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Effects of lipid composition and solution conditions on the mechanical properties of membrane vesicles.

Kato N, Ishijima A, Inaba T, Nomura F, Takeda S, Takiguchi K - Membranes (Basel) (2015)

Bottom Line: Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine.Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect.These results show that the mechanical properties of liposomes depend on their lipid composition and environment.

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. k614899x@m2.aichi-c.ed.jp.

ABSTRACT
The mechanical properties of cell-sized giant unilamellar liposomes were studied by manipulating polystyrene beads encapsulated within the liposomes using double-beam laser tweezers. Mechanical forces were applied to the liposomes from within by moving the beads away from each other, which caused the liposomes to elongate. Subsequently, a tubular membrane projection was generated in the tip at either end of the liposome, or the bead moved out from the laser trap. The force required for liposome transformation reached maximum strength just before formation of the projection or the moving out of the bead. By employing this manipulation system, we investigated the effects of membrane lipid compositions and environment solutions on the mechanical properties. With increasing content of acidic phospholipids, such as phosphatidylglycerol or phosphatidic acid, a larger strength of force was required for the liposome transformation. Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine. Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect. These results show that the mechanical properties of liposomes depend on their lipid composition and environment.

No MeSH data available.


Related in: MedlinePlus

(a) Plot of the force exerted on a bead (vertical, pN) against the increase in separation between two beads encapsulated in a liposome (horizontal, μm). Two examples are shown, a case when the liposome forms a tubular membrane projection (blue) and a case when the bead moves out from the laser trap during liposome deformation (green). Each plot (thin line) was approximated by sixth-order equation (thick line); (b) and (c) Sequences of phase contrast images (each upper) and their models (each lower) showing the deformation processes of liposomes. Liposomes were made from phosphatidylcholine (PC) and phosphatidylglycerol (PG) obtained from native sources (4:1, mol/mol). Milli-Q water was used to swell the lipid films to prepare liposomes. Observations and measurements were carried out at 25 °C. In all experiments, to transform the liposomal membrane, separation between the two beads was increased at a constant speed of 125 nm/sec (refer to Section 3.3. for more information). (b) The process until just after the formation of a tubular projection from just after the initial elongation of a spherical liposome in a case when the liposome forms a projection. (c) The process until just before the moving out of the bead from the laser trap from just after the initial elongation of a spherical liposome. The images I–IV in (b) and V and VI in (c) are consistent with the symbols in (a). Bars indicate 10 μm. As one encapsulated polystyrene bead was moved away from the other one, a spherical giant unilamellar liposome (images I in (b) and V in (c)) formed two small bulge structures adjacent to both beads (images II and III in (b) and VI in (c)). Liposomes in this state are called lemon-shaped because of their morphology. In (b) and (c), the small bulge structures and the tubular membrane projection formed are indicated by arrowheads and an arrow, respectively.
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membranes-05-00022-f001: (a) Plot of the force exerted on a bead (vertical, pN) against the increase in separation between two beads encapsulated in a liposome (horizontal, μm). Two examples are shown, a case when the liposome forms a tubular membrane projection (blue) and a case when the bead moves out from the laser trap during liposome deformation (green). Each plot (thin line) was approximated by sixth-order equation (thick line); (b) and (c) Sequences of phase contrast images (each upper) and their models (each lower) showing the deformation processes of liposomes. Liposomes were made from phosphatidylcholine (PC) and phosphatidylglycerol (PG) obtained from native sources (4:1, mol/mol). Milli-Q water was used to swell the lipid films to prepare liposomes. Observations and measurements were carried out at 25 °C. In all experiments, to transform the liposomal membrane, separation between the two beads was increased at a constant speed of 125 nm/sec (refer to Section 3.3. for more information). (b) The process until just after the formation of a tubular projection from just after the initial elongation of a spherical liposome in a case when the liposome forms a projection. (c) The process until just before the moving out of the bead from the laser trap from just after the initial elongation of a spherical liposome. The images I–IV in (b) and V and VI in (c) are consistent with the symbols in (a). Bars indicate 10 μm. As one encapsulated polystyrene bead was moved away from the other one, a spherical giant unilamellar liposome (images I in (b) and V in (c)) formed two small bulge structures adjacent to both beads (images II and III in (b) and VI in (c)). Liposomes in this state are called lemon-shaped because of their morphology. In (b) and (c), the small bulge structures and the tubular membrane projection formed are indicated by arrowheads and an arrow, respectively.

Mentions: In this study, to expand understanding of membrane behavior and to mimic a situation close to pseudopod formation in living cells, we measured the strength of force required to change liposome shape using double-beam laser tweezers [33]. Laser tweezers are a technique to manipulate fine particles using a laser beam [34,35]. The trapping force has a spring-like property, and the technique enables the measurement in piconewtons (pN) of force and nanometers (nm) of position accuracy, using the captured particles as probes. Two polystyrene beads (each 1 μm in diameter) were encapsulated in giant liposomes and were manipulated away from each other using the double laser beams. Without any specific interaction between the lipid membrane and the beads, mechanical forces can be applied to the liposome membrane from the inside. The mechanical force exerted by the two beads pushes the liposome membrane from within and transforms liposomes from spheres into lemon-like shapes that have two small bulge structures adjacent to the two beads. In the elongation stage of the transformation to lemon-shaped liposomes, the force required for the transformation became larger as the end-to-end length increased (Figure 1a). Subsequently, a tubular membrane projection was generated in the tip at either end (Figure 1b), or in some cases, the beads moved out from the laser trap without developing a tubular projection, probably because the repulsive force exerted on the beads exceeded the trapping force of the laser (Figure 1c). This process is similar to the liposomal transformation caused by the elongation of encapsulated cytoskeletons. The force reached a maximum strength (about 10–20 pN) just before a tubular membrane was generated. However, once the membrane tube developed, a decreased and constant force (about 4 pN) was required for further tube elongation or shortening. In the latter case, the force required for the membrane transformation reached a maximum strength (about 10–20 pN) just before the bead moved out from the laser trap. After the moving out of the bead, the liposomes returned to their spherical shape. These results indicate that the simple application of a mechanical force is sufficient to deform spherical liposomes and to form protrusions in the membrane.


Effects of lipid composition and solution conditions on the mechanical properties of membrane vesicles.

Kato N, Ishijima A, Inaba T, Nomura F, Takeda S, Takiguchi K - Membranes (Basel) (2015)

(a) Plot of the force exerted on a bead (vertical, pN) against the increase in separation between two beads encapsulated in a liposome (horizontal, μm). Two examples are shown, a case when the liposome forms a tubular membrane projection (blue) and a case when the bead moves out from the laser trap during liposome deformation (green). Each plot (thin line) was approximated by sixth-order equation (thick line); (b) and (c) Sequences of phase contrast images (each upper) and their models (each lower) showing the deformation processes of liposomes. Liposomes were made from phosphatidylcholine (PC) and phosphatidylglycerol (PG) obtained from native sources (4:1, mol/mol). Milli-Q water was used to swell the lipid films to prepare liposomes. Observations and measurements were carried out at 25 °C. In all experiments, to transform the liposomal membrane, separation between the two beads was increased at a constant speed of 125 nm/sec (refer to Section 3.3. for more information). (b) The process until just after the formation of a tubular projection from just after the initial elongation of a spherical liposome in a case when the liposome forms a projection. (c) The process until just before the moving out of the bead from the laser trap from just after the initial elongation of a spherical liposome. The images I–IV in (b) and V and VI in (c) are consistent with the symbols in (a). Bars indicate 10 μm. As one encapsulated polystyrene bead was moved away from the other one, a spherical giant unilamellar liposome (images I in (b) and V in (c)) formed two small bulge structures adjacent to both beads (images II and III in (b) and VI in (c)). Liposomes in this state are called lemon-shaped because of their morphology. In (b) and (c), the small bulge structures and the tubular membrane projection formed are indicated by arrowheads and an arrow, respectively.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4384090&req=5

membranes-05-00022-f001: (a) Plot of the force exerted on a bead (vertical, pN) against the increase in separation between two beads encapsulated in a liposome (horizontal, μm). Two examples are shown, a case when the liposome forms a tubular membrane projection (blue) and a case when the bead moves out from the laser trap during liposome deformation (green). Each plot (thin line) was approximated by sixth-order equation (thick line); (b) and (c) Sequences of phase contrast images (each upper) and their models (each lower) showing the deformation processes of liposomes. Liposomes were made from phosphatidylcholine (PC) and phosphatidylglycerol (PG) obtained from native sources (4:1, mol/mol). Milli-Q water was used to swell the lipid films to prepare liposomes. Observations and measurements were carried out at 25 °C. In all experiments, to transform the liposomal membrane, separation between the two beads was increased at a constant speed of 125 nm/sec (refer to Section 3.3. for more information). (b) The process until just after the formation of a tubular projection from just after the initial elongation of a spherical liposome in a case when the liposome forms a projection. (c) The process until just before the moving out of the bead from the laser trap from just after the initial elongation of a spherical liposome. The images I–IV in (b) and V and VI in (c) are consistent with the symbols in (a). Bars indicate 10 μm. As one encapsulated polystyrene bead was moved away from the other one, a spherical giant unilamellar liposome (images I in (b) and V in (c)) formed two small bulge structures adjacent to both beads (images II and III in (b) and VI in (c)). Liposomes in this state are called lemon-shaped because of their morphology. In (b) and (c), the small bulge structures and the tubular membrane projection formed are indicated by arrowheads and an arrow, respectively.
Mentions: In this study, to expand understanding of membrane behavior and to mimic a situation close to pseudopod formation in living cells, we measured the strength of force required to change liposome shape using double-beam laser tweezers [33]. Laser tweezers are a technique to manipulate fine particles using a laser beam [34,35]. The trapping force has a spring-like property, and the technique enables the measurement in piconewtons (pN) of force and nanometers (nm) of position accuracy, using the captured particles as probes. Two polystyrene beads (each 1 μm in diameter) were encapsulated in giant liposomes and were manipulated away from each other using the double laser beams. Without any specific interaction between the lipid membrane and the beads, mechanical forces can be applied to the liposome membrane from the inside. The mechanical force exerted by the two beads pushes the liposome membrane from within and transforms liposomes from spheres into lemon-like shapes that have two small bulge structures adjacent to the two beads. In the elongation stage of the transformation to lemon-shaped liposomes, the force required for the transformation became larger as the end-to-end length increased (Figure 1a). Subsequently, a tubular membrane projection was generated in the tip at either end (Figure 1b), or in some cases, the beads moved out from the laser trap without developing a tubular projection, probably because the repulsive force exerted on the beads exceeded the trapping force of the laser (Figure 1c). This process is similar to the liposomal transformation caused by the elongation of encapsulated cytoskeletons. The force reached a maximum strength (about 10–20 pN) just before a tubular membrane was generated. However, once the membrane tube developed, a decreased and constant force (about 4 pN) was required for further tube elongation or shortening. In the latter case, the force required for the membrane transformation reached a maximum strength (about 10–20 pN) just before the bead moved out from the laser trap. After the moving out of the bead, the liposomes returned to their spherical shape. These results indicate that the simple application of a mechanical force is sufficient to deform spherical liposomes and to form protrusions in the membrane.

Bottom Line: Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine.Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect.These results show that the mechanical properties of liposomes depend on their lipid composition and environment.

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. k614899x@m2.aichi-c.ed.jp.

ABSTRACT
The mechanical properties of cell-sized giant unilamellar liposomes were studied by manipulating polystyrene beads encapsulated within the liposomes using double-beam laser tweezers. Mechanical forces were applied to the liposomes from within by moving the beads away from each other, which caused the liposomes to elongate. Subsequently, a tubular membrane projection was generated in the tip at either end of the liposome, or the bead moved out from the laser trap. The force required for liposome transformation reached maximum strength just before formation of the projection or the moving out of the bead. By employing this manipulation system, we investigated the effects of membrane lipid compositions and environment solutions on the mechanical properties. With increasing content of acidic phospholipids, such as phosphatidylglycerol or phosphatidic acid, a larger strength of force was required for the liposome transformation. Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine. Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect. These results show that the mechanical properties of liposomes depend on their lipid composition and environment.

No MeSH data available.


Related in: MedlinePlus