Interaction of the 43K protein with components of Torpedo postsynaptic membranes

Interactions of the major Mr 43 000 peripheral membrane protein (43K protein) with components of Torpedo postsynaptic membranes have been examined. Treatment of membranes with copper o-phenanthroline promotes the polymerization of 43K protein to dimers and higher oligomers. These high molecular weight forms of 43K protein can be converted to monomers by reduction with dithiothreitol and do not contain any of the other major proteins found in these membranes, including the subunits of the acetylcholine receptor, as shown by immunoblotting with monoclonal antibodies. To study directly its interactions with the membrane, the 43K protein was radioiodinated and purified by immunoaffinity chromatography. Purified 43K protein binds tightly to pure liposomes of various compositions in a manner that is not inhibited by KCl concentrations up to 0.75 M. The binding can be reversed by adjusting the pH of the reaction to 11, the same treatment that removes 43K protein from postsynaptic membranes. Unlabeled 43K protein solubilized from Torpedo membranes with cholate can be reconstituted with exogenously added lipids in the absence of the receptor. The results suggest that 43K protein molecules are amphipathic and that they may interact with each other and with the lipid bilayer. These interactions cannot explain the coextensive distribution of 43K proteins with acetylcholine receptors in situ. However, they could account for the association of the 43K protein with the postsynaptic membrane and may contribute to the maintenance of the structure of the cytoplasmic specialization of which this protein is a major component.     

Interaction of non-steroidal antiestrogens with dopamine receptor binding

The ability of various estrogen antagonists and agonists to compete with [3H]spiroperidol, [3H]domperidone, [3H]dihydroalprenolol, [3H]dihydroergocryptine, [3H]dopamine or [3H]5-hydroxytryptamine for binding to membrane preparations from rat brain tissue was tested. The non-steroidal triphenylethylene-type antiestrogens with an amine side chain--enclomiphene, nitromifene, tamoxifen and zuclomiphene--were found to be competitive inhibitors of [3H]spiroperidol (Kd = 0.12 nM; Bmax = 101 fmol/mg protein) and [3H]domperidone (Kd = 0.62 nM; Bmax = 86 fmol/mg protein) binding to striatal membranes. The Ki values ranged from 4-12 microM. Estradiol-17 beta (Ki = 480 microM) or diethylstilbestrol (Ki = 63 microM) were much less effective inhibitors exhibiting noncompetitive interaction with the in vitro binding of [3H]spiroperidol. The pharmacological relevance of the antiestrogen interactions with dopamine receptor binding is discussed with respect to adverse effects of the in vivo administered compounds such as nausea and vomiting.     

Interaction of the pitavastatin with model membranes

Pitavastatin is a statin drug that, by competitively inhibiting 3-hydroxy-3-methylglutaryl-coenzyme A reductase, can lower serum cholesterol levels of low-density lipoprotein (LDL) accompanied by side effects due to pleiotropic effects leading to statin intolerance. These effects can be explained by the lipophilicity of statins, which creates membrane affinity and causes statin localization in cellular membranes. In the current report, the interaction of pitavastatin with POPC model membranes and its influence on the membrane structure were investigated using ¹H, ²H and ³¹P solid-state NMR spectroscopy. Our experiments show the average localization of pitavastatin at the lipid/water interface of the membrane, which is biased towards the hydrocarbon core in comparison to other statin molecules. The membrane binding of pitavastatin also introduced an isotropic component into the ³¹P NMR powder spectra, suggesting that some of the lamellar POPC molecules are converted into highly curved structures.     

Interaction of ferredoxin:NADP oxidoreductase with model membranes

The ferredoxin:NADP⁺ oxidoreductase (FNR) is a plant enzyme, catalyzing the last step of photosynthetic linear electron transport, and involved also in cyclic electron transport around photosystem I. In this study we present the first evidence of FNR (isolated from spinach and from wheat) interaction directly with a model membrane without the mediation of any additional protein. The monomolecular layer technique measurements showed a significant increase in surface pressure after the injection of enzyme solution beneath a monolayer consisting of chloroplast lipids: monogalactosyldiacylglycerol or digalactosyldiacylglycerol. An ATR FTIR study revealed also the presence of FNR in a bilayer composed of these lipids. The secondary structure of the protein was significantly impaired by lipids, as with a pH-induced shift. The stabilization of FNR in the presence of lipids leads to an increase in the rate of NADPH-dependent reduction of dibromothymoquinone catalyzed by the enzyme. The biological significance of FNR-membrane interaction is discussed.     

Interaction of furosemide with lipid membranes

Summary The interaction of furosemide with different phospholipids was investigated. Its influence on the lipid structure was inferred from its effect on the phase transition properties of lipids and on the conductance of planar bilayer membranes. The thermotropic properties of dipalmitoyl phosphatidylcholine, phosphatidylethanolamine (natural), dipalmitoyl phosphatidylethanolamine, brain sphingomyelin, brain cerebrosides and phosphatidylserine in the presence and absence of furosemide were investigated by differential scanning calorimetry,. The modifying effect of furosemide seems to be strongest on phosphatidylethanolamine (natural) and sphingomyelin bilayers. The propensity of furosemide to decrease the electrical resistance of planar lipid membranes was also studied and it is shown that the drug facilitates the transport of ions. Partition coefficients of furosemide between lipid bilayers and water were measured.Abbreviations DSC differential scanning calorimetry - PLM planar lipid membranes - DPPC dipalmitoyl phosphatidylcholine - DMPC dimyristoyl phosphatidylcholine - PE phosphatidyl ethanol     

Interaction of RNA with phospholipid membranes

RNAs binding with liposomes under near physiological conditions were obtained by molecular selection. Structural analysis showed that the RNAs could form complexes owing to complementary sequences located in loops. Oligomerization of the RNAs selected was experimentally confirmed. The results and published data testified that formation of high-molecular-weight complexes is a major mechanism increasing the RNA affinity for phospholipid membranes. The role of RNA-membrane interactions in early evolution is discussed in terms of the RNA world hypothesis.     

Interaction of synapsin I with membranes

The synapsins (I, II, and III) comprise a family of peripheral membrane proteins that are involved in both regulation of neurotransmitter release and synaptogenesis. Synapsins are concentrated at presynaptic nerve terminals and are associated with the cytoplasmic surface of synaptic vesicles. Membrane-binding of synapsins involves interaction with both protein and lipid components of synaptic vesicles. Synapsin I binds rapidly and with high affinity to liposomes containing anionic lipids. The binding of bovine synapsin I to liposomes was studied using fluoresceinphosphatidyl-ethanolamine (FPE) to measure membrane electrostatic potential. Synapsin binding to liposomes caused a rapid increase in FPE fluorescence, indicating an increase in positive charge at the membrane surface. Synapsin I binding to monolayers resulted in a substantial increase in monolayer surface pressure. At higher initial surface pressures, the synapsin-induced increase in monolayer surface pressure is dependent on the presence of anionic lipids in the monolayer. Synapsin I also induced rapid aggregation of liposomes, but did not induce leakage of entrapped carboxyfluorescein, while other aggregation-inducing agents promoted extensive leakage. These results are in agreement with the presence of amphipathic stretches of amino acids in synapsin I that exhibit both electrostatic and hydrophobic interactions with membranes, and offer a molecular explanation for the high affinity binding of synapsin I to liposomes and for stabilization of membranes by synapsin I.     

Interaction of ethanol with biological membranes

Ethanol is among the drugs with anesthetic potency determined by lipid solubility, in accord with the Meyer-Overton hypothesis. Thus, it is likely that ethanol acts in a hydrophobic environment. Using electron paramagnetic resonance with 5-doxylstearic acid as spin label, we find that ethanol disorders mouse cell membranes, making the lipid matrix more fluid. We surmise that consequent disruption of the function of integral membrane proteins may be the cause of ethanol's central actions. When mice are treated for 8 days with ethanol, their membranes become tolerant to the disordering effect of ethanol. This tolerance is accompanied by an increased proportion of cholesterol in the membranes.     

Interaction of insecticides with lipid membranes

The permeability of liposome membranes is increased by organophosphorus and organochlorinated insecticides at concentrations of 10⁻⁵−10⁻⁴ M. The order of effectiveness is similar to the toxicity of the compounds to mammals, and is the following for permeation of non-electrolytes and for valinomycin-induced permeation of K⁺: parathion > 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT) ≈ aldrin malathion > lindane. The degree of effectiveness for X-537A-induced permeation of Ca²⁺ was the following: aldrin DDT > parathion malathion > lindane. The organophosphorus compound, ethyl azinphos (10⁻⁴ M), dramatically increases the permeability of liposome membranes to all the tested substances, probably as a consequence of surfactant effects. Some organochlorinated insecticides appear to react with cation ionophores and modulate their motion across lipid membranes.It is suggested that the insecticides may exert some of their toxic actions by modifying certain mechanisms in the cell membrane.     

Interaction of chlorpromazine with phospholipid membranes

The interaction of chlorpromazine (CPZ) with artificial membranes (egg-yolk phosphatidylcholine liposomes) has been studied. Measurements of the surface electric potential, which is modified in the presence of the ionized form of the drug, were obtained by electron paramagnetic resonance spectroscopy (EPR) using a positively charged amphiphilic spin-probe. This probe partitions between the aqueous and lipidic phases depending on the surface potential and on the structural state of the membrane. The surface potential was measured as a function of drug concentration in the range where the spectral line-shapes are not affected by the incorporation of the drug. From these experimental results and through an appropriate formalism we obtain information on the binding of the drug to the lipid bilayer and on the ionization of the drug in the lipidic phase. Correspondence to: C. Anteneodo     

Interaction of benzocaine with model membranes

We measured the absorption properties, water solubility and partition coefficients (P) between n-octanol, egg phosphatidylcholine (EPC) liposomes and erythrocyte ghosts/water for benzocaine (BZC), an ester-type always uncharged local anesthetic. The interaction of BZC with EPC liposomes was followed using Electron Paramagnetic Resonance, with spin labels at different positions in the acyl chain (5, 7, 12, 16-doxylstearic acid methyl ester). Changes in lipid organization upon BZC addition allowed the determination of P values, without phase separation. The effect of BZC in decreasing membrane organization (maximum of 11.6% at approx. 0.8:1 BZC:EPC) was compared to those caused by the local anesthetics tetracaine and lidocaine. Hemolytic tests revealed a biphasic (protective/inductive) concentration-dependent hemolytic effect for BZC upon rat erythrocytes, with an effective BZC:lipid molar ratio in the membrane for protection (RePROT), onset of hemolysis (ReSAT) and 100% membrane solubilization (ReSOL) of 1.0:1, 1.1:1 and 1.3:1, respectively. The results presented here reinforce the importance of considering hydrophobic interactions in the interpretation of the effects of anesthetics on membranes.     

PMR studies of phosphatidylcholine-cholesterol vesicles interacting with lucensomycin.

Spin-lattice relaxation times (T1) were measured above the phase transition temperature on sonicated vesicles of egg- or dipalmitoyl-phosphatidylcholine containing cholesterol and/or the polyenic antibiotic, lucensomycin. T1 values of only the terminal methyl groups of the fatty acyl chains were significantly reduced by cholesterol. Lucensomycin caused, more markedly in cholesterol-containing vesicles, a selective reduction of the T1 values of the N-methyl groups. An even more conspicuous decrease, occurring only in cholesterol-containing vesicles, was observed for the transverse relaxation times (T2) of the N-methyl signals upon addition of lucensomycin. The polyene failed to remove the well-known broadening effect of cholesterol on phosphatidylcholine methylene signals. These results indicate that as lucensomycin binds to cholesterol-containing membranes, there is a detectable perturbation of the dynamic structure of the N-methyl groups with an increase in the degree of motional anisotropy. But the non-polar region of the bilayer seems not significantly perturbed by the polyene.     

Interaction of smooth muscle plasma membranes with flat lipid membranes

The method of implantation of smooth muscle cells from plasma membranes (PM) of the rabbit intestine into flat lipid membranes (FLM) is described. The method is based on the pretreatment of PM vesicles with asolectin liposomes in the ratio that provides the activation of membrane ATPases. Thus modified FLM possesses channel conductivity.     

Interaction of a mitochondrial presequence with lipid membranes: role of helix formation for membrane binding and perturbation

The binding of a peptide to a biological membrane is often accompanied by a transition from a random coil structure to an amphipathic alpha-helix. Recently, we have presented a new approach which allows the determination of the thermodynamic parameters of membrane-induced helix formation [Wieprecht et al. (1999) J. Mol Biol. 294, 785]. It involves a systematic variation of the helix content of a given peptide by double D-substitution and a correlation of the binding parameters with the helicity. Here we have used this method to study membrane-induced helix formation for the presequence of rat mitochondrial rhodanese (RHD). The thermodynamic parameters of binding of the peptide RHD and of four of its double D-isomers were determined for 30 nm (SUVs) and 100 nm (LUVs) unilamellar vesicles composed of phosphatidylcholine/phosphatidylglycerol (3:1) using circular dichroism spectroscopy, fluorescence spectroscopy, and isothermal titration calorimetry. The incremental changes of the thermodynamic parameters of helix formation were found to be very similar for SUVs and LUVs. Membrane-induced helix formation of RHD entailed a negative enthalpy of Delta H(helix) = -0.5 to -0.6 kcal/mol/residue and was opposed by an entropy of about Delta S(helix) = -1 to -1.4 cal/mol K/residue. The free energy of helix formation, Delta G(helix), was about -0.2 kcal/mol, and helix formation accounted for 50-60% of the total free energy of membrane binding. Dye-release experiments were used to assess the role of helix formation for the membrane perturbation potential of the peptides. While helix formation plays a major role for membrane binding, it appears to have little importance for inducing membrane leakiness.     

Interaction of cardiotoxins with membranes: a molecular modeling study

Incorporation of beta-sheet proteins into membrane is studied theoretically for the first time, and the results are validated by the direct experimental data. Using Monte Carlo simulations with implicit membrane, we explore spatial structure, energetics, polarity, and mode of insertion of two cardiotoxins with different membrane-destabilizing activity. Both proteins, classified as P- and S-type cardiotoxins, are found to retain the overall "three-finger" fold interacting with membrane core and lipid/water interface by the tips of the "fingers" (loops). The insertion critically depends upon the structure, hydrophobicity, and electrostatics of certain regions. The simulations reveal apparently distinct binding modes for S- and P-type cardiotoxins via the first loop or through all three loops, respectively. This rationalizes an earlier empirical classification of cardiotoxins into S- and P-type, and provides a basis for the analysis of experimental data on their membrane affinities. Accomplished with our previous simulations of membrane alpha-helices, the computational method may be used to study partitioning of proteins with diverse folds into lipid bilayers.     

Interaction of lambda bacteriophages with mammalian cells. II. Elucidation of the role of interacting components

The study of 3H-thymidine labelled bacteriophage lambda C185757 uptake by HeLa, RH and Chinese hamster cell revealed the lack of cells or phage specificity in the phage interaction with cells. The phage uptake is shown to be an active process depending on the cell state. The mechanism of "protective" action of calcium chloride is found to be as follows: the calcium phosphate precipitate formed in phosphate-containing media absorbs the phage, thus increasing its concentration on the cell surface, which makes the pinocytosis more effective.     

Interaction of liposomes with black lipid membranes

Liposomes labelled with fluorescent pigments were allowed to interact with black lipid films. The transfer of label from the liposomes to the film was studied by fluorescence and photoelectric measurements. With the neutral lipid lecithin, in contrast to negatively charged phosphatidylinositol, a rapid transfer was observed. The results are discussed with respect to fusion of liposomes with black lipid films.     

Interaction of octyl-beta-thioglucopyranoside with lipid membranes.

Octyl-beta-thioglucopyranoside (octyl thioglucoside, OTG) is a nonionic surfactant used for the purification, reconstitution, and crystallization of membrane proteins. The thermodynamic properties of the OTG-membrane partition equilibrium are not known and have been investigated here with high-sensitivity titration calorimetry. The critical concentration for inducing the bilayer <==> micelle transition was determined as cD* = 7.3 mM by 90 degree light scattering. All thermodynamic studies were performed well below this limit. Sonified, unilamellar lipid vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with and without cholesterol were employed in the titration calorimetry experiments, and the temperature was varied between 28 degrees C and 45 degrees C. Depending on the surfactant concentration in the membrane, the partition enthalpy was found to be exothermic or endothermic, leading to unusual titration patterns. A quantitative interpretation of all titration curves was possible with the following model: 1) The partitioning of OTG into the membrane follows a simple partition law, i.e., Xb = Kc(D,f), where Xb denotes the molar amount of detergent bound per mole of lipid and c(D,f) is the detergent concentration in bulk solution. 2) The partition enthalpy for the transfer of OTG from the aqueous phase to the membrane depends linearly on the mole fraction, R, of detergent in the membrane. All calorimetric OTG titration curves can be characterized quantitatively by using a composition-dependent partition enthalpy of the form deltaHD(R) = -0.08 + 1.7 R (kcal/mol) (at 28 degrees C). At low OTG concentrations (R < or = 0.05) the reaction enthalpy is exothermic; it becomes distinctly endothermic as more and more surfactant is incorporated into the membrane. OTG has a partition constant of 240 M(-1) and is more hydrophobic than its oxygen-containing analog, octyl-beta-D-glucopyranoside (OG). Including a third nonionic amphiphile, octa(ethyleneoxide) dodecylether (C12EO8), an empirical relation can be established between the Gibbs energies of membrane partitioning, deltaGp, and micelle formation, deltaGmic, with deltaGp = 1.398 + 0.647 deltaGmic (kcal/mol). The partition constant of OTG is practically independent of temperature and of the cholesterol content of the membrane. In contrast, the partition enthalpy shows a strong temperature dependence. The molar specific heat capacity of the transfer of OTG from the aqueous phase to the membrane is deltaCp = -98 cal/(mol x K). The OTG partition enthalpy is also dependent on the cholesterol content of the membrane. It increases by approximately 1 kcal/mol at 50 mol% cholesterol. As the partition constant remains unchanged, the increase in enthalpy is compensated for by a corresponding increase in entropy, presumably caused by a restructuring of the membrane hydration layer.