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Abstract
The biological activity of farnesol (FN) and geranylgeraniol (GG) and their isoprenyl groups is related to membrane-associated processes. We have studied the interactions of FN and GG with 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) membranes using DSC and X-ray diffraction. Storage of samples at low temperature for a long time favors a multidomain system formed by a lamellar crystalline (Lc) phase and isoprenoids (ISPs) aggregates. We demonstrate that ISPs alter the thermotropic behavior of DEPE, thereby promoting a HII growth in a lamellar Lc phase with a reduced degree of hydration. The HII phase occurs with the same repeat distance (dHII=5.4 nm) as the Lc phase and upon heating it expands considerably (δd/δT≈0.22 nm/°C). The dimensional stabilization of this HII phase coincides with the transition temperature of the Lc to Lα phase. Thereafter, the system DEPE/ISP will progress by increasing the nonlamellar-forming propensity and reaching a single HII phase at high temperature. The cooling scan followed a similar structural path, except that the system went into a stable gel phase Lβ with a repeat distance, dLβ=6.5 nm, in co-existence with a HII phase. The formation of ISP microdomains in model PE membranes substantiates the importance of the isoprenyl group in the binding of isoprenylated proteins to membranes and in lipid–lipid interactions through modulation of the membrane structure.
| Abbreviations | ||
| FN | = | farnesol |
| GG | = | geranylgeraniol |
| ISP | = | isoprenoid |
| PL | = | phospholipid |
| PC | = | phosphocholine |
| PE | = | phosphoethanolamine |
| DEPE | = | 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine |
| Lβ | = | gel lamellar phase |
| Lc | = | lamellar-crystalline phase |
| Lα | = | liquid-crystalline lamellar phase |
| HII | = | inverted hexagonal phase |
| Tm | = | gel-to-liquid lamellar phase transition temperature |
| TH | = | lamellar-to-hexagonal phase transition temperatures |
| Abbreviations | ||
| FN | = | farnesol |
| GG | = | geranylgeraniol |
| ISP | = | isoprenoid |
| PL | = | phospholipid |
| PC | = | phosphocholine |
| PE | = | phosphoethanolamine |
| DEPE | = | 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine |
| Lβ | = | gel lamellar phase |
| Lc | = | lamellar-crystalline phase |
| Lα | = | liquid-crystalline lamellar phase |
| HII | = | inverted hexagonal phase |
| Tm | = | gel-to-liquid lamellar phase transition temperature |
| TH | = | lamellar-to-hexagonal phase transition temperatures |
Notes
1A similar phase was analysed by DSC and 31P NMR and it was called “subgel” phase (Lewis R, Mannock DA, McElhaney RN 1989). Effect of fatty acyl chain length and structure on the lamellar gel to liquid-crystalline and lamellar to reversed hexagonal phase transitions of aqueous phosphatidylethanolamine dispersions. Biochemistry 28: 541–548).