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From vesicles to protocells: the roles of amphiphilic molecules.

Sakuma Y, Imai M - Life (Basel) (2015)

Bottom Line: It is very challenging to construct protocells from molecular assemblies.Here, we show that simple binary phospholipid vesicles have the potential to reproduce the relevant functions of adhesion, pore formation and self-reproduction of vesicles, by coupling the lipid geometries (spontaneous curvatures) and the phase separation.This achievement will elucidate the pathway from molecular assembly to cellular life.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Tohoku University, Aoba, Sendai 980-8578, Japan. sakuma@bio.phys.tohoku.ac.jp.

ABSTRACT
It is very challenging to construct protocells from molecular assemblies. An important step in this challenge is the achievement of vesicle dynamics that are relevant to cellular functions, such as membrane trafficking and self-reproduction, using amphiphilic molecules. Soft matter physics will play an important role in the development of vesicles that have these functions. Here, we show that simple binary phospholipid vesicles have the potential to reproduce the relevant functions of adhesion, pore formation and self-reproduction of vesicles, by coupling the lipid geometries (spontaneous curvatures) and the phase separation. This achievement will elucidate the pathway from molecular assembly to cellular life.

No MeSH data available.


Related in: MedlinePlus

Snapshots of the formation (time evolution at 38.9 °C) (a) and closing (temperature dependence) (b) of a pore in GUV with DPPC:DHPC = 99:1. When a pore opens, a small vesicle is ejected through the pore, as shown by the arrows in (a). Scale bar is 5 μm (taken from [49]).
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life-05-00651-f018: Snapshots of the formation (time evolution at 38.9 °C) (a) and closing (temperature dependence) (b) of a pore in GUV with DPPC:DHPC = 99:1. When a pore opens, a small vesicle is ejected through the pore, as shown by the arrows in (a). Scale bar is 5 μm (taken from [49]).

Mentions: We demonstrate stable pore formation using binary GUVs composed of cone- and cylinder-shaped lipids [49]. The binary GUV shows a phase separation between a solid phase that is rich in cylinder-shaped lipids and a liquid phase that is rich in cone-shaped lipids. The segregated cone-shaped lipids might form a cap at the edge of the bilayer due to the geometrical preference, which may stabilize the pore, as shown in Figure 17. The cone-shaped lipid-induced pore formation was realized by using binary GUV composed of 1,2-dihexanoyl-sn-glycero-3-phosphocoline (DHPC: cone-shaped lipid, Tm = −46 °C) and DPPC (cylinder-shaped lipid, Tm = 41 °C). In water, DHPC molecules form micelles with a size of ca. 2.0 nm [65], indicating that a DHPC molecule has a cone shape with a spontaneous curvature of ca. 0.5 nm−1. In the one-phase region above the Tm of DPPC, the binary GUVs showed a spherical shape with radii of 10–30 μm, where both lipids are mixed homogeneously at the molecular scale. For the temperature decreases to below the Tm of DPPC, the spherical GUVs showed a burst at temperatures below Tm of DPPC, as shown in Figure 18a. The cross-section area of a DPPC molecule below the Tm is approximately 78% of that above Tm [45]. This decrease in the molecular area increases the tension of the vesicle membrane, resulting in membrane fracture. After the burst, a spherical GUV had a single pore, and the inner solution was released from the vesicle through the pore, as shown by the arrow in Figure 18a. The pore was stable below the Tm of DPPC, because the segregated cone-shaped lipids cap the edge of the bilayer at the rim of the pore, which decreases the line tension at the rim. In contrast, DPPC in the solid state solidifies the main body of the GUV. A unique feature of the pore formation in the binary GUV containing the cone-shaped lipids is that the pore opening and closing could be controlled by the temperature. For increases in the temperature of the GUV with a pore to the one-phase region, the pore started to shrink and closed just below the Tm of DPPC, as shown in Figure 18b. The GUV recovered its spherical shape as a result of the chain melting. Similar pore formations are observed for other pairs of cylinder-shaped lipids and cone-shaped lipid, i.e., 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC: Tm = 54 °C)/DHPC and 1,2-dipentadecanoyl-sn-glycero-3-phosphocholine (15:0 PC: Tm = 34 °C)/DHPC mixtures, where the pore-opening temperature increases with an increase in the main chain transition temperature [49]. Thus, the coupling between the lipid shape and the main chain transition is responsible for pore formation.


From vesicles to protocells: the roles of amphiphilic molecules.

Sakuma Y, Imai M - Life (Basel) (2015)

Snapshots of the formation (time evolution at 38.9 °C) (a) and closing (temperature dependence) (b) of a pore in GUV with DPPC:DHPC = 99:1. When a pore opens, a small vesicle is ejected through the pore, as shown by the arrows in (a). Scale bar is 5 μm (taken from [49]).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390873&req=5

life-05-00651-f018: Snapshots of the formation (time evolution at 38.9 °C) (a) and closing (temperature dependence) (b) of a pore in GUV with DPPC:DHPC = 99:1. When a pore opens, a small vesicle is ejected through the pore, as shown by the arrows in (a). Scale bar is 5 μm (taken from [49]).
Mentions: We demonstrate stable pore formation using binary GUVs composed of cone- and cylinder-shaped lipids [49]. The binary GUV shows a phase separation between a solid phase that is rich in cylinder-shaped lipids and a liquid phase that is rich in cone-shaped lipids. The segregated cone-shaped lipids might form a cap at the edge of the bilayer due to the geometrical preference, which may stabilize the pore, as shown in Figure 17. The cone-shaped lipid-induced pore formation was realized by using binary GUV composed of 1,2-dihexanoyl-sn-glycero-3-phosphocoline (DHPC: cone-shaped lipid, Tm = −46 °C) and DPPC (cylinder-shaped lipid, Tm = 41 °C). In water, DHPC molecules form micelles with a size of ca. 2.0 nm [65], indicating that a DHPC molecule has a cone shape with a spontaneous curvature of ca. 0.5 nm−1. In the one-phase region above the Tm of DPPC, the binary GUVs showed a spherical shape with radii of 10–30 μm, where both lipids are mixed homogeneously at the molecular scale. For the temperature decreases to below the Tm of DPPC, the spherical GUVs showed a burst at temperatures below Tm of DPPC, as shown in Figure 18a. The cross-section area of a DPPC molecule below the Tm is approximately 78% of that above Tm [45]. This decrease in the molecular area increases the tension of the vesicle membrane, resulting in membrane fracture. After the burst, a spherical GUV had a single pore, and the inner solution was released from the vesicle through the pore, as shown by the arrow in Figure 18a. The pore was stable below the Tm of DPPC, because the segregated cone-shaped lipids cap the edge of the bilayer at the rim of the pore, which decreases the line tension at the rim. In contrast, DPPC in the solid state solidifies the main body of the GUV. A unique feature of the pore formation in the binary GUV containing the cone-shaped lipids is that the pore opening and closing could be controlled by the temperature. For increases in the temperature of the GUV with a pore to the one-phase region, the pore started to shrink and closed just below the Tm of DPPC, as shown in Figure 18b. The GUV recovered its spherical shape as a result of the chain melting. Similar pore formations are observed for other pairs of cylinder-shaped lipids and cone-shaped lipid, i.e., 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC: Tm = 54 °C)/DHPC and 1,2-dipentadecanoyl-sn-glycero-3-phosphocholine (15:0 PC: Tm = 34 °C)/DHPC mixtures, where the pore-opening temperature increases with an increase in the main chain transition temperature [49]. Thus, the coupling between the lipid shape and the main chain transition is responsible for pore formation.

Bottom Line: It is very challenging to construct protocells from molecular assemblies.Here, we show that simple binary phospholipid vesicles have the potential to reproduce the relevant functions of adhesion, pore formation and self-reproduction of vesicles, by coupling the lipid geometries (spontaneous curvatures) and the phase separation.This achievement will elucidate the pathway from molecular assembly to cellular life.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Tohoku University, Aoba, Sendai 980-8578, Japan. sakuma@bio.phys.tohoku.ac.jp.

ABSTRACT
It is very challenging to construct protocells from molecular assemblies. An important step in this challenge is the achievement of vesicle dynamics that are relevant to cellular functions, such as membrane trafficking and self-reproduction, using amphiphilic molecules. Soft matter physics will play an important role in the development of vesicles that have these functions. Here, we show that simple binary phospholipid vesicles have the potential to reproduce the relevant functions of adhesion, pore formation and self-reproduction of vesicles, by coupling the lipid geometries (spontaneous curvatures) and the phase separation. This achievement will elucidate the pathway from molecular assembly to cellular life.

No MeSH data available.


Related in: MedlinePlus