Mechanical properties of nano-sized vesicles made up of natural membranes are crucial to the development of stable, biocompatible nanocontainers with enhanced functional, recognition and sensing capabilities. Here we measure and compare the mechanical properties of plasma and inner membrane nanovesicles ∼80 nm in diameter obtained from disrupted yeast Saccharomyces cerevisiae cells. We provide evidence of a highly deformable behaviour for these vesicles, able to support repeated wall-to-wall compressions without irreversible deformations, accompanied by a noticeably high Young's modulus (∼300 MPa) compared to that obtained for reconstituted artificial liposomes of similar size and approaching that of some virus particles. Surprisingly enough, the results are approximately similar for plasma and inner membrane nanovesicles, in spite of their different lipid compositions, especially on what concerns the ergosterol content. These results point towards an important structural role of membrane proteins in the mechanical response of natural membrane vesicles and open the perspective to their potential use as robust nanocontainers for bioapplications.

The finding of cardiolipin analogs in the extreme halophilic Archaea arises from an investigation into the characteristics of delipidated bacteriorhodopsin (BR), the photoactivated proton pump in the purple membrane (PM) of Halobacterium salinarum (1).By analyzing lipids of delipidated BR fractions by electrospray ionization-mass spectrometry (ESI-MS), it was found that the composition of the residual lipids in delipidated BR is different from that of the PM in that the delipidated fractions have much higher proportions of two bicharged peaks at 760 m/z and 966 m/z , corresponding to two novel membrane lipids. This suggested that these novel lipids are more resistant to detergents than the other lipid components of PM, or, alternatively, that the novel lipids are more strongly bound to BR and may be involved in stabilizing the BR trimer structure.The two novel PM lipids were isolated, purified by thinlayer chromatography (TLC), and analyzed by conventional analytical and spectroscopic methods to determine their chemical structure. Combining ESI-MS data and proton and phosphorus nuclear magnetic resonance (NMR) data of the purified novel lipids, together with the identification of their acid degradation products, allowed the elucidation of the chemical structures of the novel PM phospholipids (2). Their structures are, respectively, of a phosphosulfoglycolipid, 3-HSO 3 -Gal p ␤ 1-6Man p ␣ 1-2Glc p ␣ -1-1-[ sn -2,3-di-O -phytanylglycerol]-6-[phospho-sn -2,3-di-O -phytanylglycerol] (called glycocardiolipin, or GlyC), and a glyceroldiether analog of bisphosphatidylglycerol,

The lipidome of the marine hyperthermophilic archaeon Pyrococcus furiosus was studied by means of combined thin-layer chromatography and MALDI-TOF/MS analyses of the total lipid extract. 80–90% of the major polar lipids were represented by archaeol lipids (diethers) and the remaining part by caldarchaeol lipids (tetraethers). The direct analysis of lipids on chromatography plate showed the presence of the diphytanylglycerol analogues of phosphatidylinositol and phosphatidylglycerol, the N-acetylglucosamine-diphytanylglycerol phosphate plus some caldarchaeol lipids different from those previously described. In addition, evidence for the presence of the dimeric ether lipid cardiolipin is reported, suggesting that cardiolipins are ubiquitous in archaea.

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The present report illustrates the response to osmotic stress of an extreme halophilic archaeon, Halorubrum sp., isolated from the saltern ponds of Margherita di Savoia in southern Italy. The hypotonic stress induces relevant changes in the membrane lipid composition: archaeal cardiolipin content markedly increases, whereas phosphatidylglycerol (PG) decreases. Membranes isolated from this archaeon after cell disruption by osmotic shock are highly enriched in archaeal cardiolipin and reveal the presence of a novel phospholipid. Electrospray ionization mass spectrometry and NMR analyses revealed that this novel lipid has the structure of a sulfo-diglyco-diether-phosphatidic acid, i.e., a phospholipid dimer or a novel cardiolipin analogue. As NMR analyses showed that the sugars in the novel phospholipid dimer are the same and in the same order of a sulfated diglycosyl diphytanylglycerol diether (S-DGD-5) present as a major lipid component in the archaeon membranes, the novel phospholipid dimer was named S-DGD-5-PA. We conclude that osmotic shock induces a specific increase in the membrane content of the two cardiolipins and suggest that PG and S-DGD-5 are intermediates for the de novo synthesis of archaeal cardiolipin and S-DGD-5-PA, respectively. -Lopalco, P., S. Lobasso, F. Cardiolipin, a dimeric phospholipid discovered in heart mitochondria, plays an important role in the function and stability of many enzymatic complexes of the respiratory chain (1). A number of substituted cardiolipins or cardiolipin analogues have been described in bacteria (2-4); the function of these cardiolipin analogues in bacteria is still unclear. Both authentic cardiolipin and cardiolipin analogues are composed of two diacylglycerol moieties and therefore possess four hydrophobic chains.Cardiolipins have also been found in the Archaea world (5, 6). The first evidence of the presence of archaeal cardiolipin was found in Halobacterium salinarum , in which a bisphosphatidylglycerol (BPG) and another phospholipid dimer composed of the glycolipid sulfated triglycosyl diphytanylglycerol diether-1 (S-TGD-1) esterified to phosphatidic acid (PA) have been described [S-TGD-1-PA, also called glycocardiolipin (GlyC)] (5).GlyC, a major lipid component of the purple membrane (PM) of H. salinarum , plays an important role in the function and stability of bacteriorhodopsin (BR), the photoactivated proton pump (7), whereas BPG is only a minor lipid of PM (5, 8). Interestingly, it has been shown that the amount of GlyC in the PM of H. salinarum increases when the cells are exposed to hypotonic shock and that the formation of GlyC occurs at the expense of S-TGD-1 (9).In the present report, we show that a halo-archaeal isolate collected from the salterns of Margherita di Savoia in southern Italy, which is closely related to Halorubrum trapanicum , actively synthesizes high amounts of the archaeal cardiolipin BPG under osmotic shock. Membranes isolated after cell disruption by osmotic shock are highly enriched in this archaeal cardiolipin and reve...