Effect of protein hydration on receptor conformation: decreased levels of bound water promote metarhodopsin II formation.

Neutral solutes were used to investigate the effects of osmotic stress both on the ability of rhodopsin to undergo its activating conformation change and on acyl chain packing in the rod outer segment (ROS) disk membrane. The equilibrium concentration of metarhodopsin II (MII), the conformation of photoactivated rhodopsin, which binds and activates transducin, was increased by glycerol, sucrose, and stachyose in a manner which was linear with osmolality. Analysis of this shift in equilibrium in terms of the dependence of ln(Keq) on osmolality revealed that 20 +/- 1 water molecules are released during the MI-to-MII transition at 20 degrees C, and at 35 degrees C 13 +/- 1 waters are released. At 35 degrees C the average time constant for MII formation was increased from 1.20 +/- 0.09 ms to 1.63 +/- 0.09 ms by addition of 1 osmolal sucrose or glycerol. The effect of the neutral solutes on acyl chain packing in the ROS disk membrane was assessed via measurements of the fluorescence lifetime and anisotropy decay of 1,6-diphenyl-1,3,5-hexatriene (DPH). Analysis of the anisotropy decay of DPH in terms of the rotational diffusion model showed that the angular width of the equilibrium orientational distribution of DPH about the membrane normal was progressively narrowed by increased osmolality. The parameter fv, which is proportional to the overlap between the DPH orientational probability distribution and a random orientational distribution, was reduced by the osmolytes in a manner which was linear with osmolality. This study highlights the potentially opposing interplay between the effect of membrane surface hydration on both the lipid bilayer and integral membrane protein structure. Our results further demonstrate that the binding and release of water molecules play an important role in modulating functional conformational changes for integral membrane proteins, as well as for soluble globular proteins.     

Phospholipid spin probes measure the effects of ethanol on the molecular order of liver microsomes

Ethanol, in vitro, is known to perturb the molecular order of the phospholipids in biological membranes, while chronic ethanol exposure, in vivo, leads to resistance to disordering. Such changes have usually been measured by electron spin resonance, utilizing fatty acid spin probes. The use of such probes is controversial, since their orientation in the membrane may not accurately represent that of individual phospholipids. We, therefore, compared ethanol-induced structural perturbations in the membranes of rat hepatic microsomes measured with the spin probe 12-doxylstearic acid (SA 12) with those assayed with various phospholipid spin probes. With SA 12, the addition of increasing amounts of ethanol (50-250 mM) in vitro caused a progressive decrease in the membrane molecular order, as measured by electron spin resonance (ESR). By contrast, microsomes obtained from rats chronically fed ethanol were resistant to the disordering effect of ethanol. Microsomes labeled with the phospholipid spin probes 1-palmitoyl-2-(12-doxylstearoyl)phosphatidylcholine, -phosphatidylethanolamine, or -phosphatidic acid also exhibited increased disordering with the addition of increasing amounts of ethanol. However, the effect noted with phospholipid spin probes was less than that observed with the fatty acid probe. Microsomes obtained from the livers of chronically intoxicated animals labeled with the phospholipid probes were also resistant to the disordering effects of ethanol in vitro. These results suggest that fatty acid spin probes are qualitatively valid for measuring membrane perturbations in biological membranes, ethanol affects all microsomal phospholipids, regardless of chemical dissimilarities (e.g., head-group structure), in a qualitatively similar fashion, and the fluidization of fatty acyl chains in microsomal membranes is comparable in different membrane phospholipids.     

Quantifying the differential effects of DHA and DPA on the early events in visual signal transduction

A range of evidence from animal, clinical and epidemiological studies indicates that highly polyunsaturated acyl chains play important roles in development, cognition, vision and other aspects of neurological function. In a number of these studies n3 polyunsaturated fatty acids (PUFAs) appear to be more efficacious than n6 PUFAs. In a previous study of retinal rod outer segments obtained from rats raised on either an n3 adequate or deficient diet, we demonstrated that the replacement of 22:6n3 by 22:5n6 in the n3 deficient rats led to functional deficits in each step in the visual signaling process (Niu et al., 2004). In this study, we examined rhodopsin and phosphodiesterase function and acyl chain packing properties in membranes consisting of phosphatidylcholines with sn-1=18:0, and sn-2=22:6n3, 22:5n6, or 22:5n3 in order to determine if differences in function are due to the loss of one double bond or due to differences in double bond location. At 37 °C the n6 lipid shifted the equilibrium between the active metarhodopsin II (MII) state and inactive metarhodopsin I (MI) state towards MI. In addition, 22:5n6 reduced the rates of MII formation and MII-transducin complex formation by 2- and 6-fold, respectively. At a physiologically relevant level of rhodopsin light stimulation, the activity of phosphodiesterase was reduced by 50% in the 22:5n6 membrane, relative to either of the n3 membranes. Activity levels in the two n3 membranes were essentially identical. Ensemble acyl chain order was assessed with time-resolved fluorescence measurements of the membrane probe diphenylhexatriene (DPH). Analysis in terms of the orientational distribution of DPH showed that acyl chain packing in the two n3 membranes is quite similar, while in the 22:5n6 membrane there was considerably less packing disorder in the bilayer midplane. These results demonstrate that the n3 bond configuration uniquely optimizes the early steps in signaling via a mechanism which may involve acyl chain packing deep in the bilayer.     

Manipulation of cholesterol levels in rod disk membranes by methyl-beta-cyclodextrin: effects on receptor activation

The effect of cholesterol on rod outer segment disk membrane structure and rhodopsin activation was investigated. Disk membranes with varying cholesterol concentrations were prepared using methyl-beta-cyclodextrin as a cholesterol donor or acceptor. Cholesterol exchange followed a simple equilibrium partitioning model with a partition coefficient of 5.2 +/- 0.8 in favor of the disk membrane. Reduced cholesterol in disk membranes resulted in a higher proportion of photolyzed rhodopsin being converted to the G protein-activating metarhodopsin II (MII) conformation, whereas enrichment of cholesterol reduced the extent of MII formation. Time-resolved fluorescence anisotropy measurements using 1,6-diphenyl-1,3,5-hexatriene showed that increasing cholesterol reduced membrane acyl chain packing free volume as characterized by the parameter f(v). The level of MII formed showed a positive linear correlation with f(v) over the range of 4 to 38 mol % cholesterol. In addition, the thermal stability of rhodopsin increased with mol % of cholesterol in disk membranes. No evidence was observed for the direct interaction of cholesterol with rhodopsin in either its agonist- or antagonist-bound form. These results indicate that cholesterol mediates the function of the G protein-coupled receptor, rhodopsin, by influencing membrane lipid properties, i.e. reducing acyl chain packing free volume, rather than interacting specifically with rhodopsin.     

Ethanol effects on binary and ternary supported lipid bilayers with gel/fluid domains and lipid rafts

Ethanol-lipid bilayer interactions have been a recurrent theme in membrane biophysics, due to their contribution to the understanding of membrane structure and dynamics. The main purpose of this study was to assess the interplay between membrane lateral heterogeneity and ethanol effects. This was achieved by in situ atomic force microscopy, following the changes induced by sequential ethanol additions on supported lipid bilayers formed in the absence of alcohol. Binary phospholipid mixtures with a single gel phase, dipalmitoylphosphatidylcholine (DPPC)/cholesterol, gel/fluid phase coexistence DPPC/dioleoylphosphatidylcholine (DOPC), and ternary lipid mixtures containing cholesterol, mimicking lipid rafts (DOPC/DPPC/cholesterol and DOPC/sphingomyelin/cholesterol), i.e., with liquid ordered/liquid disordered (ld/lo) phase separation, were investigated. For all compositions studied, and in two different solid supports, mica and silicon, domain formation or rearrangement accompanied by lipid bilayer thinning and expansion was observed. In the case of gel/fluid coexistence, low ethanol concentrations lead to a marked thinning of the fluid but not of the gel domains. In the case of ld/lo all the bilayer thins simultaneously by a similar extent. In both cases, only the more disordered phase expanded significantly, indicating that ethanol increases the proportion of disordered domains. Water/bilayer interfacial tension variation and freezing point depression, inducing acyl chain disordering (including opening and looping), tilting, and interdigitation, are probably the main cause for the observed changes. The results presented herein demonstrate that ethanol influences the bilayer properties according to membrane lateral organization.     

Effects of cholesterol on conformational disorder in dipalmitoylphosphatidylcholine bilayers. A quantitative IR study of the depth dependence

A method originally proposed by Snyder and Poore [(1973) Macromolecules 6, 708-715] as a specific probe of trans-gauche isomerization in hydrocarbon chains and recently applied [Mendelsohn et al. (1989) Biochemistry 28, 8934-8939] to the quantitative determination of phospholipid acyl chain conformational order is utilized to monitor the effects of cholesterol at various depths in dipalmitoylphosphatidylcholine (DPPC) bilayers. The method is based on the observation that the CD2 rocking modes from the acyl chains of specifically deuterated phospholipids occur at frequencies in the Fourier transform infrared spectrum which depend upon the local geometry (trans or gauche) of the C-C-C skeleton surrounding a central CD2 group. Three specifically deuterated derivatives of DPPC, namely, 4,4,4',4'-d4 DPPC (4-d4 DPPC), 6,6,6',6'-d4 DPPC (6-d4 DPPC), and 12,12,12',12'-d4 DPPC (12-d4 DPPC), have been synthesized, and the effects of cholesterol addition at 2:1 DPPC/cholesterol (mol:mol) on acyl chain order at various temperatures have been determined. At 48 degrees C, cholesterol inhibits gauche rotamer formation by factors of approximately 9 and approximately 6 at positions 6 and 4, respectively, of the acyl chains, thus demonstrating a strong ordering effect in regions of the bilayer where the sterol rings are presumed to insert parallel to the DPPC acyl chains. In contrast, the ability of the sterol to order the acyl chains is much reduced at the 12-position. The sterol demonstrates only a slight disordering of phospholipid gel phases. Finally, the contributions of different classes of gauche conformers to the spectra have been determined.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dependence with nutritional status of the ethanol effects on fatty acid metabolism in rat hepatocytes

1. The effects of ethanol on fatty acid synthesis, esterification and oxidation were studied in hepatocytes isolated from fed and 24 hr fasted rats. 2. [3H]H2O was preferentially incorporated into the glycerol backbone of triglycerides and phospholipids. Addition of ethanol markedly increased the incorporation of this label in both classes of glycerolipids; the increase was higher in fasted rat hepatocytes, both in the glycerol backbone and acyl groups of glycerolipids. 3. Ethanol increased [U-14C]palmitate incorporation into triglycerides only in hepatocytes from fasted rats. 4. [14C]CO2 and total acid soluble product formation from [1-14C]palmitate resulted inhibited by ethanol both in the fed and the fasted state.     

Interaction of ethanol with biological membranes

Ethanol is among the drugs with anesthetic potency determined by lipid solubility, in accord with the Meyer-Overton hypothesis. Thus, it is likely that ethanol acts in a hydrophobic environment. Using electron paramagnetic resonance with 5-doxylstearic acid as spin label, we find that ethanol disorders mouse cell membranes, making the lipid matrix more fluid. We surmise that consequent disruption of the function of integral membrane proteins may be the cause of ethanol's central actions. When mice are treated for 8 days with ethanol, their membranes become tolerant to the disordering effect of ethanol. This tolerance is accompanied by an increased proportion of cholesterol in the membranes.     

Molecular blending by polymerization of intercalated solvent. Poly(gamma-benzyl-L-glutamate)/benzyl methacrylate as a model system

The aim of the present research is to obtain blending between a polymer and a (polymerized) solvent on the molecular level. Because of its rigid rod structure, poly(gamma-benzyl-L-glutamate) (PBLG) is chosen as the polymer. Benzyl methacrylate (BzMA) has been chosen as the solvent for two reasons. First, the structure of the solvent is very similar to the structure of the side chain of PBLG, favoring interactions between the two materials. Second, the solvent can be polymerized, because of the presence of a C=C bond. In cast films of PBLG and BzMA separate zones of the polymer and solvent are present. Wide-angle X-ray diffraction and Raman results show that upon heating the cast films homogenization occurs and solvent molecules intercalate between the helices of PBLG. At 150 degrees C a hexagonal packing is obtained. The dimensions of the obtained packing depend on the solvent concentration, which confirms that solvent molecules are indeed present within the crystalline lattice. DSC experiments imply that the observed changes upon heating correspond to thermodynamic processes. On cooling the homogeneous samples, disordering of the hexagonal packing occurs. Polymerization of the homogeneous samples results in a disordering of the hexagonal packing and in a contraction of the unit cell. The latter once more confirms that solvent molecules are indeed present within the crystalline lattice. The applied principle of polymerization of a solvent in a molecular homogeneous system can be favorable for many applications, for which morphology control at the molecular level is required.     

Resistance to ethanol disordering of membranes from ethanol-fed rats is conferred by all phospholipid classes.

Phospholipids extracted from liver microsomes and mitochondria of ethanol-fed rats retained the resistance to membrane disordered by ethanol which is observed in the intact isolated membranes. The lipid extracts were separated into the major phospholipid classes (phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol from microsomes and phosphatidylcholine, phosphatidylethanolamine and cardiolipin from mitochondria) by preparative TLC. The extent of membrane disordering by ethanol of phospholipid vesicles composed of a mixture of phospholipids from ethanol-fed rats and controls was determined from the reduction of the order parameter of the spin-probe 12-doxyl-stearate. In contrast to previous reports, we found that all phospholipid classes from ethanol-fed rats confer resistance to disordering by ethanol. To a first approximation the extent of resistance was proportional to the fraction of lipids from ethanol-fed rats, regardless of the phospholipid head-group. Subtle differences between phospholipid classes may exist but were too small to measure accurately. Except for phosphatidylethanol, incorporation of anionic phospholipids did not have a significant effect on the sensitivity of phospholipid vesicles to the disordering effect of ethanol. Vesicles prepared from mixtures of various dioleoyl phospholipids and natural phospholipids did not indicate a clear effect of fatty acid saturation on the sensitivity to disordering by ethanol. Although the precise molecular changes that occur in phospholipids from ethanol-fed rats have not been fully characterized it appears that subtle changes in all phospholipid classes contribute to the resistance to ethanol disordering of these membranes.     

Nitroxide spin-probe study of amphotericin B-ergosterol interaction in egg phosphatidylcholine multilayers

The interaction between the polyene macrolide antibiotic, amphotericin B, and ergosterol in egg phosphatidylcholine multilayers was investigated using head group and acyl chain nitroxide spin-labelled phosphatidylcholine as probes. At physiological concentrations of less than 15 mol% sterol in egg phosphatidylcholine multilayers amphotericin B accumulates near the head group region until an amphotericin B : ergosterol ratio of approximately 0.7 is achieved. As the proportion of amphotericin B is increased above this value, formation of an acyl chain disordering complex occurs which has an approximate antibiotic:sterol ratio of unity. Dicetyl phosphate was used to increase the solubility of ergosterol past its normal limit in pure egg phosphatidylcholine (approximately 15 mol%). At concentrations of ergosterol higher than 15 mol% a complex of two ergosterol molecules and one amphotericin B was postulated when there was insufficient antibiotic to form a 1:1 complex.     

The presence of ethanol in the oviductal and uterine luminal fluids of alcoholized rats

Blood ethanol level and the presence of ethanol in the oviductal and uterine luminal fluids were determined in female albino rats (Wistar strain) following chronic alcoholization by 20% ethanol offered ad libitum in drinking water during a period of 40-50 and 90-100 days, respectively. Ethanol was found both in the oviductal and in the uterine luminal fluids in lower concentrations as compared with the blood ethanol level. The findings presented suggest the possible direct noxious action of ethanol upon preimplantation development (effects detected in previous investigations). Problems raised by present results are discussed.     

Regulation of membrane proteins by dietary lipids: effects of cholesterol and docosahexaenoic acid acyl chain-containing phospholipids on rhodopsin stability and function

Purified bovine rhodopsin was reconstituted into vesicles consisting of 1-stearoyl-2-oleoyl phosphatidylcholine or 1-stearoyl-2-docosahexaenoyl phosphatidylcholine with and without 30 mol % cholesterol. Rhodopsin stability was examined using differential scanning calorimetry (DSC). The thermal unfolding transition temperature (T_m) of rhodopsin was scan rate-dependent, demonstrating the presence of a rate-limited component of denaturation. The activation energy of this kinetically controlled process (E_a) was determined from DSC thermograms by four separate methods. Both T_m and E_a varied with bilayer composition. Cholesterol increased the T_m both the presence and absence of docosahexaenoic acid acyl chains (DHA). In contrast, cholesterol lowered E_a in the absence of DHA, but raised E_a in the presence of 20 mol % DHA-containing phospholipid. The relative acyl chain packing order was determined from measurements of diphenylhexatriene fluorescence anisotropy decay. The T_m for thermal unfolding was inversely related to acyl chain packing order. Rhodopsin kinetic stability (E_a) was reduced in highly ordered or disordered membranes. Maximal kinetic stability was found within the range of acyl chain order found in native bovine rod outer segment disk membranes. The results demonstrate that membrane composition has distinct effects on the thermal versus kinetic stabilities of membrane proteins, and suggests that a balance between membrane constituents with opposite effects on acyl chain packing, such as DHA and cholesterol, may be required for maximum protein stability.     

Metabolic changes of membrane lipid composition in Acholeplasma laidlawii by hydrocarbons, alcohols, and detergents: arguments for effects on lipid packing

The packing of lipids into different aggregates, such as spheres, rods, or bilayers, is dependent on the hydrophobic volume, the hydrocarbon-water interfacial area, and the hydrocarbon chain length of the participating molecules, according to the self-assembly theory [Israelachvili, J. N., Marcelja, S., & Horn, R. G. (1980) Q. Rev. Biophys. 13, 121-200]. The origin of the participating molecules should be of no importance with respect to their abilities to affect the above-mentioned parameters. In this investigation, Acholeplasma laidlawii, with a defined acyl chain composition of the membrane lipids, has been grown in the presence of three different classes of foreign molecules, known to partition into model and biological membranes. This results in an extensive metabolic alteration in the lipid polar head group composition, which is expressed as changes in the molar ratio between the lipids monoglucosyldiglyceride (MGDG) and diglucosyldiglyceride (DGDG), forming reversed hexagonal and lamellar phases in excess water, respectively. The formation of nonlamellar phases by A. laidlawii lipids depends critically upon the MGDG concentration [Lindblom, G., Brentel, I., Sj?lund, M., Wikander, G., & Wieslander, A. (1986) Biochemistry (preceding paper in this issue)]. The foreign molecules tested belong to the following groups: nonpolar organic solvents, alcohols, and detergents. Their effects on the gel to liquid crystalline phase transition temperature (Tm), on the order parameter of the acyl chains, and on the phase equilibria between lamellar and nonlamellar liquid crystalline phases in lipid-water model systems are known in several instances.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of ethanol on the activity of brain enzymes

Ethanol alters, in a selective manner, the activity of several membrane-bound enzymes in the central nervous system (CNS) which are important for neuronal transmission of information. Ethanol inhibits Na+/K+-transporting ATPase activity, while adenylate cyclase (AC) activity is stimulated by ethanol added in vitro. Ethanol's effects on AC activity are mediated primarily via effects on proteins that regulate AC activity. Ethanol has selective effects on monoamine oxidase activity, in that the B form of the enzyme is more sensitive to inhibition by ethanol added in vitro. The selective effects of ethanol on different membrane-bound CNS enzymes may result from differing membrane lipid microenvironments of the enzymes, or from differences in the enzyme proteins per se.     

Differential effects of ethanol and hexanol on the Escherichia coli cell envelope.

Both ethanol and hexanol inhibited the growth of Escherichia coli, but their effects on the organization and composition of the cell envelope were quite different. Hexanol (7.8 x 10(-3) mM) increased membrane fluidity, whereas ethanol (0.67 M) had little effect. During growth in the presence of ethanol, the proportion of unsaturated fatty acids increased. The opposite change was induced by hexanol. Unlike hexanol, growth in the presence of ethanol resulted in the production of un-cross-linked peptidoglycan with subsequent lysis. Salt (0.3 M) protected cells against ethanol-induced lysis but potentiated growth inhibition by hexanol. Mutants isolated for resistance to ethanol-induced lysis synthesized cross-linked peptidoglycan during growth in the presence of ethanol but remained sensitive to hexanol. A general hypothesis was presented to explain the differential effects of ethanol and hexanol. All alcohols are viewed as similar in having both an apolar chain capable of interacting with hydrophobic environments and a hydroxyl function capable of hydrogen bonding. The differential effects of short-chain alcohols may represent effects due to the high molar concentrations of hydrogen bonding groups with an apolar end within the environment. These may replace bound water in some cases. With longer-chain alcohols such as hexanol, the effects of the acyl chain would dominate, and limitations of solubility and cellular integrity would mask these hydroxyl effects.     

Nuclear Overhauser enhancement spectroscopy cross-relaxation rates and ethanol distribution across membranes

Measurement of nuclear Overhauser enhancement spectroscopy cross-relaxation rates between ethanol and palmitoyloleoylphosphatidylcholine bilayers was combined with atomic-level molecular dynamics simulations. The molecular dynamics trajectories yielded autocorrelation functions of proton dipole-dipole interactions, and, consequently, relaxation times and cross-relaxation rates. These analyses allow the measured cross-relaxation rates to be interpreted in terms of relative interaction strengths with the various segments of the lipid molecule. We determined that cross-relaxation between ethanol and specific lipid resonances is primarily determined by the sites of interaction with some modulation due to lipid disorder and to local differences in intramolecular lipid dynamics. The rates scale linearly with the lifetime of temporary ethanol-lipid associations. Ethanol interacts with palmitoyloleoylphosphatidylcholine bilayers primarily via hydrophilic interactions, in particular the formation of hydrogen bonds to the lipid phosphate group. There is a weak contribution to binding from hydrophobic interaction with lipid chain segments near the glycerol. However, the strength of hydrophobic interactions is insufficient to compensate for the energetic loss of locating ethanol in an exclusively hydrophobic environment, resulting in a probability of locating ethanol in the bilayer center that is three orders of magnitude lower than locating ethanol at the lipid/water interface. The low cross-relaxation rates between terminal methyl protons of hydrocarbon chains and ethanol are as much the result of infrequent chain upturns as of brief excursions of ethanol into the region of lipid hydrocarbon chains near the glycerol. The combination of nuclear magnetic resonance measurements and molecular dynamics simulations offers a general pathway to study the interaction of small molecules with the lipid matrix at atomic resolution.     

Regulation of fatty acid composition in Escherichia coli: a proposed common mechanism for changes induced by ethanol, chaotropic agents, and a reduction of growth temperature.

Growth of Escherichia coli in the presence of ethanol and chaotropic salts resulted in the synthesis of lipids containing elevated levels of unsaturated fatty acids analogous to the effect of a reduction in growth temperature. Both ethanol and chaotropic agents acted at the level of fatty acid biosynthesis and altered lipid composition by decreasing the proportion of saturated acyl chains available for the synthesis of phospholipids. A reduction in temperature causes similar effects on fatty acid biosynthesis in vivo and in vitro. Ethanol, chaotropic salts, and a decrease in temperature all weaken hydrophobic interactions. Antichaotropic salts antagonized and effects of these treatments on fatty acid synthesis in vitro. These results are consistent with a common mechanism for the effects of chaotropic agents, temperature, and ethanol on fatty acid synthesis. The biosynthesis of saturated and unsaturated acyl chains may be regulated by the strength of hydrophobic interactions. Changes in the strength of hydrophobic interactions could alter enzyme structure, substrate structure, or the equilibrium between the soluble enzymes of fatty acid synthesis and their respective acyl carrier protein substrates.     

Effects of ethanol on the development of Drosophila melanogaster: Comparison of two geographic populations

The effects of ethanol upon the development of two strains of D. melanogaster (France and tropical Africa) were studied using two different methods; either the feeding medium containing ethanol was not renewed, or it was changed daily to keep the concentration stable. Toxic effects were much more obvious with the stabilized concentration. The difference in tolerance, already known for the adults of the two populations, was also observed for larvae; the French strain was much more tolerant. Ethanol slowed down larval development but adult weight at emergence could be increased. Lipid content of adults was increased by larval ethanol feeding while water content decreased. Two populations did not react exactly in the same way and an interaction was observed between genotype and experimental technique. The results should help to clarify the role of alcoholic fermentation upon D. melanogaster under natural conditions.     

Influence of chain length and unsaturation on sphingomyelin bilayers

Sphingomyelins (SMs) are among the most common phospholipid components of plasma membranes, usually constituting a mixture of several molecular species with various fatty acyl chain moieties. In this work, we utilize atomistic molecular dynamics simulations to study the differences in structural and dynamical properties of bilayers comprised of the most common natural SM species. Keeping the sphingosine moiety unchanged, we vary the amide bonded acyl chain from 16 to 24 carbons in length and examine the effect of unsaturation by comparing lipids with saturated and monounsaturated chains. As for structural properties, we find a slight decrease in average area per lipid and a clear linear increase in bilayer thickness with increasing acyl chain length both in saturated and unsaturated systems. Increasing the acyl chain length is found to further the interdigitation across the bilayer center. This is related to the dynamics of SM molecules, as the lateral diffusion rates decrease slightly for an increasing acyl chain length. Interdigitation also plays a role in interleaflet friction, which is stronger for unsaturated chains. The effect of the cis double bond is most significant on the local order parameters and rotation rates of the chains, though unsaturation shows global effects on overall lipid packing and dynamics as well. Regarding hydrogen bonding or properties related to the lipid/water interface region, no significant effects were observed due to varying chain length or unsaturation. The significance of the findings presented is discussed.