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1.
The conformations adopted by β-casein and the total apoprotein from serum high density lipoprotein when spread at the air-water interface are compared; the monolayer data are consistent with the apoprotein being α-helical and the β-casein being disordered with segments distributed in loops and trains. The penetration of these hydrophobic proteins into phosphatidylcholine monolayers in different physical states was investigated. More protein can penetrate into monolayers when they are in the liquid-expanded state; for penetration at constant total surface area the lateral compressibility of the lipid is an important factor. The charge and conformation of the polar group of the phospholipid does not have a major influence on the interaction. The mixed films of lipid and protein have a mosaic structure; probably the β-casein is in a compressed state whereas the apoprotein is extended as α-helices in the plane of the interface. The chain-length dependences of the interaction of the apoprotein with phosphatidylcholine monolayers and bilayers are different; when the apoprotein binds to bilayers of shorter-chain phosphatidylcholines it alters the shape of the lipid-water interface whereas with monolayers the interface remains planar throughout.  相似文献   

2.
The formation and stabilization of a complex between total erythrocyte apoprotein and monolayers of total erythrocyte lipid as measured by changes of surface pressure (Δπ) and rate of change of surface pressure (dπ/dt) was studied as a function of pH, ionic strength, and lipid surface pressure. Penetration of apoprotein into lipid monolayers was favored by conditions in which lipid and apoprotein were oppositely charged. Once the interaction was completed, the resultant surface complex was resistant to large changes in subphase pH and ionic strength as shown by the insensitivity of Δπ to these parameters. The dπ/dt, however, showed strong dependence on pH and ionic strength, but not on lipid surface pressure. A sharp decrease in dπ/dt around pH 3.5–4.5 is associated with the change in apoprotein charge from (+) to (?). Comparison of complex formation between apoprotein and bovine serum albumin, cytochrome c, and human hemoglobin suggests that erythrocyte apoprotein was specialized in its interaction with erythrocyte lipids. The data show that formation of an apoprotein-lipid complex at the air-water interface has both electrostatic and hydrophobic components. This contradicts results from other laboratories studying erythrocyte membrane recombination by bulk methods.  相似文献   

3.
A method for transferring a lipid monolayer from an air-water interface to an alkylated glass slide is described. Specific antibodies bind tightly to lipid haptens contained in these monolayers on the glass slides. We conclude that the polar head groups of the lipids face the aqueous phase. A monolayer containing a fluorescent lipid was used to show that the monolayer is homogeneous as observed with an epifluorescence microscope. A periodic pattern photobleaching technique was used to measure the lateral diffusion of this fluorescent lipid probe in monolayers composed of dipalmitoyl phosphatidylcholine and dimyristoyl phosphatidylcholine. Different regions of the pressure-area isotherms of the monolayers at the air-water interface can be correlated with the diffusion of the fluorescent probe molecules on the monolayer-coated glass slide. Monolayers derived from the so-called “solid-condensed” state of a monolayer at the air-water interface showed a very low probe diffusion coefficient in this monolayer when placed on a glass slide, D ≤ 10-10 cm2/s. Monolayers derived from the “liquid condensed/liquid expanded” (LC/LE) region of the monolayer isotherms at the air-water interface showed rapid diffusion (D > 10-8 cm2/s) when these same monolayers were observed on an alkylated glass slide. The monolayers attached to the glass slide appear to be homogeneous when derived from monolayers in the LC/LE region of monolayers at the air-water interface. There is no major variation of the diffusion coefficient of a fluorescent lipid probe when this diffusion is measured on a lipid monolayer on a glass slide, for monolayers derived from various regions of the LC/LE monolayers at the air-water interface. This is consistent with the view that the LC/LE region is most likely a single fluid phase. Monolayers supported on a planar glass substrate are of much potential interest for biophysical and biochemical studies of the interactions between model membranes and cellular membranes, and for physical chemical studies relating the properties of lipid monolayers to the properties of lipid bilayers.  相似文献   

4.
Toxicity mechanisms of Bacillus thuringiensis Cry insecticidal proteins involve membrane insertion and lytic pore formation in lipid bilayers of the target larval midgut cell membranes. The B. thuringiensis Cry4Ba mosquito-larvicidal protein has been shown to be capable of permeabilizing liposome vesicles and of forming ion channels in planar lipid bilayers. Here, the membrane interaction of the 65-kDa activated Cry4Ba protein with the lipid monolayers, comprising dipalmitoyl phosphatidylcholine, dioleoyl phosphatidylethanolamine, and cholesterol (Chol), was studied using Langmuir-Blodgett technique. The interactions of the Cry4Ba protein with the lipid monolayers were measured from the surface pressure versus area isotherms of the protein-lipid monolayers. The increase in the mean molecular area was demonstrated as an incorporation of the protein into lipid monolayers. The insertion of the Cry4Ba protein was monitored by measuring as an increase of the surface pressure at constant molecular area. For a given monolayer, the membrane insertion of the Cry4Ba reduced as the initial surface pressure increased. The Cry4Ba protein showed a strong preference of an insertion towards a Chol monolayer. In addition, the mixed monolayers of Chol showed an enhanced effect on the insertion kinetics of Cry4Ba into lipid films, suggesting its involvement in the modulation of the protein insertion. These findings provide the first evidence that the Cry4Ba protein is capable of inserting itself into lipid monolayers, depending on the packing density of the monolayers. Our results also indicate that only a limited part of the protein is likely to be involved in the insertion.  相似文献   

5.
The surface properties of colicin E1, a 522-amino acid protein, and its interaction with monolayers of Escherichia coli (E. coli) total lipid and 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DOPC) were studied using the Langmuir-Blodgett (LB) technique. Colicin E1 is amphiphilic, forming a protein monolayer at the air/buffer interface. The protein is thought to interact with the E. coli total lipid head groups through electrostatic interactions, followed by its insertion into the lipid monolayers. Supported lipid bilayers (SLBs) of E. coli total lipid and DOPC, deposited onto mica at the cell membrane equivalence pressure for E. coli and incubated with colicin E1, were imaged by contact mode atomic force microscopy (CM-AFM). Colicin E1 formed protein aggregates on DOPC SLBs, while E. coli total lipid SLB was deformed following its incubation with colicin E1. Corresponding lateral force images, along with electrostatic surface potentials for colicin E1 P190, imply a direct interaction of colicin E1 with lipid head groups facilitating their charge neutralization.  相似文献   

6.
The detailed molecular structure of the complex formed by the apoprotein from porcine high density lipoprotein and dimyristoly phosphatidylcholine (lecithin) has been investigated by a range of physical techniques. The complex, an oblate ellipsoid with major axis 11.0 nm and minor axis 5.5 nm (see the accompanying paper), is comprised of a section of lecithin bilayer with apoprotein at the surface. The main site of interaction between protein and lipid is in the lipid glycerophosphorylcholine group region; as with native high density lipoprotein the surface of the particle consists of a mosaic of lecithin polar groups and protein. The formation of this mosaic reduces the cooperativity of the lecithin chain motions and changes the curvature of the lipid-water interface, as compared to a bilayer. Otherwise, there are no major changes in lecithin motions indicating that no strong binding of lipid to protein occurs. The interaction involves the intercalation of amphipathic, 60% alpha-helical, apoprotein molecules among the lecithin molecules so that the protein residues at the lipid-water interface. The apoprotein has a high affinity for the lipid-water interface but specific lipid-protein interactions are not involved.  相似文献   

7.
1. The highest surface pressure of phosphatidylcholine monolayers allowing penetration of delipidated serum albumin decreased in the order dibehenoyl>distearoyl>dipalmitoyl=dimyristoyl. This pressure was not related to the area occupied or to the space available between the phospholipid molecules at the interface. 2. Penetration of albumin into yeast phosphatidylcholine monolayers was increased by adding a small percentage of long-chain anions (phosphatidic acid, dicetylphosphoric acid) to the film but only when the protein was below its isoelectric point (i.e. positively charged). 3. Stearylamine added to phosphatidylcholine monolayers had no effect on albumin penetration even when the protein was oppositely charged to that of the phospholipid/water interface. 4. The results are discussed in relation to the activation of certain phospholipases by anionic amphipathic substances.  相似文献   

8.
1. The interactions between cytochrome c (native and [(14)C]carboxymethylated) and monolayers of phosphatidylcholine, phosphatidic acid and cardiolipin at the air/water interface was investigated by measurements of surface radioactivity, pressure and potential. 2. On a subphase of 10mm-or m-sodium chloride, penetration of cytochrome c into egg phosphatidylcholine monolayers, as measured by an increase of surface pressure, and the number of molecules penetrating, as judged by surface radioactivity, were inversely proportional to the initial pressure of the monolayer and became zero at 20dynes/cm. The constant of proportionality was increased when the cytochrome c was carboxymethylated or decreased when the phospholipid was hydrogenated, but the cut-off point remained at 20dynes/cm. 3. Penetrated cytochrome c could be removed almost entirely by compression of the phosphatidylcholine monolayer above 20dynes/cm. 4. With phosphatidic acid and cardiolipin monolayers on 10mm-sodium chloride the binding of cytochrome c was much stronger and cytochrome c penetrated into films nearing the collapse pressure (>40dynes/cm.). The penetration was partly electrostatically facilitated, since it was decreased by carrying out the reaction on a subphase of m-sodium chloride, and the relationship between the surface pressure increment and the initial film pressure moved nearer to that observed with phosphatidylcholine. 5. Surface radioactivity determinations showed that [(14)C]carboxymethylated cytochrome c was still adsorbed on phosphatidic acid and cardiolipin monolayers after the cessation of penetration. This adsorption was primarily electrostatic in nature because it could be prevented and substantially reversed by adding m-sodium chloride to the subphase and there was no similar adsorption on phosphatidylcholine films. 6. The penetration into and adsorption on the three phospholipid monolayers was examined as a function of the pH of the subphase and compared with the state of ionization of both the phospholipid and the protein, and the area occupied by the latter at an air/water interface. 7. It is concluded that the binding of cytochrome c to phospholipids can only be partially understood by a consideration of the ionic interaction between the components and that subtle conformational changes in the protein must affect the magnitude and stability of the complex. 8. If cytochrome c is associated with a phospholipid in mitochondria then cardiolipin would fulfil the characteristics of the binding most adequately.  相似文献   

9.
We have utilized Fourier transform infrared spectroscopy to study the interaction of the antimicrobial peptide gramicidin S (GS) with lipid micelles and with lipid monolayer and bilayer membranes as a function of temperature and of the phase state of the lipid. Since the conformation of GS does not change under the experimental conditions employed in this study, we could utilize the dependence of the frequency of the amide I band of the central beta-sheet region of this peptide on the polarity and hydrogen-bonding potential of its environment to probe GS interaction with and location in these lipid model membrane systems. We find that the GS is completely or partially excluded from the gel states of all of the lipid bilayers examined in this study but strongly partitions into lipid micelles, monolayers, or bilayers in the liquid-crystalline state. Moreover, in general, the penetration of GS into zwitterionic and uncharged lipid bilayer coincides closely with the gel to liquid-crystalline phase transition of the lipid. However, GS begins to penetrate into the gel-state bilayers of anionic phospholipids prior to the actual chain-melting phase transition, while in cationic lipid bilayers, GS does not partition strongly into the liquid-crystalline bilayer until temperatures well above the chain-melting phase transition are reached. In the liquid-crystalline state, the polarity of the environment of GS indicates that this peptide is located primarily at the polar/apolar interfacial region of the bilayer near the glycerol backbone region of the lipid molecule. However, the depth of GS penetration into this interfacial region can vary somewhat depending on the structure and charge of the lipid molecule. In general, GS associates most strongly with and penetrates most deeply into more disordered bilayers with a negative surface charge, although the detailed chemical structure of the lipid molecule and physical organization of the lipid aggregate (micelle versus monolayer versus bilayer) also have minor effects on these processes.  相似文献   

10.
The surface properties of colicin E1, a 522-amino acid protein, and its interaction with monolayers of Escherichia coli (E. coli) total lipid and 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DOPC) were studied using the Langmuir-Blodgett (LB) technique. Colicin E1 is amphiphilic, forming a protein monolayer at the air/buffer interface. The protein is thought to interact with the E. coli total lipid head groups through electrostatic interactions, followed by its insertion into the lipid monolayers. Supported lipid bilayers (SLBs) of E. coli total lipid and DOPC, deposited onto mica at the cell membrane equivalence pressure for E. coli and incubated with colicin E1, were imaged by contact mode atomic force microscopy (CM-AFM). Colicin E1 formed protein aggregates on DOPC SLBs, while E. coli total lipid SLB was deformed following its incubation with colicin E1. Corresponding lateral force images, along with electrostatic surface potentials for colicin E1 P190, imply a direct interaction of colicin E1 with lipid head groups facilitating their charge neutralization.  相似文献   

11.
The interaction which occurs between an anti-lipid antibody (TEPC 15) and two phospholipids, phosphatidylcholine and phosphatidylethanolamine, when they are arranged in a lipid monolayer system has been studied. It is shown that the antibody is stabilised under the influence of a high lateral pressure when it is mixed with a lipid monolayer and that the behaviour of the antibody depends upon the lipid used. Measurements of the surface pressure and surface potential parameters of the lipid monolayers indicate that the antibody interacts differently with phosphatidylcholine compared with phosphatidylethanolamine. The antibody also exhibits a different interaction when it is pretreated with phosphorylcholine prior to being spread with a phosphatidylcholine monolayer. The interaction of the antibody with phosphatidylcholine-cholesterol monolayers has also been studied.  相似文献   

12.
Asymmetric lipid bilayers are formed by adjoining the hydrocarbon chains of two different lipid monolayers at the air-water interface through an aperture in a teflon partition separating two aqueous phases. It is shown that the addition of Ca2+ or polysine to the compartment limited by a monolayer of the neutral lipids glycerol dioleate or phosphatidylcholine results in no modification of the resistance and stability of the membrane, whereas a drastic decrease in both parameters is elicited by the presence of these ions on the opposite compartment containing a monolayer of the negatively charged cardiolipin or phosphatidylserine. The surface-charge dependence of this phenomenon indicates the persistence of the asymmetric lipid distribution in the bilayer after its formation from two different monolayers.  相似文献   

13.
As the main difference between bacterial and mammalian cell membranes is their net charge, the focal point of consideration in many model membrane experiments with antimicrobial peptides is lipid headgroup charge. We studied the interaction of the human multifunctional peptide LL-37 with single phospholipid monolayers, bilayers, and bilayers composed of binary mixtures of the four phospholipid species predominantly used in model membrane experiments (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylserine). We found that 1), the effects on single lipid monolayers are not comparable to those on the corresponding bilayers; 2), there are four different effects of LL-37 on bilayers of the four lipids; 3), the preference of LL-37 for the specific lipids is roughly inversely related to chain packing density; and 4), in the binary lipid mixtures, one lipid—and not necessarily the charged one—generally governs the mode of lipid/peptide interaction. Thus, our results show that lipid net charge is not the decisive factor determining the membrane-perturbing mechanism of LL-37, but only one of several parameters, among them packing density, the ability to form intermolecular H-bonds, and lipid molecular shape, which emphasizes how profoundly the choice of the model system can influence the outcome of a study of lipid/peptide interaction.  相似文献   

14.
A variety of proteins have been studied for their ability to interact and alter the thermotropic properties of phospholipid bilayer membranes as detected by differential scanning calorimeter. The proteins studied included: basic myelin protein (A1 protein), cytochrome c, major apoprotein of myelin proteolipid (N-2 apoprotein), gramicidin A, polylysine, ribonuclease and hemoglobin. The lipids used for the interactions were dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol. The interactions were grouped in three categories each having very different effects on the phospholipid phase transition from solid to liquid crystalline. The calorimetric studies were also correlated with data from vesicle permeability and monolayer expansion.Ribonuclease and polylysine which exemplify group 1 interactions, show strong dependence on electrostatic binding. Their effects on lipid bilayers include an increase in the enthalpy of transition (ΔH) accompanied by either an increase or no change in the temperature of transition (Tc). In addition, they show minimal effects on vesicle permeability and monolayer expansion. It was concluded that these interactions represent simple surface binding of the protein on the lipid bilayer without penetration into the hydrocarbon region.Cytochrome c and Al protein, which exemplify group 2 interactions, also show a strong dependence on the presence of net negative charges on the lipid bilayers for their binding. In contrast to the first group, however, they induce a drastic decrease in both Tc and ΔH of the lipid phase transition. Furthermore, they induce a large increase in the permeability of vesicles and a substantial expansion in area of closely packed monolayers at the air-water interface. It was concluded that group 2 interactions represent surface binding followed by partial penetration and/or deformation of the bilayer.Group 3 interactions, shown by proteolipid apoprotein and gramicidin A, were primarily non-polar in character, not requiring electrostatic charges and not inhibited by salt and pH changes. They had no appreciable effect on the Tc but did induce a linear decrease in the magnitude of the ΔH, proportional to the percentage of protein by weight. Membranes containing 50% proteolipid protein still exhibited a thermotropic transition with a ΔH one half that of the pure lipid, and only a small diminution of the size of the cooperative unit. It was concluded that in this case the protein was embedded within the bilayer, associating with a limited number of molecules via non-polar interactions, while the rest of the bilayer was largely unperturbed.  相似文献   

15.
A variety of proteins have been studied for their ability to interact and alter the thermotropic properties of phospholipid bilayer membranes as detected by differential scanning calorimeter. The proteins studied included: basic myelin protein (A1 protein), cytochrome c, major apoprotein of myelin proteolipid (N-2 apoprotein), gramicidin A, polylysine, ribonuclease and hemoglobin. The lipids used for the interactions were dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol. The interactions were grouped in three catagories each having very different effects on the phospholipid phase transition from solid to liquid crystalline. The calorimetric studies were also correlated with data from vesicle permeability and monolayer expansion. Ribonuclease and polylysine which exemplify group 1 interactions, show strong dependence on electrostatic binding. Their effects on lipid bilayers include an increase in the enthalpy of transition (deltaH) accompanied by either an increase or no change in the temperature of transition (Tc). In addition, they show minimal effects on vesicle permeability and monolayer expansion. It was concluded that these interactions represent simple surface binding of the protein on the lipid bilayer without penetration into the hydrocarbon region. Cytochrome c and A1 protein, which exemplify group 2 interactions, also show a strong dependence on the presence of net negative charges on the lipid bilayers for their binding. In contrast to the first group, however, they induce a drastic decrease in both Tc and deltaH of the lipid phase transition. Furthermore, they induce a large increase in the permeability of vesicles and a substantial expansion in area of closely packed monolayers at the air-water interface. It was concluded that group 2 interactions represent surface binding followed by partial penetration and/or deformation of the bilayer. Group 3 interactions, shown by proteolipid apoprotein and gramicidin A, were primarily non-polar in character, not requiring electrostatic charges and not inhibited by salt and pH changes. They had no appreciable effect on the Tc but did induce a linear decrease in the magnitude of the deltaH, proportional to the percentage of protein by weight. Membranes containing 50% proteolipid protein still exhibited a thermotropic transition with a deltaH one half that of the pure lipid, and only a small diminution of the size of the cooperative unit. It was concluded that in this case the protein was embedded within the bilayer, associating with a limited number of molecules via non-polar interactions, while the rest of the bilayer was largely unperturbed.  相似文献   

16.
The peptide sequence (175-192) RFPFHRCGAGPKLTKDLE (P59) of the E2 envelope protein of GB virus C (GBV-C) has been proved to decrease cellular membrane fusion and interfere with the HIV-1 infectivity in a dose-dependent manner. Based on these previous results, the main objective of this study was to deepen in the physicochemical aspects involved in this interaction. First, we analyzed the surface activity of P59 at the air-water interface as well as its interaction with zwitterionic or negatively charged lipid monolayers. Then we performed the same experiments with mixtures of P59/gp41-FP. Studies on lipid monolayers helped us to understand the lipid-peptide interaction and the influence of phospholipids on peptide penetration into lipid media. On another hand, studies with lipid bilayers showed that P59 decreased gp41-FP binding to anionic Large Unilamellar Vesicles. Results can be attributed to the differences in morphology of the peptides, as observed by Atomic Force Microscopy. When P59 and gp41-FP were incubated together, annular structures of about 200 nm in diameter appeared on the mica surface, thus indicating a peptide-peptide interaction. All these results confirm the gp41-FP-P59 interaction and thus support the hypothesis that gp41-FP is inhibited by P59.  相似文献   

17.
Summary The ability of native and chemically modified myelin basic protein to induce fusion of chicken erythrocytes and to interact with lipids in monolayers at the air-water interface and liposomes was studied. Chemical modifications of myelin basic protein were performed by acetylation and succinylation: the positive charges of the native protein were blocked to an extent of about 90–95%.Cellular aggregation and fusion of erythrocytes into multinucleated cells was induced by the native myelin basic protein. This effect was diminished for both acetylated and succinylated myelin basic protein. Native myelin basic protein penetrated appreciably in sulphatide-containing lipid monolayers while lower penetration occurred in monolayers of neutral lipids. Contrary to this, both chemically modified myelin basic proteins did not show any selectivity to penetrate into interfaces of neutral or negatively charged lipids. The intrinsic fluorescence of the native and chemically modified myelin basic proteins upon interacting with liposomes constituted by dipalmitoylphosphatidycholine, glycosphingolipids, egg phosphatidic acid or dipalmitoylphosphatidyl glycerol was studied. The interaction with liposomes of anionic lipids is accompanied by a blue shift of the maximum of the native protein emission fluorescence spectrum from 346 nm to 335 nm; no shift was observed with liposomes containing neutral lipids. The acetylated and succinylated myelin basic proteins did not show changes of their emission spectra upon interacting with any of the lipids studied. The results obtained in monolayers and the fluorescence shifts indicate a lack of correlation between the ability of the modified proteins to penetrate lipid interfaces and the microenvironment sensed by the tryptophan-containing domain.Abbreviations MBP myelin basic protein - DPPC dipalmitoyl phosphatidylcholine - DPPG dipalmitoyl phosphatidylglycerol - PA phosphatidic acid  相似文献   

18.
The monolayer technique has been used to study the interaction of lipids with plasma apolipoproteins. Apolipoprotein C-II and C-III from human very low density lipoproteins, apolipoprotein A-I from human high density lipoproteins and arginine-rich protein from swine very low density lipoproteins were studied. The injection of each apoprotein underneath a monolayer of egg phosphatidyl[14C]choline at 20 mN/m caused an increase in surface pressure to approximately 30 mN/m. With apolipoprotein C-II and apolipoprotein C-III there was a decrease in surface radioactivity indicating that the apoproteins were removing phospholipid from the interface; the removal of phospholipid was specific for apolipoprotein C-II and apolipoprotein C-III. Although there was a removal of phospholipid from the monolayer, the surface pressure remained constant and was due to the accumulation of apoprotein at the interface. The rate of surface radioactivity decrease was a function of protein concentration, required lipid in a fluid state and, of the lipids tested, was specific for phosphatidylcholine. Cholesterol and phosphatidylinositol were not removed from the interface. The addition of 33 mol% cholesterol to the phosphatidylcholine monolayer did not affect the removal of phospholipid by apolipoprotein C-III.The addition of phospholipid liposomes to the subphase greatly facilitated the apolipoprotein C-II-mediated removal of phospholipid from the interface.  相似文献   

19.
K Hong  V D Vacquier 《Biochemistry》1986,25(3):543-549
Lysin, a protein of Mr 16 000 from the acrosome granule of the abalone, is responsible for the dissolution of the egg vitelline layer. The primary structure of this cationic protein projects some hydrophobic domains in the secondary structure. Lysin was found to associate nonselectively with phospholipid bilayers and cause a spontaneous release of encapsulated carboxyfluorescein in liposomes. The association of lysin with phosphatidylcholine liposomes suggests that there is a hydrophobic interaction between lysin and lipid bilayers. Binding of lysin to phospholipid resulted in the aggregation of phosphatidylserine-containing liposomes, but aggregation was not observed in neutral phosphatidylcholine liposomes. Resonance energy transfer and dequenching of fluorescent 1-palmitoyl-2-cis-parinaroylphosphatidylcholine were both used to determine the fusogenic activity of lysin in aggregated liposomes. Results from both assays are consistent. Lysin-induced fusion was observed in all the phosphatidylserine-containing liposomes, and the general trend of fusion susceptibility was phosphatidylserine/phosphatidylcholine (1:2) approximately equal to phosphatidylserine/phosphatidylcholine/phosphatidylethanolamine (1:1:1) greater than phosphatidylserine/phosphatidylethanolamine (1:2). Cholesterol up to 30% did not affect the intrinsic fusion susceptibility. A hydrophobic penetration by protein molecules and the packing of phospholipid bilayers are used to interpret the fusion susceptibility. Lysin-induced liposome aggregation was highly independent of the state of self-association of lysin in ionic medium. However, the fusogenic activity of self-associated lysin was found to be much less than the monodispersed one. Liposomes preincubated with Ca2+ did not fuse initially as readily as those without Ca2+ treatment.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

20.
Lipid-protein interactions in reconstituted band 3 preparations were investigated by using spin-labeled lipids in conjunction with electron paramagnetic resonance (EPR) spectroscopy. Purified erythrocyte band 3 was reconstituted into egg phosphatidylcholine liposomes at high protein density with preservation predominantly of the dimeric state. Lipid-protein associations were revealed by the presence of a component in the EPR spectra that, when compared to spectra obtained from protein-free bilayers, indicated that lipid chain motions are restricted by interactions with the protein. From the fraction of the motionally restricted component obtained from the phosphatidylcholine spin-label, a value of 64 +/- 14 annular lipids per band 3 dimer was obtained. This agrees with a value of 62 for the number of lipids that may be accommodated around the electron density map of a band 3 dimer. Selectivity of various spin-labeled lipids for the protein revealed that androstanol had a lower affinity for the band 3 interface, whereas a distinct preference was observed for the negatively charged lipids phosphatidylglycerol and stearic acid over phosphatidylcholine. This preference for negatively charged lipids could not be screened by 1-M salt, indicating that electrostatic lipid-protein interactions are not dominant. Estimates of annular lipid exchange rates from measured acyl chain segmental motions suggested that the rate of exchange between bilayer and boundary lipids was approximately 10(6) s(-1), at least an order of magnitude slower than the rate of lipid lateral diffusion in protein-free bilayers.  相似文献   

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