Possible molecular evolution of biomembranes: from single-chain to double-chain lipids.

We have studied a possible evolution process permitting a 'primitive' membrane to evolve towards a membrane structure with an outer wall, similar to that of bacteria. We have investigated whether a polysaccharide bearing hydrophobic phytyl or cholesteryl chains coats giant vesicles made of single- or double-chain lipids. Phytyl-pullulan 5b was found to bind to the surface of vesicles made of either single- or double-chain lipids.

"Primitive" membrane from polyprenyl phosphates and polyprenyl alcohols.

Polyprenyl phosphates, as well as polyprenyl alcohols bearing different isopentenyl C(5) units, have been synthesized. The pH range of spontaneous vesicle formation of polyprenyl phosphates with or without polyprenyl alcohols was defined by fluorescence microscopy. A variety of the acyclic or monocyclic polyprenyl phosphates studied formed stable vesicles in water over a wide range of pHs, and the addition of polyprenyl alcohols allowed the vesicle formation of polyprenyl phosphates at higher pHs.

Membrane properties of branched polyprenyl phosphates, postulated as primitive membrane constituents.

We have postulated earlier that the highly branched isoprenoid alkanes, which are distributed widely in many sediments, may have been derived from the corresponding branched polyprenyl phosphates, potentially present in biomembranes in primitive organisms. These polyprenyl-branched polyprenyl phosphates might be derived by a simple alkylation from non-substituted polyprenyl phosphates, which we postulate to be the precursors of all membrane terpenoids. We have now synthesized a series of 6-(poly)prenyl-substituted polyprenyl phosphates and studied the formation of vesicles from these phosphates, as a function of the substituted-chain length, the position of the double bond, and pH.

A novel type of membranes based on cholesteryl phosphate.

Mixtures of the rigid amphiphile disodium cholesteryl phosphate (DCP) with the non-phosphorylated diacyl amphiphile dimyristoylglycerol (DMG) give self-organized systems in a wide range of pH, as demonstrated by differential microcalorimetry. These systems can be closed bilayer vesicles, as shown by optical microscopy (Nomarski and confocal). Neither DMG nor DCP, taken alone, give vesicles in these conditions but 10% DMG is enough to lead to the formation of vesicles from pH 5.

Monolayer studies of single-chain polyprenyl phosphates.

The monolayer properties of some single-chain polyprenyl phosphates (phytanyl, phytyl, and geranylgeranyl phosphates), which we regard as hypothetical primitive membrane lipids, were investigated at the air-water interface by surface pressure-area (pi-A) isotherm measurements. The molecular area/ pressure at various pH conditions dependence revealed the acid dissociation constants (pKa values) of the phosphate. The pKa values thus obtained at the air-water interface (pKa1 = 7.

Regioselective photolabeling of glycoprotein A in membranes.

We have developed a chemical method for directly identifying the amino acid residues of the transmembrane domain of a protein that are located right in the center of the membrane. Glycophorin A (GPA), the major sialoglycoprotein of human erythrocytes, was the first membrane protein whose primary sequence was elucidated, but its three-dimensional structure is still not known. GPA has been reconstituted into liposomes formed from dimyristoylphosphatidylcholine, dimyristoylphosphatidylserine, cholesterol, and a bola-amphiphilic phospholipidic photoactivatable probe (radioactive probe 1) by a detergent-mediated method.

Mid-Membrane Photolabeling of the Transmembrane Domain of Glycophorin A in Phospholipid Vesicles.

The tandem use of the photosensitive bola-amphiphile 1 (X= H) and cholesterol enabled the determination of the center of the transmembrane domain of glycophorin A (131 amino acid residues) in a membrane by selective functionalization of the protein within a phospholipid bilayer.

Synthesis of Deuterium-Labeled Plant Sterols and Analysis of Their Side-Chain Mobility by Solid State Deuterium NMR.

The plant sterols sitosterol and stigmasterol exert very different effects on plant model membranes, the first one being a "reinforcer" like cholesterol, the second one not. 25-(2)H-Stigmasterol has been synthesized by coupling of the 22-aldehyde derived from stigmasterol by ozonolysis, with the proper sulfone labeled in position 25. The configuration of the ethyl side chain at C-24 was controlled by separation of the diastereomers introduced via a chiral sulfoxide.