Search

The microphase separation of lipid molecules on a vesicle membrane can be induced, depending on the difference in the geometric structures of their headgroups. Through cryo-transmission-electron-microscopy analysis, a lens-like vesicle was prepared by mixing 50 wt% Span 40 (sorbitan monopalmitate) and 50 wt% Tween 40 [polyoxyethylene (20) sorbitan monopalmitate]. Considering the molecular structures of Span 40 and Tween 40, the high-curvature region was mainly formed by Tween 40. As determined by Fourier-transform infrared spectroscopy, dielectric-dispersion analysis, and differential scanning calorimetry, a hydration layer was likely formed because polyoxyethylene conjugates with the headgroups of Tween 40. These investigations of the obtained self-assembled aggregates of nonionic surfactants with heterogeneous surfaces could contribute to the development of new types of biomaterials., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The adsorption behaviour of amyloid beta (Aβ), thought to be a key peptide for understanding Alzheimer's disease, was investigated by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Aβ aggregates depending on the lipid membrane condition though it has not been fully understood yet. In this study, Aβ samples on different lipid membranes, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were observed with ToF-SIMS and the complex ToF-SIMS data of the Aβ samples was interpreted using data analysis techniques such as principal component analysis (PCA), gentle-SIMS (G-SIMS) and g-ogram. DOPC and DMPC are liquid crystal at room temperature, while DPPC is gel at room temperature. As primary ion beams, Bi3(+) and Ar cluster ion beams were used and the effect of an Ar cluster ion for evaluating biomolecules was also studied. The secondary ion images of the peptide fragment ions indicated by G-SIMS and g-ogram were consistent with the PCA results. It is suggested that Aβ is adsorbed homogeneously on the liquid-crystalline-phase lipid membranes, while it aggregates along the lipid on the gel-phase lipid membrane. Moreover, in the results using the Ar cluster, the influence of contamination was reduced.

We have focused on the interaction between the Span 80 vesicle and phospholipid vesicle (liposome). The Span 80 vesicle was mixed with a phospholipid vesicle (liposome), used as a simplified model of plasma membrane. From calcein leakage experiments, it was revealed that the interaction between the Span 80 vesicles and the liposomes could perturb the liposome membrane. In the experiments based on fluorescence resonance energy transfer, the lipid mixing between Span 80 vesicle and liposome was observed. The above phenomena were also supported by the fluorescence spectroscopic analysis using laurdan, resulting in the variation in the membrane properties of liposome after its mixing with Span 80 vesicle. These results suggest that the Span 80 vesicles can easily interact and hemifuse with the liposome membrane, which depend on the membrane properties of the Span 80 vesicle, "flexible" and "molecular structure" of the components., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The growth of giant vesicles (GVs) can be considered as a consecutive process of swelling/detachment/deformation, which is a response of lipid membranes on solid surfaces to the solvent and environmental factors such as temperature and ionic strength. The electroformation method allows to visualize the responses to such factors. The additive effect of the protein on the growth of GVs, composed of zwitterionic phospholipids, was herein investigated using the electroformation method. Proteins denatured by a pH-shift (to be in the Molten Globule state) perturbed the lipid membranes, resulting in the acceleration of GV growth. The GVs detached from the electrode showed deformation close to a stomatocyte. It was revealed that common factor for the response of lipid membranes was the variation of the apparent area elastic modulus associated with the interaction between proteins and lipid membranes. The present finding affords better understanding about the response of lipid membranes on solid surfaces under a variety of environment factors., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Phospholipase C (PLC) is considered to be one of key enzymes for the design of drug delivery system using the endocytosis route, because PLC can catalyze the membrane fusion between cell membranes and phospholipid vehicles (liposomes). Membrane fusion by PLC was then studied under various pHs to model the endosomal environment. The used liposomes were composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and cholesterol (Ch). The membrane fusion was dominated by the enzymatic reaction at pH 6-7.5. In contrast, the membrane perturbation effect due to the conformational change of PLC could induce the membrane fusion at around pH 4. The maximal value of membrane fusion was observed at around pH 5 for three liposomes in the order of DOPC

The interaction between single-stranded RNAs and liposomes was studied using UV, Fourier Transform Infrared spectroscopy (FTIR) and Circular Dichroism spectroscopy (CD). The effect of the surface characteristics of liposomes, which were composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and modified with cholesterol (Ch) or 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), on the liposome-RNA interaction was investigated. The fluorescence of 6-(p-toluidino)naphthalene-2-sulfonate (TNS) embedded in the liposome surface (ε = 30-40) was decreased in the presence of tRNA, suggesting that single-stranded tRNA could bind onto the liposome. The dehydration of -PO₂⁻-, guanine (G) and cytosine (C) of tRNA molecules in the presence of liposomes suggested both an electrostatic interaction (phosphate backbone of tRNA and trimethylammonium group of POPC, DOTAP) and a hydrophobic interaction (guanine or cytosine of tRNA and aliphatic tail of lipid). The tRNA conformation on the liposome was determined by CD spectroscopy. POPC/Ch (70/30) maintained tRNA conformation without any denaturation, while POPC/DOTAP(70/30) drastically denatured it. The mRNA translation was evaluated in an Escherichia coli cell-free translation system. POPC/Ch(70/30) enhanced expression of green fluorescent protein (GFP) (116%) while POPC/DOTAP(70/30) inhibited (37%), suggesting that the conformation of RNAs was closely related to the translation efficiency. Therefore, single-stranded RNAs could bind to liposomal membranes through electrostatic and hydrophobic attraction, after which conformational changes were induced depending on the liposome characteristics.

In this study, we investigated the dynamics of a membrane interface of liposomes prepared by eight zwitterionic phosphatidylcholines in terms of their headgroup mobility, with spectroscopic methods such as dielectric dispersion analysis (DDA), fluorescence spectroscopy. The DDA measurement is based on the response of the permanent dipole moment to a driving electric field and could give the information on the axial rotational Brownian motion of a headgroup with the permanent dipole moment. This motion depended on kinds of phospholipids, the diameter of the liposomes, and the temperature. The activation energy required to overcome the intermolecular force between headgroups of phospholipids depended on the strength of the interaction between headgroups such as hydrogen bonds and/or dipole-dipole interaction. Hydration at the phosphorous group of phospholipid and the molecular order of lipid membrane impaired the interaction between headgroups. Furthermore, the hydrophobicity of membrane surface increased parallel to the increase in headgroup mobility. It is, therefore, concluded that hydration of headgroup promoted its mobility to make the membrane surface hydrophobic. The lipid membrane in liquid crystalline phase or the lipid membrane with the larger curvature was more hydrophobic., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The surface properties of Span 80 vesicles at various cholesterol contents, together with those of various liposomes, were characterized by using fluorescence probes. The membrane fluidity of the Span 80 vesicles was measured by 1,6-diphenyl-1.3.5-hexatriene (DPH) and trimethlyammonium-DPH (TMA-DPH), and the results suggested that the surface of the Span 80 vesicles was fluid due to the lateral diffusion of Span 80 molecules. The depolarization measured by TMA-DPH and the headgroup mobility measured by dielectric dispersion analysis indicated the high mobility of the head group of Span 80 vesicles. This suggested that the surface of Span 80 vesicles was flexible due to the head group structure of Span 80, sorbitol. In addition, spectrophotometric analysis with 6-dodecanoyl-N, N-dimethyl-2-naphthylamine and 8-anilino-1-naphthalenesulfonic acid indicated that the water molecules could easily invade into the interior of the Span 80 vesicle membrane, suggesting that the membrane surface was more wet than the liposome surface. These surface properties indicated that the protein could interact with the interior of vesicle membranes, which was similar to the case of cholesterol. Thus the present results confirmed that the Span 80 vesicle surfaces showed the unique characteristics of fluidity, flexibility, and "wetness", whereas the liposome surfaces did not., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The amyloid deposition of amyloid beta (Abeta) peptides is a critical pathological event in Alzheimer disease (AD). Preventing the formation of amyloid deposits and removing preformed fibrils in tissues are important therapeutic strategies against AD. Previously, we reported the destruction of amyloid fibrils of beta(2)-microglobulin K3 fragments by laser irradiation coupled with the binding of amyloid-specific thioflavin T. Here, we studied the effects of a laser beam on Abeta fibrils. As was the case for K3 fibrils, extensive irradiation destroyed the preformed Abeta fibrils. However, irradiation during spontaneous fibril formation resulted in only the partial destruction of growing fibrils and a subsequent explosive propagation of fibrils. The explosive propagation was caused by an increase in the number of active ends due to breakage. The results not only reveal a case of fragmentation-induced propagation of fibrils but also provide insights into therapeutic strategies for AD.

The inhibition of fibril formation of amyloid beta proteins (A beta) would be attractive therapeutic targets for the treatment of Alzheimer's disease (AD). Dopamine (DA) and other catechol derivatives were used as inhibitory factors for A beta fibril formation. The fibril formation of A beta was monitored by Thioflavin T fluorescence, a transmission electron microscopy (TEM) and a total internal reflection fluorescence microscopy (TIRFM). Catechol and its derivatives showed the dose-dependent inhibitory effects on the spontaneous A beta fibril formation. The inhibitory activity depended on the chemical structure of catechol derivatives both in the presence and absence of the liposome a model of biomembrane. Formation of catechol quinone-conjugated-A beta adduct by a Schiff-base is a key step for the inhibition effect of A beta fibril formation., ((c) 2009 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

The strategy to prepare a novel biocatalyst by the immobilization of chitosanase onto liposome (ICL) was carried out based on the direct interaction of liposomes with cell membrane of Streptomyces griseus cell. The ICL was characterized in relation to the molecular weight of protein, the chitosanase activity, the effect of the surface hydration of various liposomes on hydrolysis activity of immobilized chitosanase and the stability of ICL under various extreme conditions. The SDS-PAGE analysis of the purified ICL sample shows the existence of a protein with approximately 39kDa that corresponded to the sum of weight of the mature chitosanase and its signal peptide (38.8kDa). The above protein of ICL also expresses the chitosanase activity that is significantly higher than that of the conventional chitosanase. Furthermore, the surface hydration of liposomes used to prepare ICL that affected the activity of immobilized chitosanase verified the importance of liposome surfaces. Indeed, the stability of ICL assayed by measuring the chitosanase activity is significantly higher than that of conventional chitosanase under various temperatures and pH conditions. These characteristics of ICL show the possible preparation of the biocatalysts that can be prepared by immobilizing enzymes onto liposome vesicles properly.

The interaction between the neutral 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes and cell membrane of Streptomyces griseus induced by the heat treatment at specific temperature was investigated, focusing on the internalization of the neutral POPC liposomes with S. griseus cells. In an attempt to clarify the modes of liposome internalization, various kinds of inhibitors of endocytotic pathways were used to treat S. griseus cells. The efficiency of the heat treatment on liposome-cell membrane interactions was finally characterized based on the hydrophobic, electrostatic interactions and hydration effect. In fact, the internalization of the neutral liposomes into these cells was found to show higher rate and greater amount at higher temperatures. The kinetic study showed that the maximum amount of the internalized liposomes was, respectively, 469 x 10(5) and 643 x 10(5) liposomes/cell at 37 and 41 degrees C. The internalization of the neutral liposomes induced by the heat treatment was characterized, implying that the endocytosis occurred. The interactions involving the internalization, adsorption, and fusion of these liposomes with S. griseus cells were mainly contributed by the hydrophobic interaction and the unstable hydrogen bonds caused by the loss of water of surface hydration of cell membrane rather than the electrostatic interaction under the specific heat condition.

Arsenate is one of the most poisonous elements for living cells. When cells are exposed to arsenate, their life activities are immediately affected by various biochemical reactions, such as the binding of arsenic to membranes and the substitution of arsenic for phosphate or the choline head of phospholipids in the biological membranes. The effects of arsenate on the life activities of algae Chlorella vulgaris were investigated at various concentrations and exposure times. The results demonstrated that the living activities of algal cells (10(10)cells/L) were seriously affected by arsenate at a concentration of more than 7.5mg As/L within 24h. Algal cells and the artificial membranes (liposomes) were exposed to arsenate to evaluate its effects on the membrane fluidization. In the presence of arsenate, the membranes were fluidized due to the binding and substitution of arsenate groups for phosphates or the choline head on the their membrane surface. This fluidization of the biological membranes was considered to enhance the transport of toxicants across the membrane of algal cells.

An antioxidative liposome catalysis that mimics both superoxide dismutase (SOD) and peroxidase (POD) activities has been developed by using the liposomes modified with lipophilic Mn-(5,10,15,20-tetrakis[1-hexadecylpyridium-4-yl]-21H,23H-porphyrin) (Mn-HPyP). The SOD- and POD-like activities of the Mn-HPyP-modified liposome were first investigated by varying the type of phospholipid, such as 1,2-distearyl-sn-glycero-3-phosphocholine (DSPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC). Higher SOD-like activity was obtained in the case of DLPC and DMPC liposomes, in which the ligands were well-dispersed on the membrane in the liquid crystalline phase. The POD-like activity was maximal in the case of DMPC liposome, in which the Mn-HPyP complex was appropriately clustered on the membrane in the gel phase. On the basis of the above results, the co-induction of the SOD and POD activities to eliminate the superoxide and also hydrogen peroxide as a one-pot reaction was finally performed by using the Mn-HPyP-modified DMPC liposome, resulting in an increase in the efficiency of the elimination of both superoxide and hydrogen peroxide.

The peptide fragment of H2O2-treated Cu,Zn-superoxide dismutase (SOD) was found to be reactivated with liposomes prepared by 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The fragmentation of SOD was observed by 2 mM H2O2 treatment as well as by SOD inactivation and the loss of an alpha-helix in the neighborhood of its activity center. The H2O2-treated SOD, which lost its activity at different incubation times, was dramatically reactivated only by adding POPC liposomes, resulting in 1.3-2.8 times higher enzymatic activity. The ultrafiltration analysis of H2O2-treated SOD co-incubated with liposomes shows that some specific peptide fragments of the oxidized SOD can interact with POPC liposomes. A comparison of the fractions detected in reverse-phase chromatography shows that specific SOD fragments are able to contribute to the reactivation of oxidized and fragmented SOD in the presence of POPC liposomes. The liposomes can recruit the potentially active fragment of SOD among the lethally damaged SOD fragments to elucidate the antioxidative function.

Based on a number of experiments it is concluded that the fluorescein labeled beta-heptapeptide fluoresceinyl-NH-CS-(S)-beta(3)hAla-(S)-beta(3)hArg-(R)-beta(3)hLeu-(S)-beta(3)hPhe-(S)-beta(3)hAla-(S)-beta(3)hAla-(S)-beta(3)hLys-OH translocates across lipid vesicle bilayers formed from DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine). The conclusion is based on the following observations: (i) addition of the peptide to the vicinity of micrometer-sized giant vesicles leads to an accumulation of the peptide inside the vesicles; (ii) if the peptide is injected inside individual giant vesicles, it is released from the vesicles in a time dependent manner; (iii) if the peptide is encapsulated within sub-micrometer-sized large unilamellar vesicles, it is released from the vesicles as a function of time; (iv) if the peptide is submitted to immobilized liposome chromatography, the peptide is retained by the immobilized DOPC vesicles. Furthermore, the addition of the peptide to calcein-containing DOPC vesicles does not lead to significant calcein leakage and vesicle fusion is not observed. The finding that derivatives of the beta-heptapeptide (S)-beta(3)hAla-(S)-beta(3)hArg-(R)-beta(3)hLeu-(S)-beta(3)hPhe-(S)-beta(3)hAla-(S)-beta(3)hAla-(S)-beta(3)hLys-OH can translocate across phospholipid bilayers is supported by independent measurements using Tb(3+)-containing large unilamellar vesicles prepared from egg phosphatidylcholine and wheat germ phosphatidylinositol (molar ratio of 9:1) and a corresponding peptide that is labeled with dipicolinic acid instead of fluorescein. The experiments show that this dipicolinic acid labeled beta-heptapeptide derivative also permeates across phospholipid bilayers. The possible mechanism of the translocation of the particular beta-heptapeptide derivatives across the membrane of phospholipid vesicles is discussed within the frame of the current understanding of the permeation of certain oligopeptides across simple phospholipid bilayers.