance spectroscopy (2 H-NMR) to investigate the effect of sterol structure on lipid membrane organization. Cholesterol is the major sterol component of mammalian cell plasma membranes. It strongly affects the properties of phospholipid membranes. For example, incorporating cholesterol in liquid crystalline membranes increases lipid acyl chain order, and induces the liquid ordered phase which is considered to have biological importance. We first measured the chain ordering in pure bilayers of 1-cholesterylhemisuccinoyl-2-palmitoyl(d31)-snglycero-3-phosphocholine (CholPC), a sterol-modified phospholipid with a cholesterol moiety covalently attached to the phospholipid glycerol backbone in place of one of the lipid acyl chains. We then compared CholPC's chain ordering with that of 1-palmitoyl-2palmitoyl-d31-sn-glycero-3-phosphocholine (DPPC-d31)/cholesterol and found that constrainded cholesterol's ability to order adjacent acyl chains is greatly reduced. Several sterols, broadly similar in structure to cholesterol but with specific chemical modifications, are prevalent in plant or fungal cell plasma membranes. We used 2 H-NMR to study the influence of sterol structure on its effectiveness in modifying the acyl chain order of a 1-palmitoyl(d31)-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d31) membrane. Spectra of POPC-d31 multilamellar vesicles containing campesterol, βsitosterol, brassicasterol or stigmasterol were taken at 25 o C for sterol concentrations up to 45 mol% and compared to previous observations obtained using cholesterol, 7dehydrocholesterol (7-DHC) or ergosterol. Among the sterol structural modifications we compared, the C22 double bond reduced the sterol's ordering ability the most, followed by a C24 ethyl or methyl substituent. Finally we used 2 H-NMR to study the effect of sterol structure on the propensity of sterols to induce phase separation in equimolar DPPC/POPC/sterol membranes containing 7-DHC, brassicasterol or stigmasterol. The results were compared to previous observations obtained for membranes containing cholesterol or ergosterol, which highlighted the significance of sterol structure on phase separation promoting properties. Such comparative studies are prerequisites to establishing the underlying principles of sterol/phospholipid interactions.
2007
Lateral pressure profiles have been suggested to play a significant role in many cellular membrane processes by affecting, for example, the activation of membrane proteins through changes in their conformational state. This may be the case if the lateral pressure profile is altered due to changes in molecular composition surrounding the protein. In this work, we elucidate the effect of varying sterol type on the lateral pressure profile, an issue of topical interest due to lipid rafts and their putative role for membrane protein functionality. We find that the lateral pressure profile is altered when cholesterol is replaced by either desmosterol, 7-dehydrocholesterol, or ketosterol. The observed changes in the lateral pressure profile are notable and important since desmosterol and 7-dehydrocholesterol are the immediate precursors of cholesterol along its biosynthetic pathway. The results show that the lateral pressure profile and the resulting elastic behavior of lipid membranes are sensitive to the sterol type, and support a mechanism where changes in protein conformational state are facilitated by changes in the lateral pressure profile. From a structural point of view, the results provide compelling evidence that despite seemingly minor differences, sterols are characterized by structural specificity.
Chemistry and Physics of Lipids, 2010
This review deals with the effect of variations in phospholipid and sterol structure on the nature and magnitude of lipid-sterol interactions in lipid bilayer model membranes. The first portion of the review covers the effect of Chol itself on the thermotropic phase behavior and organization of a variety of different glycero-and sphingolipid membrane lipid classes, varying in the structure and charge of their polar headgroups and in the length and structure of their fatty acyl chains. The second part of this review deals with the effect of variations in sterol structure on the thermotropic phase behavior and organization primarily of the well studied DPPC model membrane system. In the third section, we focus on some of the contributions of sterol functional group chemistry, molecular conformation and dynamics, to sterollipid interactions. Using those studies, we re-examine the results of recently published experimental and computer-modeling studies to provide a new more dynamic molecular interpretation of sterol-lipid interactions. We suggest that the established view of the rigid sterol ring system and extended alkyl side-chain obtained from physical studies of cholesterol-phospholipid mixtures may not apply in lipid mixtures differing in their sterol chemical structure. L is lauroyl, M is myristoyl, P is palmitoyl, S is stearoyl, A is arachidoyl, E is elaidoyl and O is oleoyl (DMPC is dimyristoylphosphatidylcholine, etc.); LC , lamellar crystalline phase with tilted hydrocarbon chains; L  or L  , planar lamellar gel state with tilted or untilted hydrocarbon chains, respectively; P  , rippled gel state with titled hydrocarbon chains; L␣, lamellar liquid-crystalline state; Lo or L d , lamellar liquid-ordered or liquid-disordered state, respectively; Tp and Tm, the pretransition and main phase transition temperature, respectively; Hp and Hm, enthalpy of the pretransition and main phase transition, respectively; T 1/2 , width of the DSC endotherm at half height ( • C), which is inversely related to the cooperativity of the phase transition; Tm shp , phase transition temperature of the sharp component of the DSC endotherm corresponding to the sterol-poor bilayer regions; Tm brd , phase transition temperature of the broad component of the DSC endotherm corresponding to the sterol-rich bilayer regions; Hm shp , phase transition enthalpy of the sharp component of the DSC endotherm corresponding to the sterol-poor bilayer regions; Hm brd , phase transition enthalpy of the broad component of the DSC endotherm corresponding to the sterol-rich bilayer regions; DSC, differential scanning calorimetry; FTIR, Fourier transform infrared; NMR, nuclear magnetic resonance.
Interactions of cholesterol with the membrane lipid matrix. A solid state NMR approach
Biochimie, 1991
The effects of cholesterol on the structure and dynamics of dimyristoylphosphatidylcholine (DMPC) model membranes have been monitored as functions of temperature and cholesterol concentration in the membrane. The use of deuterium labels both on the cholesterol fused ring system and on the lipid chains in conjunction with solid state deuterium nuclear magnetic resonance (2H-NMR) afforded to monitor the degree of ordering of both molecules in a mixed system. The degree of ordering of the lipid head group was followed by phosphorus-31 (31p)-NMR. New findings on the effect of cholesterol on DMPC may be summarized as follows: i) cholesterol disorders the lipid chains below temperature of the DMPC gel-to-fluid transition (To) and orders them above; the effect is linear with cholesterol concentration at 0 and 60°C but for intermediate temperatures, a saturation effect is observed at 20-30 mol %; ii) the ordering-disordering effects are perceived similarly by all chain segments with, however, a greater sensitivity for positions near the bilayer center; iii) below To, the lipid head group is considerabily disordered by increasing amounts of cholesterol but slightly affected above; iv) the degree of ordering of cholesterol is quasi temperature independent for fractions greater than or equal to 30%; v) the average orientation of the cholesterol rigid body is perpendicular to the bilayer surface and exhibits little variations with temperature and cholesterol concentration. Variations in membrane dynamics are interpreted in terms of cholesterol-induced changes in bilayer thickness. The sterol is described as a regulator of membrane dynamics (for fractions greater than or equal to 30%) by providing the bilayer with quasi constant motional amplitudes over a large temperature scale.
2020
Cholesterol and ergosterol are two dominant sterols in the membranes of eukaryotic and yeast cells, respectively. Although their chemical structure is very similar, their impact on the structure and dynamics of membranes differs. In this work, we have explored the effect of these two sterols on binary mixtures with 1,2-dipalnitoyl-sn-glycerol-3-phosphocholine (DPPC) lipid bilayer at various sterol concentration and temperatures, employing molecular dynamics simulations. The simulations revealed that cholesterol has a stronger impact on the ordering of the lipid chains and leads to more condensed membranes with respect to ergosterol. This difference likely arises from a more planar structure of the ring part as well as the better alignment of cholesterol among the DPPC chains with respect to ergosterol. The degree of the planarity of the ring system affects the orientation of the methyl groups on the rough side and distribute the lipid chains on the two sides of the sterols different...
Organization and interaction of cholesterol and phosphatidylcholine in model bilayer membranes
Biochemistry, 1990
The molecular organization of sterols in liposomes of 1 -palmitoyl-2-oleoyl-sn-glycero-3phosphocholine (POPC) at 37 OC is examined by utilizing the fluorescent analogue of cholesterol cholesta-5,7,9-trien-3/3-01 (cholestatrienol). (1) Cholestatrienol is shown to be indistinguishable from native cholesterol in terms of its ability to condense POPC, as determined by (i) pressure/area studies of mixed-lipid monolayers and (ii) its ability to increase the order of POPC bilayers (determined by electron spin resonance studies) whether on its own or admixed with cholesterol at various ratios. (2) By analysis of the perturbation of the absorption spectra, cholestatrienol was found to be freely miscible in aggregates of cholesterol in buffer.
Morphology and dynamics of domains in ergosterol or cholesterol containing membranes
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2019
The effect of cholesterol and ergosterol on supported lipid bilayers composed of 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and egg sphingomyelin (eSM) in a 1/1 M ratio was studied using atomic force microscopy. The addition of ergosterol or cholesterol to these membranes considerably modifies both the structure and the dynamics of the domains present in them. The height of the eSM enriched domains increases with concentration of both sterols, but more markedly with ergosterol. The height of the POPC enriched domains increases with concentration in a similar manner for both sterols. This effect is larger for eSM than for POPC when ergosterol, not cholesterol, is present. Domain coverage increases with both sterols at 5 mol% but decreases at 20 mol% and almost disappears at 40 mol%. The size of the eSM enriched domains decreases with sterol concentration, more markedly with cholesterol. Bilayer rupture forces show that overall stiffness increases with the addition of 5 mol% cholesterol, but only for the eSM enriched domains with ergosterol at the same concentration. At larger sterol concentrations the stiffness of both regions becomes reduced. At 40 mol% sterol concentration, both membranes present the same rupture force value. To gain mechanistic insight into these observations we performed Quantum Mechanical calculations and Molecular Dynamics simulations of the sterol molecules. We found that conformational freedom for the sterol molecules is quite different. This difference might be behind the observed phenomena. Finally, the different action of sterols on membrane properties is related to the sterol-dependent ionophoretic activity of polyene antibiotics.