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Intermolecular interaction of phosphatidylinositol with the lipid raft molecules sphingomyelin and cholesterol

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ABSTRACT

Diacylphosphatidylinositol (PI) is the starting reactant in the process of phosphatidylinositide-related signal transduction mediated through the lipid raft domain. We investigated intermolecular interactions of PI with major raft components, sphingomyelin (SM) and cholesterol (Chol), using surface pressure–molecular area (π–A) isotherm measurements. The classical mean molecular area versus composition plot showed that the measured mean molecular areas are smaller in PI/Chol mixed monolayers and larger in PI/SM mixed monolayers than those calculated on the basis of the ideal additivity. These results indicate that PI interacts attractively with Chol and repulsively with SM. In addition, we energetically evaluated the interaction of PI with SM/Chol mixtures and found that the mixing energy of PI/SM/Chol ternary monolayers decreased as the molar ratio of Chol to SM increased. In order to quantitatively analyze the distribution of PI we calculated the chemical potentials of mixing of PI into the SM/Chol mixed monolayer and into the dioleoylphosphatidylcholine (DOPC) monolayer, which was used as a model for the fluid matrix, on the basis of partial molecular area analysis. Analysis using the chemical potential of mixing of PI suggested that partition of PI molecules between these two monolayers can be changed by a factor of about 1.7 in response to change in Chol molar fraction in the SM/Chol mixed monolayer from 0.3 to 0.6 when the concentration of PI in the DOPC monolayer is kept constant at 7 mol%.

No MeSH data available.


Intermolecular interaction in the PI/SM monolayer system. (a) π–A isotherms of pure PI, pure SM and PI/SM mixed monolayers on the water subphase at 25±0.1°C. The molar fractions of PI, XPI, are indicated in the figure; 0 (SM), 0.3, 0.5, 0.7, 0.9 and 1.0 (PI). The isotherms with XPI= 0.5 and 0.9 were nearly superposed upon those of XPI= 0.7 and 1.0, respectively. (b) Mean molecular area versus composition analysis at 30 mN/m. The dotted line represents area additivity for ideal mixing of two components (Eq. (1)). (c) Areal compressional modulus () versus composition analysis. The  values at 30 mN/m were calculated from equation (4). The solid line represents ideal additivity of compressibility (see Materials and methods and Eq. (5)).
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f1-4_1: Intermolecular interaction in the PI/SM monolayer system. (a) π–A isotherms of pure PI, pure SM and PI/SM mixed monolayers on the water subphase at 25±0.1°C. The molar fractions of PI, XPI, are indicated in the figure; 0 (SM), 0.3, 0.5, 0.7, 0.9 and 1.0 (PI). The isotherms with XPI= 0.5 and 0.9 were nearly superposed upon those of XPI= 0.7 and 1.0, respectively. (b) Mean molecular area versus composition analysis at 30 mN/m. The dotted line represents area additivity for ideal mixing of two components (Eq. (1)). (c) Areal compressional modulus () versus composition analysis. The values at 30 mN/m were calculated from equation (4). The solid line represents ideal additivity of compressibility (see Materials and methods and Eq. (5)).

Mentions: We examined intermolecular interaction of diacylphosphatidylionsitol (PI) with two major raft components, sphingomyelin (SM) and cholesterol (Chol), and with a model lipid for the fluid matrix, dioleoylphospatidylcholine (DOPC). First, the surface pressure versus molecular area (π–A) isotherms for pure PI, pure SM and PI/SM monolayers at 25.0±0.1°C are shown in Figure 1a. The isotherm for the pure SM monolayer showed a low slope region (π=14–26 mN/m) corresponding to the phase transition between liquid expanded (LE) and liquid condensed (LC) phases as described previously23,24,33 though the transition is obscure due to heterogeneity of chain species in SM molecules. With increasing molar fraction of PI the isotherm shifted toward the higher molecular area, changing its shape.


Intermolecular interaction of phosphatidylinositol with the lipid raft molecules sphingomyelin and cholesterol
Intermolecular interaction in the PI/SM monolayer system. (a) π–A isotherms of pure PI, pure SM and PI/SM mixed monolayers on the water subphase at 25±0.1°C. The molar fractions of PI, XPI, are indicated in the figure; 0 (SM), 0.3, 0.5, 0.7, 0.9 and 1.0 (PI). The isotherms with XPI= 0.5 and 0.9 were nearly superposed upon those of XPI= 0.7 and 1.0, respectively. (b) Mean molecular area versus composition analysis at 30 mN/m. The dotted line represents area additivity for ideal mixing of two components (Eq. (1)). (c) Areal compressional modulus () versus composition analysis. The  values at 30 mN/m were calculated from equation (4). The solid line represents ideal additivity of compressibility (see Materials and methods and Eq. (5)).
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Related In: Results  -  Collection

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f1-4_1: Intermolecular interaction in the PI/SM monolayer system. (a) π–A isotherms of pure PI, pure SM and PI/SM mixed monolayers on the water subphase at 25±0.1°C. The molar fractions of PI, XPI, are indicated in the figure; 0 (SM), 0.3, 0.5, 0.7, 0.9 and 1.0 (PI). The isotherms with XPI= 0.5 and 0.9 were nearly superposed upon those of XPI= 0.7 and 1.0, respectively. (b) Mean molecular area versus composition analysis at 30 mN/m. The dotted line represents area additivity for ideal mixing of two components (Eq. (1)). (c) Areal compressional modulus () versus composition analysis. The values at 30 mN/m were calculated from equation (4). The solid line represents ideal additivity of compressibility (see Materials and methods and Eq. (5)).
Mentions: We examined intermolecular interaction of diacylphosphatidylionsitol (PI) with two major raft components, sphingomyelin (SM) and cholesterol (Chol), and with a model lipid for the fluid matrix, dioleoylphospatidylcholine (DOPC). First, the surface pressure versus molecular area (π–A) isotherms for pure PI, pure SM and PI/SM monolayers at 25.0±0.1°C are shown in Figure 1a. The isotherm for the pure SM monolayer showed a low slope region (π=14–26 mN/m) corresponding to the phase transition between liquid expanded (LE) and liquid condensed (LC) phases as described previously23,24,33 though the transition is obscure due to heterogeneity of chain species in SM molecules. With increasing molar fraction of PI the isotherm shifted toward the higher molecular area, changing its shape.

View Article: PubMed Central - PubMed

ABSTRACT

Diacylphosphatidylinositol (PI) is the starting reactant in the process of phosphatidylinositide-related signal transduction mediated through the lipid raft domain. We investigated intermolecular interactions of PI with major raft components, sphingomyelin (SM) and cholesterol (Chol), using surface pressure–molecular area (π–A) isotherm measurements. The classical mean molecular area versus composition plot showed that the measured mean molecular areas are smaller in PI/Chol mixed monolayers and larger in PI/SM mixed monolayers than those calculated on the basis of the ideal additivity. These results indicate that PI interacts attractively with Chol and repulsively with SM. In addition, we energetically evaluated the interaction of PI with SM/Chol mixtures and found that the mixing energy of PI/SM/Chol ternary monolayers decreased as the molar ratio of Chol to SM increased. In order to quantitatively analyze the distribution of PI we calculated the chemical potentials of mixing of PI into the SM/Chol mixed monolayer and into the dioleoylphosphatidylcholine (DOPC) monolayer, which was used as a model for the fluid matrix, on the basis of partial molecular area analysis. Analysis using the chemical potential of mixing of PI suggested that partition of PI molecules between these two monolayers can be changed by a factor of about 1.7 in response to change in Chol molar fraction in the SM/Chol mixed monolayer from 0.3 to 0.6 when the concentration of PI in the DOPC monolayer is kept constant at 7 mol%.

No MeSH data available.