Phospholipid diversity: Correlation with membrane–membrane fusion events (original) (raw)
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Annexin-mediated membrane fusion of human neutrophil plasma membranes and phospholipid vesicles
Biochimica Et Biophysica Acta-biomembranes, 1991
Membrane fusion was studied using human neutrophil plasma membrane preparatiees and phosphotipkl vesicles approximately 0.15 #m in diameter and composed of phosphatidylserine and phosl~aticlylelhaaolamine in a ratio of I to 3. Lipasomes were labeled with No('J'-nitrobenzo-2.oxa.l,3-diazol-4-yl (NBD) and lissamine ~ine B derivatives of phospholip|ds. AppaRnt fusion was detected as an increase in fleerescence of the r-~ance enecgy transfer donor, NBD, after dilution of the probes into unlabeled membranes. 0.$ mM Ca 2+ alom was sefIkknt to cause substantial fusion of lipasomes with a plasma membrane preparation but not with other lipasomes. Both annexin I and des(1-9)annexin I caused a substantial increase in the rate of fusinn under these conditions while annexin V inhibited fusion. Fusion mediated by des(1-9)annexia I was observed at Ca :+ concentrations as low as ap~ximately $ #M, suggesting that the truncated form of this protein may be active at physiologically low Ca z+ concentrations. T~psin treated plasma membranes were incapable of fusion with Iil~ntes, sallgestinl that plasma membrane proteins may mediate fusien, Liimsomes did not fuse with whole cells at my Ca z+ ¢onctntration, indicating that the cytoplasmic side of the membrane is involved. These results st~lgest that anuexln ! aml unidentified plasma membrane proteins may play a role in Caz+-dependent desrannlatioa of human mtrol~ils.
The plasma membrane lipid composition affects fusion between cells and model membranes
Chemico-biological Interactions, 2006
Investigations were carried out on the effect of plasma membrane lipid modifications on the fusogenic capacity of control and ras-transformed fibroblasts. The plasma membrane lipid composition was modified by treatment of cells with exogenous phospholipases C and D, sphingomyelinase and cyclodextrin. The used enzymes hydrolyzed definite membrane lipids thus inducing specific modifications of the lipid composition while cyclodextrin treatment reduced significantly the level of cholesterol. The cells with modified membranes were used for assessment of their fusogenic capacity with model membranes with a constant lipid composition. Treatment with phospholipases C and D stimulated the fusogenic potential of both cell lines whereas the specific reduction of either sphingomyelin or cholesterol induced the opposite effect. The results showed that all modifications of the plasma membrane lipid composition affected the fusogenic capacity irrespective of the initial differences in the membrane lipid composition of the two cell lines. These results support the notion that the lipid composition plays a significant role in the processes of membrane-membrane fusion. This role could be either direct or through modulation of the activity of specific proteins which regulate membrane fusion.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1981
We have investigated the contribution of various phospholipids to membrane fusion induced by divalent cations. Fusion was followed by means of a new fluorescence assay monitoring the mixing of internal aqueous contents of large (0.1 #m diameter) unilamellar liposomes. The rate and extent of fusion induced by Ca 2÷ in mixed phosphatidylserine/phosphatidylcholine vesicles were lower compared to those in pure phosphatidylserine vesicles. The presence of 50% phosphatidylcholine completely inhibited fusion, although the vesicles aggregated upon Ca 2÷ addition. When phosphatidylserine was mixed with phosphatidylethanolamine, however, rapid fusion could be induced by Ca 2÷ even in mixtures that contained only 25% phosphatidylserine. Phosphatidylethanolamine also facilitated fusion by Mg 2÷ which could not fuse pure phosphatidylserine vesicles. In phosphatidylserine/phosphatidylethanolamine/phosphatidylcholine mixtures, in which the phosphatidylcholine content was kept at 25%, phosphatidylethanolamine could not substitute for phosphatidylserine, and the fusogenic capacity of Mg 2÷ was abolished by the presence of merely 10% phosphatidylcholine. The initial rate of relelase of vesicle contents was slower than the rate of fusion in all the mixtures used. The presence of phosphate effected a considerable decrease in the threshold concentration of Ca 2÷ and also enhanced
Evidence for the Extended Phospholipid Conformation in Membrane Fusion and Hemifusion
Biophysical Journal, 1999
Molecular-level mechanisms of fusion and hemifusion of large unilamellar dioleoyl phosphatidic acid/phosphocholine (DOPA/DOPC, 1:1 molar ratio) vesicles induced by millimolar Ca 2ϩ and Mg 2ϩ , respectively, were investigated using fluorescence spectroscopy. In keeping with reduction of membrane free volume V f , both divalent cations increased the emission polarization for 1,6-diphenyl-1,3,5-hexatriene (DPH). An important finding was a decrease in excimer/monomer emission intensity ratio (I e /I m ) for the intramolecular excimer-forming probe 1,2-bis[(pyren-1-)yl]decanoyl-sn-glycero-3-phosphocholine (bis-PDPC) in the course of fusion and hemifusion. Comparison with another intramolecular excimer-forming probe, namely, 1-[(pyren-1)-yl]decanoyl-2-[(pyren-1)-yl]tetradecanoyl-sn-glycero-3-phosphocholine (PDPTPC), allowed us to exclude changes in acyl chain alignment to be causing the decrement in I e /I m . As a decrease in V f should increase I e /I m for bis-PDPC and because contact site between adhering liposomes was required we conclude the most feasible explanation to be the adoption of the extended conformation (P.K.J. Kinnunen, 1992, Chem. Phys. Lipids 63:251-258) by bis-PDPC. In this conformation the two acyl chains are splaying so as to become embedded in the opposing leaflets of the two adhered bilayers, with the headgroup remaining between the adjacent surfaces. Our data provide evidence for a novel mechanism of fusion of the lipid bilayers.
Mechanisms of initiation of membrane fusion: role of lipids
Bioscience Reports, 2000
Main emphasis in studies on the mechanisms of fusion of cellular membranes has been in the roles of various proteins, with far less interest in the properties of lipids. Yet, on a molecular level fusion involves the merging of lipid bilayers. Studies so far have revealed lipids forming inverted non-lamellar phases to be important in controlling membrane fusion. However, the underlying molecular level mechanisms have remained controversial. While this review is focused on presenting one possible mechanism, involving so-called extended lipid conformation, we are also advocating the view, that in order to obtain a more complete understanding of this process it is necessary to merge the relevant physicochemical properties of lipids with the models describing the specific functions of proteins. To this end, taking into account the central importance of fusion in a wide range of cellular processes, we may anticipate its control to open novel possibilities also for therapeutic intervention. notation; SUVs, small unilamellar vesicles; X, mole fraction of the indicated lipid.
PLANT PHYSIOLOGY, 1990
Plasma membrane preparations of high purity (about 95%) are easily obtained by partitioning in aqueous polymer two-phase systems. These preparations, however, mainly contain sealed right-side-out (apoplastic side out) vesicles. Part of these vesicles have been turned inside-out by freezing and thawing, and sealed inside-out and right-side-out vesicles subsequently separated by repeating the phase partition step. Increasing the KCI concentration in the freeze/thaw medium as well as increasing the number of freeze/thaw cycles significantly increased the yield of insideout vesicles. At optimal conditions, 15 to 25% of total plasma membrane protein was recovered as inside-out vesicles, corresponding to 5 to 10 milligrams of protein from 500 grams of sugar beet (Beta vulgaris L.) leaves. Based on enzyme latency, trypsin inhibition of NADH-cytochrome c reductase, and H+ pumping capacity, a cross-contamination of about 20% between the two fractions of oppositely oriented vesicles was estimated. Thus, preparations containing about 80% inside-out and 80% rightside-out vesicles, respectively, were obtained. ATPase activity and H+ pumping were both completely inhibited by vanadate (K, ; 10 micromolar), indicating that the fractions were completely free from nonplasma membrane ATPases. Furthermore, the polypeptide patterns of the two fractions were close to identical, which shows that the vesicles differed in sidedness only. Thus, preparations of both inside-out and right-side-out plasma membrane vesicles are now available. This permits studies on transport, signal transduction mechanisms, enzyme topology, etc., using plasma membrane vesicles of either orientation.
Interplay between lipids and the proteinaceous membrane fusion machinery
Progress in Lipid Research, 2008
For membrane fusion to occur, opposed lipid bilayers initially establish a fusion pore, often followed by complete mixing of the fusing membranes. Contemporary views suggest that during fusion lipid bilayers are continuous passive platforms that are disrupted and remodeled by catalytic proteins. Some models propose that even the architecture and composition of the fusion pore might be dominated by proteins rather than lipids. Hence, lipids have no regulatory contribution to this process; they simply adapt their shape passively for filling space between otherwise autonomous protein machineries.