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Schematically depicted polymorphism of phospholipid aggregates. Aggregated forms with appropriate shapes of phospholipid molecules: (A) spherical micelle, (B) cylinder, (C) bilayer, (D) inverted cylinder, and (E) inverted micelle.
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... curvature of different monolayer and bilayer lipid structures ( Fig. 1) depends to a great extent on the intrinsic shape of the phospholipid mole- cules, which in turn depends on the temperature, degree of hydration, presence of specific enzymes, pH, etc. [10]. Author's personal ...
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... lipid bilayers are formed preferentially, when the lipid molecules have cylindrical shapes (Fig. 1C), whereas cylindrical monolayers are formed when the lipid molecules are wedge shaped (as depicted in Fig. 1B and D). Conical and inverted conical shapes of lipids favor spherical (Fig. 1A) and inverted spherical (Fig. 1E) micellar shapes, respectively (see also Ref. ...
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... lipid bilayers are formed preferentially, when the lipid molecules have cylindrical shapes (Fig. 1C), whereas cylindrical monolayers are formed when the lipid molecules are wedge shaped (as depicted in Fig. 1B and D). Conical and inverted conical shapes of lipids favor spherical (Fig. 1A) and inverted spherical (Fig. 1E) micellar shapes, respectively (see also Ref. ...
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... lipid bilayers are formed preferentially, when the lipid molecules have cylindrical shapes (Fig. 1C), whereas cylindrical monolayers are formed when the lipid molecules are wedge shaped (as depicted in Fig. 1B and D). Conical and inverted conical shapes of lipids favor spherical (Fig. 1A) and inverted spherical (Fig. 1E) micellar shapes, respectively (see also Ref. ...
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... lipid bilayers are formed preferentially, when the lipid molecules have cylindrical shapes (Fig. 1C), whereas cylindrical monolayers are formed when the lipid molecules are wedge shaped (as depicted in Fig. 1B and D). Conical and inverted conical shapes of lipids favor spherical (Fig. 1A) and inverted spherical (Fig. 1E) micellar shapes, respectively (see also Ref. ...
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... the curvature of membranes depends on the intrinsic shape of the phospholipid molecules (see Fig. 1). Hence noncylindrically shaped phos- pholipids self-assemble in aqueous solutions in nonplanar structures. The tendency to curve the shape of the monolayer without any external torques and forces is called the spontaneous (intrinsic) curvature [10]. The definition of the principal intrinsic curvatures that define the intrinsic shape ...
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... curvatures are equal (C 1m ¼ C 2m ), the membrane constituents are isotropic (Fig. 4). Isotropic constituents with zero intrinsic curvatures (C 1m ¼ C 2m ¼ 0) will tend to form planar mono- layers, while the constituents having inverted conical shape (C 1m ¼ 0, C 2m < 0) will favor the formation of an inverted hexagonal structure [11] (see also Fig. 1). The intrinsic principal curvatures account for the geometrical Anisotropic ...
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... explain the effect of individual contributions to the free energy, we first determine the equilibrium configuration obtained by minimization of the bending energy alone (first two terms in Eq. (58)). There are three different geometries compared in Fig. 11: planar (corresponding to lamellar L a phase), spherical (corresponding to inverted micellar M II phase), and cylin- drical (corresponding to inverted hexagonal H II phase), see also Fig. 1. Figure 11 shows the equilibrium bending energy per lipid molecule depen- dent on the mean intrinsic curvature H m for anisotropic molecules, for ...
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... configuration obtained by minimization of the bending energy alone (first two terms in Eq. (58)). There are three different geometries compared in Fig. 11: planar (corresponding to lamellar L a phase), spherical (corresponding to inverted micellar M II phase), and cylin- drical (corresponding to inverted hexagonal H II phase), see also Fig. 1. Figure 11 shows the equilibrium bending energy per lipid molecule depen- dent on the mean intrinsic curvature H m for anisotropic molecules, for which jH m j ¼ D m (panel A) and isotropic molecules, for which D m ¼ 0 (panel B). For small jH m j ¼ D m , the bending energy increases with increasing jH m j in all three geometries (panel ...
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... explain the effect of individual contributions to the free energy, we first determine the equilibrium configuration obtained by minimization of the bending energy alone (first two terms in Eq. (58)). There are three different geometries compared in Fig. 11: planar (corresponding to lamellar L a phase), spherical (corresponding to inverted micellar M II phase), and cylin- drical (corresponding to inverted hexagonal H II phase), see also Fig. 1. Figure 11 shows the equilibrium bending energy per lipid molecule depen- dent on the mean intrinsic curvature H m for anisotropic molecules, for which jH m j ¼ D m (panel A) and isotropic molecules, for which D m ¼ 0 (panel B). For small jH m j ¼ D m , the bending energy increases with increasing jH m j in all three geometries (panel A). ...
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... favorable. Summing up, for small jH m j ¼ D m , the M II phase has the lowest bending energy, while at larger jH m j ¼ D m , the H II phase becomes the most favorable due to the average orientational ordering of phospholipid molecules. The effect is stronger for higher values of ~ k describing the direct interaction between phospholipid tails (Fig. 11A). Figure 11B shows that for isotropic molecules (having D m ¼ 0, i.e., C 1m ¼ C 2m , see also Fig. 2), the M II phase is always favored, that is, the calculated energy per lipid F b /n 0 A in the M II phase is equal to the reference value and is the smallest comparing to the energy of the L a and the H II phase. We note that for ...
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... effect is stronger for higher values of ~ k describing the direct interaction between phospholipid tails (Fig. 11A). Figure 11B shows that for isotropic molecules (having D m ¼ 0, i.e., C 1m ¼ C 2m , see also Fig. 2), the M II phase is always favored, that is, the calculated energy per lipid F b /n 0 A in the M II phase is equal to the reference value and is the smallest comparing to the energy of the L a and the H II phase. We note that for isotropic molecules there can be no energy lower- ing due to the average orientational ordering of the molecules since all orientations of the lipid molecules are energetically equivalent. ...
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... obtain a better agreement with experimental observations also in the intermediate range of jH m j ¼ D m , we include the effect of void filling energy by using a simple model, where the void-filling energy is considered constant for a given geometry (see also Ref. [24]). Figure 12 shows the minimal free energy F/n 0 A ¼ F b /n 0 A þ F i /n 0 A in dependence on the intrinsic mean curvature H m for the L a , H II , and M II phases. Here F i is the interstitial energy, n 0 is the area density of the lipid molecule, and A is the area of the whole monolayer (see Eqs. (39) and (54)). ...
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... F i is the interstitial energy, n 0 is the area density of the lipid molecule, and A is the area of the whole monolayer (see Eqs. (39) and (54)). Since the energy contribution of voids is smaller in the system of close packed inverted Figure 11 The equilibrium bending energy per lipid molecule F b /n 0 A in dependence on the intrinsic mean curvature H m for the L a , M II , and H II phases: (A) a system composed of anisotropic molecules (D m ¼ jH m j) and (B) a system composed of isotropic molecules (D m ¼ 0). For the bending contribution, see Eq. (58). ...
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... Fig. 12A and B the curves corresponding to the H II and M II phases in Fig. 11 are shifted up for different constants w, respectively, and the overall picture is now more realistic. It can be seen in Fig. 12A and B that for small D m ¼ jH m j the L a phase is energetically the most favorable, since it requires no void-filling energy. For ...
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... Fig. 12A and B the curves corresponding to the H II and M II phases in Fig. 11 are shifted up for different constants w, respectively, and the overall picture is now more realistic. It can be seen in Fig. 12A and B that for small D m ¼ jH m j the L a phase is energetically the most favorable, since it requires no void-filling energy. For anisotropic molecules (Fig. 12A) at a certain threshold D m ¼ jH m j, the H ...
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... Fig. 12A and B the curves corresponding to the H II and M II phases in Fig. 11 are shifted up for different constants w, respectively, and the overall picture is now more realistic. It can be seen in Fig. 12A and B that for small D m ¼ jH m j the L a phase is energetically the most favorable, since it requires no void-filling energy. For anisotropic molecules (Fig. 12A) at a certain threshold D m ¼ jH m j, the H II phase becomes energetically the most favorable due to the average orientational ordering of the lipid molecules. In the ...
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... B the curves corresponding to the H II and M II phases in Fig. 11 are shifted up for different constants w, respectively, and the overall picture is now more realistic. It can be seen in Fig. 12A and B that for small D m ¼ jH m j the L a phase is energetically the most favorable, since it requires no void-filling energy. For anisotropic molecules (Fig. 12A) at a certain threshold D m ¼ jH m j, the H II phase becomes energetically the most favorable due to the average orientational ordering of the lipid molecules. In the isotropic case (Fig. 12B), all curves monotonously increase; however, the curve corresponding to the L a phase increases faster and therefore it would eventually cross ...
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... 12A and B that for small D m ¼ jH m j the L a phase is energetically the most favorable, since it requires no void-filling energy. For anisotropic molecules (Fig. 12A) at a certain threshold D m ¼ jH m j, the H II phase becomes energetically the most favorable due to the average orientational ordering of the lipid molecules. In the isotropic case (Fig. 12B), all curves monotonously increase; however, the curve corresponding to the L a phase increases faster and therefore it would eventually cross with the curve corresponding to the H II phase. However, the value of H m where the intersection would take place would be very high (out of range given in Fig. 12, where the maximal value 0.4 nm ...
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... lipid molecules. In the isotropic case (Fig. 12B), all curves monotonously increase; however, the curve corresponding to the L a phase increases faster and therefore it would eventually cross with the curve corresponding to the H II phase. However, the value of H m where the intersection would take place would be very high (out of range given in Fig. 12, where the maximal value 0.4 nm À1 already corresponds to a cylinder with a radius of only 1.25 ...
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... short, the effects shown in Fig. 12A indicate that in the simple model where the interstitial energy is taken to be constant within a phase [24,29], an increase of D m ¼ jH m j, which is caused by the increase of temperature can induce the transformation from L a to H II lipid phase. Taking into account the interstitial energy for small jH m j (lower temperature) renders, ...
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... eliminated the M II phase due to high packing frustration (Fig. 12), in the following, we compare only the L a and the H II phases by using an improved model for the void filling energy, where stretching of the lipid tails in the actual hexagonal geometry is taken into account (Fig. 6 and Eq. (52)). Figure 13 shows the free energy per lipid molecule F/n 0 A in dependence on the intrinsic mean curvature ...
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... Figure 13 shows the free energy per lipid molecule F/n 0 A in dependence on the intrinsic mean curvature H m for the L a and the H II phase. ...
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... can compare the total free energy per molecule for anisotropic and isotropic phospholipid molecules in dependence on the mean intrinsic curvature H m . It can be seen in Fig. 13 that there are three curves corresponding to the inverted hexagonal phase with different stiffness con- stants t and one curve corresponding to the lamellar phase. For stiff hydro- carbon chains (high values of t), the lamellar phase has lower energy than the inverted hexagonal phase, while for decreasing t, the inverted hexago- nal ...
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... comparing Fig. 13A and B, it is important to point out that the anisotropy of phospholipid molecules evokes a steeper increase of the absolute value of the energy difference between the lamellar and the inverted hexagonal phases with temperature and therefore promotes and stabilizes the H II phase profoundly. For a more detailed study of the H II phase ...
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... a more detailed study of the H II phase we have constructed graphs its structural parameters. Figure 14 shows the dependence of the cylinder radius r and of the distance between the centers of the lipid cylinders a, respectively, (Fig. 6), on the intrinsic curvature jH m j for three values of t of anisotropic lipid molecules. The H II phase is composed of lipid cylinders with small radius r and small separation a for lipids of large mean intrinsic curvatures. ...
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... stretching of hydrocarbon chains. Therefore, the maximum radii of the cylinders are limited by the energy of interface region between the cylinders. If the hydrocarbon chains are stiff (large value of t), the creation of voids is energetically unfavorable. In this case, the small radii of cylinders are preferred as they provide small void spaces (Fig. 14A). On the other hand, if the stretching of hydrocarbon chains does not require much energy (small t), larger radii of hydrocarbon chains are ...
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... is instructive to compare the given plots with experimental data [28,34] (Fig. 14, dashed lines). First, it teaches us that realistic value of the stretching moduli t most probably lie between 0 and 20kT nm À2 (for large enough t, e.g., t ¼ 95kT nm À2 no realistic dimensions of the H II lattice can be predicted). Second, the range of realistic intrinsic mean curvatures ÀH m lies probably in the range of 0.1À0.2 nm À1 . Note that ...
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... diameter of the lipid cylinder r produces larger voids that are energetically unfavorable. Figure 15 shows the effect of the direct interaction constant ~ k [21] on the calculated free energy per lipid molecule. The energy ~ k=kT was estimated by the van der Waals interactions between the tails of orientationally ordered and orientationally disordered nearest neighbors of a given mole- cule [21]. ...
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... can be seen in Fig. 15 that for low values of ~ k=kT the behavior of the anisotropic lipid molecules in our theoretical model are energetically close to the behavior of isotropic ...
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... the nucleation model of the L a -H II transition given in [28,34], the surface of the monolayer forming a closure is described by the radius vector r ¼ (x, y, z(x)) (Figs. 7 and 16), wherefrom the mean and the Gaussian curvatures ...
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... phase and f L a is the energy per lipid molecule in the lamellar phase at given values of model constants. From top to bottom, the stretching modulus of the phospholipids is increased: t ¼ (0.95 and 9.5) kT nm À2 . From left to right the lipid intrinsic mean curvature jH m j ¼ 0 is increased: jH m j ¼ (0, 0.15, 0.3) nm À1 . It can be seen in Fig. 17 that the inverted hexagonal phase (H II ) configu- ration is energetically more favorable than the pure lamellar L a phase at sufficiently high values of the mean intrinsic curvature jH m j. In the model increase of the temperature is simulated by increasing of jH m j. For higher values of the mean intrinsic curvature jH m j, the ...
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... is evident from Fig. 17 that the radius of the cylinder r decreases with increasing stretching modulus of the phospholipid chains t and increasing jH m j which is in agreement with the results presented in Fig. 14. Creation of a cylinder in the lamellar phase becomes less disturbing for adjacent lipid layers when the radius of the cylinder r is decreased ...
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... is evident from Fig. 17 that the radius of the cylinder r decreases with increasing stretching modulus of the phospholipid chains t and increasing jH m j which is in agreement with the results presented in Fig. 14. Creation of a cylinder in the lamellar phase becomes less disturbing for adjacent lipid layers when the radius of the cylinder r is decreased ...
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... transition from the L a to H II phase in the nucleation model occurs at the energy difference Df ¼ 0, that is, when the energy of H II phase is equal to energy of L a phase for jH m j ¼ D m , (Fig. 18). By comparison of three different configurations of H II phase nucleation corresponding to different phospholipid chain stiffness, one can see that for low t the L a -H II transition takes place for smaller jH m j and the predicted radius of initial cylinder does not have a realistic value (r ¼ 3.49 nm), that is, it is much larger ...
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... [28,34]. However, for larger values of t the calculated r corresponds to experimental values much better. At jH m j ¼ 0.155 nm À1 the nucleation cylinder radius is 2.47 nm, which agrees well with data obtained from X-ray experiments [28,49]. As the decrease of the free energy with increasing jH m j is more pronounced in the pure hexagonal phase (Fig. 13) than in the nucleation configuration (Fig. 18), the values of t around 9.5kT nm À2 would lead to the stabilization of the H II phase at higher temperatures. For large t (e.g., t ¼ 95kT nm À2 ), the predicted nucleation transition is again less realistic due to the too small value of r ¼ 1.49 ...
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... calculated r corresponds to experimental values much better. At jH m j ¼ 0.155 nm À1 the nucleation cylinder radius is 2.47 nm, which agrees well with data obtained from X-ray experiments [28,49]. As the decrease of the free energy with increasing jH m j is more pronounced in the pure hexagonal phase (Fig. 13) than in the nucleation configuration (Fig. 18), the values of t around 9.5kT nm À2 would lead to the stabilization of the H II phase at higher temperatures. For large t (e.g., t ¼ 95kT nm À2 ), the predicted nucleation transition is again less realistic due to the too small value of r ¼ 1.49 ...
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... our theoretical analysis we did not take into account the dependence of the chain stretching modulus t on the temperature [55], which is based on the elasticity of lipid chains. We expect that neglecting the temperature dependency of t predicts that the slope of the energy dependence of jH m j is less pronounced (Fig. 13). Another simplification introduced in our theo- retical model is the assumption of spherical cross sections of lipid tubes in the H II phase. The nonspherical cross section of lipid tubes would probably lower the stretching energy of phospholipid chains, but would also contrib- ute to higher bending of the monolayer. To include the ...
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... Figure also shows a phospholipid bilayer (b), a cylindrical micelle (c) and an inverted cylinder (d). Adapted with permission from ref. [5]. 2009 Elsevier. ...
... where K 1 and K 2 are constants [21,90]. Equation (5) can be rewritten as (Equation (6)): ...
Biological membranes are composed of isotropic and anisotropic curved nanodomains. Anisotropic membrane components, such as Bin/Amphiphysin/Rvs (BAR) superfamily protein domains, could trigger/facilitate the growth of membrane tubular protrusions, while isotropic curved nanodomains may induce undulated (necklace-like) membrane protrusions. We review the role of isotropic and anisotropic membrane nanodomains in stability of tubular and undulated membrane structures generated or stabilized by cyto- or membrane-skeleton. We also describe the theory of spontaneous self-assembly of isotropic curved membrane nanodomains and derive the critical concentration above which the spontaneous necklace-like membrane protrusion growth is favorable. We show that the actin cytoskeleton growth inside the vesicle or cell can change its equilibrium shape, induce higher degree of segregation of membrane nanodomains or even alter the average orientation angle of anisotropic nanodomains such as BAR domains. These effects may indicate whether the actin cytoskeleton role is only to stabilize membrane protrusions or to generate them by stretching the vesicle membrane. Furthermore, we demonstrate that by taking into account the in-plane orientational ordering of anisotropic membrane nanodomains, direct interactions between them and the extrinsic (deviatoric) curvature elasticity, it is possible to explain the experimentally observed stability of oblate (discocyte) shapes of red blood cells in a broad interval of cell reduced volume. Finally, we present results of numerical calculations and Monte-Carlo simulations which indicate that the active forces of membrane skeleton and cytoskeleton applied to plasma membrane may considerably influence cell shape and membrane budding.
... These experimental results strongly support the theoretical results presented in this work, showing that without the actin force only anisotropic membrane components may facilitate the formation of tubular membrane protrusions. The comparison of theoretical and experimental results (Perutková et al. 2009(Perutková et al. , 2011Rappolt et al. 2008) indicates that the concept of the anisotropic shape of lipid molecules and their in-plane ordering may also better explain the phase transition between the fluid lamellar phase L α and the inverse hexagonal phase H II . In addition, the deviatoric bending of anisotropic lipid molecules may explain the stability of the inverse hexagonal phase H II at higher temperatures (Perutková et al. 2009). ...
... The comparison of theoretical and experimental results (Perutková et al. 2009(Perutková et al. , 2011Rappolt et al. 2008) indicates that the concept of the anisotropic shape of lipid molecules and their in-plane ordering may also better explain the phase transition between the fluid lamellar phase L α and the inverse hexagonal phase H II . In addition, the deviatoric bending of anisotropic lipid molecules may explain the stability of the inverse hexagonal phase H II at higher temperatures (Perutková et al. 2009). A similar idea was also expressed earlier in Templer (1998), but was not applied to any model calculations. ...
Eukaryote cells have a flexible shape, which dynamically changes according to the function performed by the cell. One mechanism for deforming the cell membrane into the desired shape is through the expression of curved membrane proteins. Furthermore, these curved membrane proteins are often associated with the recruitment of the cytoskeleton, which then applies active forces that deform the membrane. This coupling between curvature and activity was previously explored theoretically in the linear limit of small deformations, and low dimensionality. Here we explore the unrestricted shapes of vesicles that contain active curved membrane proteins, in three-dimensions, using Monte-Carlo numerical simulations. The activity of the proteins is in the form of protrusive forces that push the membrane outwards, as may arise from the cytoskeleton of the cell due to actin or microtubule polymerization occurring near the membrane. For proteins that have an isotropic convex shape, the additional protrusive force enhances their tendency to aggregate and form membrane protrusions (buds). In addition, we find another transition from deformed spheres with necklace type aggregates, to flat pancake-shaped vesicles, where the curved proteins line the outer rim. This second transition is driven by the active forces, coupled to the spontaneous curvature, and the resulting configurations may shed light on the organization of the lamellipodia of adhered and motile cells.
... These experimental results strongly support the theoretical results presented in this work, showing that without the actin force only anisotropic membrane components may facilitate the formation of tubular membrane protrusions. The comparison of theoretical and experimental results (Perutková et al. 2009(Perutková et al. , 2011Rappolt et al. 2008) indicates that the concept of the anisotropic shape of lipid molecules and their in-plane ordering may also better explain the phase transition between the fluid lamellar phase L α and the inverse hexagonal phase H II . In addition, the deviatoric bending of anisotropic lipid molecules may explain the stability of the inverse hexagonal phase H II at higher temperatures (Perutková et al. 2009). ...
... The comparison of theoretical and experimental results (Perutková et al. 2009(Perutková et al. , 2011Rappolt et al. 2008) indicates that the concept of the anisotropic shape of lipid molecules and their in-plane ordering may also better explain the phase transition between the fluid lamellar phase L α and the inverse hexagonal phase H II . In addition, the deviatoric bending of anisotropic lipid molecules may explain the stability of the inverse hexagonal phase H II at higher temperatures (Perutková et al. 2009). A similar idea was also expressed earlier in Templer (1998), but was not applied to any model calculations. ...
Biological membranes are composed of different components and there is no a priori reason to assume that all components are isotropic. It was previously shown that the anisotropic properties of membrane components may explain the stability of membrane tubular protrusions even without the application of external force. Our theoretical study focuses on the role of anisotropic membrane components in the stability of membrane tubular structures generated or stabilized by actin filaments. We show that the growth of the actin cytoskeleton inside the vesicle can induce the partial lateral segregation of different membrane components. The entropy of mixing of membrane components hinders the total lateral segregation of the anisotropic and isotropic membrane components. Self-assembled aggregates formed by anisotropic membrane components facilitate the growth of long membrane tubular protrusions. Protrusive force generated by actin filaments favors strong segregation of membrane components by diminishing the opposing effect of mixing entropy.
... Isotropically shaped molecules (with rotational symmetry) such as a cone or a cylinder tend to form spherical micelles or flat bilayers, respectively. Anisotropic shapes, as given in wedge-shaped molecules, promote self-assembling into tubular-shaped structures, while more complicated double-wedge-shaped molecules lead to the formation of saddle-like surfaces in bicontinuous cubic phases [96][97][98]. Quantitatively, molecular shape is expressed by the critical packing parameter (CPP) [99]: ...
Along having various health benefits, flavonoids are increasingly being recognized as potent antioxidants and anticancer compounds. However, despite significant efforts over the last few decades to develop novel delivery systems providing higher drug bioavailability, many biofunctional aspects are still unsolved. In this chapter, we review the current knowledge on flavonoid-lipid interactions and elucidate in particular their influence on lipidic self-assembled mesophases. The interactions of flavonoids with phospholipid-based planar membranes and monoglycerides-based curved membranes are presented in detail; the main structural changes in these self-assemblies are summarized, and the correlation between membranes' structure and function is discussed. Based on those considerations, especially the importance of membrane curvature and possible biological implications are highlighted.
... The H II structure has only been observed in the liquidcrystalline state. In the gel phase the acyl chains are not flexible enough to adapt to the high curvature of the H II structure [17][18][19][20]. ...
Glycolipids are amphiphilic molecules which bear an oligo- or polysaccharide as hydrophilic head group and hydrocarbon chains in varying numbers and lengths as hydrophobic part. They play an important role in life science as well as in material science. Their biological and physiological functions are quite diverse, ranging from mediators of cell-cell recognition processes, constituents of membrane domains or as membrane-forming units. Glycolipids form an exceptional class of liquid-crystal mesophases due to the fact that their self-organisation obeys more complex rules as compared to classical monophilic liquid-crystals. Like other amphiphiles, the supra-molecular structures formed by glycolipids are driven by their chemical structure; however, the details of this process are still hardly understood. Based on the synthesis of specific glycolipids with a clearly defined chemical structure, e.g., type and length of the sugar head group, acyl chain linkage, substitution pattern, hydrocarbon chain lengths and saturation, combined with a profound physico-chemical characterisation of the formed mesophases, the principles of the organisation in different aggregate structures of the glycolipids can be obtained. The importance of the observed and formed phases and their properties are discussed with respect to their biological and physiological relevance. The presented data describe briefly the strategies used for the synthesis of the used glycolipids. The main focus, however, lies on the thermotropic as well as lyotropic characterisation of the self-organised structures and formed phases based on physico-chemical and biophysical methods linked to their potential biological implications and relevance.
Small hydrophobic gold nanoparticles with diameter lower than the membrane thickness can form clusters or uniformly distribute within the hydrophobic core of the bilayer. The coexistence of two stable phases (clustered and dispersed) indicates the energy barrier between nanoparticles. We calculated the distance dependence of the membrane-mediated interaction between two adjacent nanoparticles. In our model we consider two deformation modes: the monolayer bending and the hydroxycarbon chain stretching. Existence of an energy barrier between the clustered and the separated state of nanoparticles was predicted. Variation analysis of the membrane mechanical parameters revealed that the energy barrier between two membrane embedded nanoparticles is mainly the consequence of the bending deformation and not change of the thickness of the bilayer in the vicinity of nanoparticles. It is shown, that the forces between the nanoparticles embedded in the biological membrane could be either attractive or repulsive, depending on the mutual distance between them.
Nanoscale topography on various titanium surfaces has already been shown to improve vascular response in vitro. To propose a novel strategy for translation into clinically used vascular implants, it is imperative that the surface should also be properly conditioned to provide a better environment for adhesion and proliferation of cells. Electrochemical anodization process is one of the well-established strategies to produce controlled nanotopographic features on the surface of titanium. By combining electrochemical anodization process and gaseous plasma surface modification, it would be possible to fine-tune surface properties to enable improved biological response for specific application. The key surface properties that may influence biological responses, such as surface topography, surface chemistry, and surface wettability were studied in detail and their influences on in vitro biological responses were evaluated. Performance of platelets, human coronary artery endothelial cells (HCAEC), and stem cells on those surfaces was studied. It was shown that altering nanotube diameter (electrochemical anodization) and changing surface chemistry and wettability (gaseous plasma modification) significantly influenced platelet adhesion and activation as well as proliferation of HCAEC. The results provide evidence that by combining specific nanotopographic features and surface chemical modification by gaseous oxygen plasma, the optimized surface features necessary for improved performance of vascular implants in coronary arteries could be achieved.
Natural and synthetic antimicrobial peptides (AMPs) show interesting features, and they are considered possible alternatives to common antibiotics which might induce resistance in bacteria. We present a comparative study of the interaction of two homologous AMPs with lipids mimicking the cytoplasmic membrane of prokaryotic and eukaryotic cells. The peptides were derived from the membranolytic protein NK-lysin. Phosphatidylcholine (PC) was used as a representative of human erythrocytes and phosphatidylethanolamine (PE) was chosen to build the model cytoplasmic membrane of Escherichia coli. Although the sequences of the investigated peptides vary only in one position, they show a difference in activity against E. coli. The results of small angle X-ray scattering and differential scanning calorimetry revealed that these two analogs behaved differently upon interaction with PE liposomes. One of the peptides significantly decreased the temperature of the hexagonal phase transition, inducing a negative membrane curvature, whereas the second one shifted the phase transition temperature to higher values. No influence on the lipid phase behavior or the bilayer structure was detected after mixing the peptides with PC vesicles. This observation completed the results of the hemolytic assay, where the toxic effect of the peptides on the red blood cells was not found.
In recent years, lipid based nanostructures have increasingly been used as model membranes to study various complex biological processes. For better understanding of such phenomena, it is essential to gain as much information as possible for model lipid structures under physiological conditions. In this paper, we focus on one of such lipids--monoelaidin (ME)--for its polymorphic nanostructures under varying conditions of temperature and water content. In the recent contribution (Soft Matter, 2010, 6, 3191), we have reported the phase diagram of ME above 30 °C and compared with the phase behavior of other lipids including monoolein (MO), monovaccenin (MV), and monolinolein (ML). Remarkable phase behavior of ME, stabilizing three bicontinuous cubic phases, motivates its study at low temperatures. Current studies concentrate on the low-temperature (<30 °C) behavior of ME and subsequent reconstruction of its phase diagram over the entire temperature-water composition space (temperature, 0-76 °C; and water content, 0-70%). The polymorphs found for the monoelaidin-water system include three bicontinuous cubic phases, i.e., Ia3d, Pn3m, and Im3m, and lamellar phases which exhibit two crystalline (L(c1) and L(c0)), two gel (L(β) and L(β*)), and a fluid lamellar (L(α)) states. The fluid isotropic phase (L(2)) was observed only for lower hydrations (<20%), whereas hexagonal phase (H(2)) was not found under studied conditions. Nanostructural parameters of these phases as a function of temperature and water content are presented together with some molecular level calculations. This study might be crucial for perception of the lyotropic phase behavior as well as for designing nanostructural assemblies for potential applications.
