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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

Binary phase diagrams containing coexisting solid and liquid phases. (a) At high temperatures, Components A and B mix completely in one uniform liquid phase. An arbitrary mixture of A and B is shown at Point P. (b) When the temperature is quenched, the phase boundary is crossed, and the system separates along the tie-line into a solid phase rich in Component A and a liquid phase rich in Component B (taken from [46]). (c) The fluorescence micrograph for phase separated binary GUV composed of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) (rich in solid phase) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (rich in liquid phase). s, solid.
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life-05-00651-f008: Binary phase diagrams containing coexisting solid and liquid phases. (a) At high temperatures, Components A and B mix completely in one uniform liquid phase. An arbitrary mixture of A and B is shown at Point P. (b) When the temperature is quenched, the phase boundary is crossed, and the system separates along the tie-line into a solid phase rich in Component A and a liquid phase rich in Component B (taken from [46]). (c) The fluorescence micrograph for phase separated binary GUV composed of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) (rich in solid phase) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (rich in liquid phase). s, solid.

Mentions: Binary vesicles composed of two types of lipids having different geometries are good model systems to demonstrate the shape deformation caused by geometrical frustration. Phospholipids are composed of a phosphate-based hydrophilic moiety and an acyl chain-based hydrophobic moiety. The acyl chains of the lipids exhibit a main chain transition, i.e., order-disorder transition of acyl chains, when the temperature changes. The melting temperature depends on the length and/or the chemical structure (double bonds and side chains) of the acyl chain. It should be noted that the cross-section area of the lipid increases upon chain melting. For 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), having a chain melting temperature (Tm) of 41 °C, the cross-section area increases from 47.9 Å2 (20 °C) to 64 Å2 (50 °C) [45]. A schematic phase diagram of lipid membranes composed of high Tm lipids and low Tm lipids is shown in Figure 8a [46]. At high temperatures, a mixture of the two components in one uniform liquid phase is observed. Between high Tm and low Tm, the system separates into coexisting solid (s) and liquid (l) phases (Figure 8b). The phase separation is visualized using fluorescence dyes that prefer to localize in the liquid phase. A fluorescence micrograph of a phase separated, binary GUV composed of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE, Tm = 63 °C) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC, Tm = −20 °C) is shown in Figure 8c. In the image, the dark domain (solid phase) is strongly enriched in high Tm lipids (DPPE), whereas the bright domain (liquid phase) is rich in low Tm lipids (DOPC). The domains grow through a diffusion and coalescence mechanism. The liquid domains have a circular shape due to the line tension, whereas the solid domains prefer to form a diffusion-limited aggregation shape (dendritic pattern) [47], as shown in Figure 8c. Two solid phases can be immiscible at low temperatures, as shown in Figure 8a. Using the phase separation into solid and liquid phases, we can laterally segregate the lipids having different shapes.


From vesicles to protocells: the roles of amphiphilic molecules.

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

Binary phase diagrams containing coexisting solid and liquid phases. (a) At high temperatures, Components A and B mix completely in one uniform liquid phase. An arbitrary mixture of A and B is shown at Point P. (b) When the temperature is quenched, the phase boundary is crossed, and the system separates along the tie-line into a solid phase rich in Component A and a liquid phase rich in Component B (taken from [46]). (c) The fluorescence micrograph for phase separated binary GUV composed of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) (rich in solid phase) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (rich in liquid phase). s, solid.
© Copyright Policy
Related In: Results  -  Collection

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

life-05-00651-f008: Binary phase diagrams containing coexisting solid and liquid phases. (a) At high temperatures, Components A and B mix completely in one uniform liquid phase. An arbitrary mixture of A and B is shown at Point P. (b) When the temperature is quenched, the phase boundary is crossed, and the system separates along the tie-line into a solid phase rich in Component A and a liquid phase rich in Component B (taken from [46]). (c) The fluorescence micrograph for phase separated binary GUV composed of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) (rich in solid phase) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (rich in liquid phase). s, solid.
Mentions: Binary vesicles composed of two types of lipids having different geometries are good model systems to demonstrate the shape deformation caused by geometrical frustration. Phospholipids are composed of a phosphate-based hydrophilic moiety and an acyl chain-based hydrophobic moiety. The acyl chains of the lipids exhibit a main chain transition, i.e., order-disorder transition of acyl chains, when the temperature changes. The melting temperature depends on the length and/or the chemical structure (double bonds and side chains) of the acyl chain. It should be noted that the cross-section area of the lipid increases upon chain melting. For 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), having a chain melting temperature (Tm) of 41 °C, the cross-section area increases from 47.9 Å2 (20 °C) to 64 Å2 (50 °C) [45]. A schematic phase diagram of lipid membranes composed of high Tm lipids and low Tm lipids is shown in Figure 8a [46]. At high temperatures, a mixture of the two components in one uniform liquid phase is observed. Between high Tm and low Tm, the system separates into coexisting solid (s) and liquid (l) phases (Figure 8b). The phase separation is visualized using fluorescence dyes that prefer to localize in the liquid phase. A fluorescence micrograph of a phase separated, binary GUV composed of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE, Tm = 63 °C) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC, Tm = −20 °C) is shown in Figure 8c. In the image, the dark domain (solid phase) is strongly enriched in high Tm lipids (DPPE), whereas the bright domain (liquid phase) is rich in low Tm lipids (DOPC). The domains grow through a diffusion and coalescence mechanism. The liquid domains have a circular shape due to the line tension, whereas the solid domains prefer to form a diffusion-limited aggregation shape (dendritic pattern) [47], as shown in Figure 8c. Two solid phases can be immiscible at low temperatures, as shown in Figure 8a. Using the phase separation into solid and liquid phases, we can laterally segregate the lipids having different shapes.

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