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The formation of membrane vesicles is a common feature in all eukaryotes. Lipid rafts are the best-studied example of membrane domains for both eukaryotes and prokaryotes, and their existence also is suggested in Archaea membranes. Lipid rafts are involved in the formation of transport vesicles, endocytic vesicles, exocytic vesicles, synaptic vesicles and extracellular vesicles, as well as enveloped viruses. Two mechanisms of how rafts are involved in vesicle formation have been proposed: first, that raft proteins and/or lipids located in lipid rafts associate with coat proteins that form a budding vesicle, and second, vesicle budding is triggered by enzymatic generation of cone-shaped ceramides and inverted cone-shaped lyso-phospholipids. In both cases, induction of curvature is also facilitated by the relaxation of tension in the raft domain. In this Review, we discuss the role of raft-derived vesicles in several intracellular trafficking pathways. We also highlight their role in different pathways of endocytosis, and in the formation of intraluminal vesicles (ILVs) through budding inwards from the multivesicular body (MVB) membrane, because rafts inside MVB membranes are likely to be involved in loading RNA into ILVs. Finally, we discuss the association of glycoproteins with rafts via the glycocalyx.

Intraluminal vesicles (ILVs) are released into the extracellular space as exosomes after the fusion of multivesicular bodies (MVBs) with the plasma membrane. miRNAs are delivered to the raft-like region of MVB by RNA-binding proteins (RBPs). RNA loading into exosomes can be either through direct interaction between RNA and the raft-like region of the MVB membrane, or through interaction between an RBP&ndash, RNA complex with this raft-like region. Selection of RNA aptamers that bind to lipid raft region of liposomal membranes was performed using the selection-amplification (SELEX) method. The pool of RNA aptamers was isolated, and the binding of this pool to lipid-raft regions was demonstrated. Sequencing of clones from rafted liposome-eluted RNAs showed sequences apparently of independent origin. Bioinformatics analysis revealed the most frequent raft-motifs present within these sequences. Four raft RNA motifs, one of them an EXO motif, have been identified. These motifs appear to be most frequent both in the case of raft RNA aptamers and in the case of exosomal pro-tumoral miRNAs transferred from cancer cells to macrophages, natural killer cells and dendritic cells, thus suggesting that the selection for incorporation of these miRNAs into ILVs is based on their affinity to the raft-like region of the MVB membrane.

RNA motifs may promote interactions with exosomes (EXO-motifs) and lipid rafts (RAFT-motifs) that are enriched in exosomal membranes. These interactions can promote selective RNA loading into exosomes. We quantified the affinity between RNA aptamers containing various EXO- and RAFT-motifs and membrane lipid rafts in a liposome model of exosomes by determining the dissociation constants. Analysis of the secondary structure of RNA molecules provided data about the possible location of EXO- and RAFT-motifs within the RNA structure. The affinity of RNAs containing RAFT-motifs (UUGU, UCCC, CUCC, CCCU) and some EXO-motifs (CCCU, UCCU) to rafted liposomes is higher in comparison to aptamers without these motifs, suggesting direct RNA-exosome interaction. We have confirmed these results through the determination of the dissociation constant values of exosome-RNA aptamer complexes. RNAs containing EXO-motifs GGAG or UGAG have substantially lower affinity to lipid rafts, suggesting indirect RNA-exosome interaction via RNA binding proteins. Bioinformatics analysis revealed RNA aptamers containing both raft- and miRNA-binding motifs and involvement of raft-binding motifs UCCCU and CUCCC. A strategy is proposed for using functional RNA aptamers (fRNAa) containing both RAFT-motif and a therapeutic motif (e.g., miRNA inhibitor) to selectively introduce RNAs into exosomes for fRNAa delivery to target cells for personalized therapy.

In mammals, polysialic acid (polySia) attached to a small number of transmembrane protein carriers occurs on the surface of plasma membranes of neural, cancer, immune, and placental trophoblast cells. Here, our goal was to demonstrate the presence of polySia on exosomes and its effect on membrane properties. We isolated exosomes and found that polysialylated exosomes in fetal bovine serum originate mostly from placental trophoblasts, while in calf bovine serum, they originate from immune cells. Enzymatic removal of polySia chains from the exosomal surface makes the membrane surface potential more positive, transmembrane potential more negative, and reduces the activation energy for membrane anisotropy changes. We demonstrate for the first time that exosomes could interact through polySia–raft interactions. We suggest that polysialylation of exosomal membrane can have a thermo‐protecting effect and can modulate exosome–plasma membrane interactions.

We have studied the interaction of a VegT mRNA localization signal sequence with the membranes of the mitochondrial cloud in Xenopus oocytes, and the binding of the VegT mRNA signal sequence to the lipid raft regions of the vesicles bounded by ordered and disordered phospholipid bilayers. RNA preference for the membranes of the mitochondrial cloud was confirmed using microscopy of a fluorescence resonance energy transfer from RNA molecules to membranes. Our studies show that VegT mRNA has a higher affinity for ordered regions of lipid bilayers. This conclusion is supported by the dissociation constant measurements for RNA-liposome complex and the visualization of the FRET signal between giant vesicles and RNA. Our data indicate that these affinities are sensitive and distinct to the location of the localization elements within the VegT mRNA localization signal structure. Therefore, specific binding of VegT mRNA localization signal sequence to membranes can be responsible for polarized distribution of VegT mRNA in Xenopus oocytes. We suggest that the mechanism of this binding can involve the interaction of the localization elements within the VegT mRNA signal sequence with lipid raft regions of the mitochondrial cloud membranes, thereby utilizing localization elements as novel lipid raft-binding RNA motifs.

The distribution of amyloid beta peptide 42 (Aβ42) between model exosomal membranes and a buffer solution was measured. The model membranes contained liquid-ordered regions or phosphatidylserine. Results demonstrated that up to ca. 20% of amyloid peptide, generated in the plasma (or intracellular) membrane as a result of proteolytic cleavage of amyloid precursor proteins by β- and γ-secretases, can stay within the membrane milieu. The selection of RNA aptamers that bind to Aβ42 incorporated into phosphatidylserine-containing liposomal membranes was performed using the selection-amplification (SELEX) method. After eight selection cycles, the pool of RNA aptamers was isolated and its binding to Aβ42-containing membranes was demonstrated using the gel filtration method. Since membranes can act as a catalytic surface for Aβ42 aggregation, these RNA aptamers may inhibit the formation of toxic amyloid aggregates that can permeabilize cellular membranes or disrupt membrane receptors. Strategies are proposed for using functional exosomes, loaded with RNA aptamers specific to membrane Aβ42, to reduce the oxidative stress in Alzheimer’s disease and Down’s syndrome.

The function of human nervous system is critically dependent on proper interneuronal communication. Exosomes and other extracellular vesicles are emerging as a novel form of information exchange within the nervous system. Intraluminal vesicles within multivesicular bodies (MVBs) can be transported in neural cells anterogradely or retrogradely in order to be released into the extracellular space as exosomes. RNA loading into exosomes can be either via an interaction between RNA and the raft-like region of the MVB limiting membrane, or via an interaction between an RNA-binding protein-RNA complex with this raft-like region. Outflow of exosomes from neural cells and inflow of exosomes into neural cells presumably take place on a continuous basis. Exosomes can play both neuro-protective and neuro-toxic roles. In this review, we characterize the role of exosomes and microvesicles in normal nervous system function, and summarize evidence for defective signaling of these vesicles in disease pathogenesis of some neurodegenerative diseases.

Background: Pain, fear, depression often accompany patients as complications after stroke. They can usually take the shape of patients’ defensive reaction, who must struggle with physical and psychical consequences of stroke. Degree of those feelings’ intensity and the reactions related to them are indi-vidual for every patient.Aim of the study: The aim of the research was to determine the effect of post-stroke pain on the daily functioning of the patient and determine whether anxiety and depression determine the effects of treatment and return to activities of daily living after stroke.Material and methods: Research instruments were: an author’s questionnaire and the research scales (SOPL, Lawton’s IADL Scale, Katz Index and Doloplus Pain Scale). The study sample consisted of 31 patients from the Rehabilitation Department in Saint Roch Hospital in Ozimek. The research was carried out from October 2013 to March 2014. Results: The feeling of the fear and depressed appeared among 41.93% (13) patients and it was in the limit of normality. Symptoms of depression appeared among 6% (2) of respondents. The pain occurred among 90% (28) of patients, however, in the opinion of the patients did not constitute a serious obstacle to the continuation of the rehabilitation and daily functioning. The Katz Index revealed that 58% (18) of the patients did not need help with basic activities of daily life.Conclusions: Pain, anxiety, and depression had no significant effect on the course of the rehabilitation of patients in the study group. The pain did not decrease significantly physical activity. Potential problems with the daily functioning of patients through the process of rehabilitation, have been largely eliminated.

Polysialic acid (polySia) forms linear chains which are usually attached to the external surface of the plasma membrane mainly through the Neural Cell Adhesion Molecule (NCAM) protein. It is exposed on neural cells, several types of cancer cells, dendritic cells, and egg and sperm cells. There are several lipid raft-related phenomena in which polySia is involved; however the mechanisms of polySia action as well as determinants of its localization in lipid raft microdomains are still unknown, although the majority of NCAM molecules in the liquid-ordered raft membrane fractions of neural cells appear to be polysialylated. Here we investigate the affinity of polySia (both soluble and NCAM-dependent plasma membrane-bound) for liquid-ordered- and liquid-disordered regions of lipid vesicle and neuroblastoma cell membranes. Our studies indicate that polySia chains have a higher affinity for ordered regions of membranes as determined by the dissociation constant values for polySia-lipid bilayer complex, the fluorescence intensity of polySia bound to giant vesicles, the polySia-to-membrane FRET signal at the plasma membrane of live cells, and the decrease of the FRET signals after Endo-N treatment of the cells. These results suggest that polysialylation may be one of the determinants of protein association with liquid-ordered membrane lipid raft domains.

Upon fusion of multivesicular bodies (MVBs) with the plasma membrane, intraluminal vesicles (ILVs) are released into the extracellular space as exosomes. Since the lipid composition of the exosomal membrane resembles that of raft microdomains, the inward budding process involves the raft-like region of the MVB limiting membrane. Although published research suggests that cellular RNAs may be selectively sorted into exosomes, the molecular mechanisms remain elusive. In this review, we suggest that there is a continuous interaction of cellular RNAs with the outer (cytoplasmic) surface of MVBs and that the selection for incorporation of these RNAs into ILVs is based on their affinity to the raft-like region in the outer layer of the MVB membrane.

Polysialic acid (polySia) and oligosialic acid (oligoSia) chains are linear polysaccharides composed of sialic acid monomers. The majority of biological poly/oligoSia chains are bound to membranes. There is a large diversity of membrane poly/oligoSia in terms of chain length, occurrence, biological function, and the mode of membrane attachment. Poly/oligoSia can be anchored to a membrane via a phospholipid (polySia in bacteria), a glycosphingolipid (oligoSia in gangliosides), an integral membrane glycoprotein, or a glycoprotein attached to a membrane via glycosylphosphatidylinositol. In eukaryotic cells, the attachment of a poly/oligoSia chain to the membrane anchor is usually through α-2,3-glycosidic linkage to a galactose. In prokaryotic cells this attachment is proposed to occur through glycosidic linkage to the phosphate group of a phospholipid. Both long polySia chains attached to membrane proteins and short oligoSia attached to glycosphingolipids or membrane proteins are frequently found in neural membranes. In humans, poly/oligoSia is involved in development and plasticity of the brain, pathophysiology of schizophrenic brains, cancer metastasis, neuroinvasive potential of pathogenic bacterial strains, and the immune response. Biological roles of poly/oligoSia are based on its ability to modulate repulsive and attractive interactions between two molecules, and its ability to modulate membrane surface charge density, pH at the membrane surface, and membrane potentials.

Negatively-charged polysialic acid (polySia) chains are usually membrane-bound and are often expressed on the surface of neuroinvasive bacterial cells, neural cells, and tumor cells. PolySia can mediate both repulsive and attractive cis interactions between membrane components, and trans interactions between membranes. Positively-charged long-chain bases are widely present in cells, are often localized in membranes and can function as bioactive lipids. Here we use Langmuir monolayer technique, fluorescence spectroscopy and electron microscopy of lipid vesicles to study the role of a simple long-chain base, octadecylamine (ODA), in both cis and trans interactions mediated by polySia in model membranes composed of ODA and dioleoylphospatidycholine (DOPC). When added free to an aqueous solution, polySia increases the collapse pressure of ODA/DOPC monolayers, reduces the effect of ODA on the limiting molecular area, inverses the values of excess area per molecule and of excess free energy of mixing from positive to negative, and induces fusion of ODA/DOPC vesicles. These results suggest that a polySia chain can act as a multi-bridge that mediates cis interactions between different components of a lipid membrane, disrupts membrane aggregates, and mediates trans interactions between lipids in apposing membranes. These observations imply that polySia in cellular systems can act in a similar way.

Noncovalent DIDS binding to Band 3 (AE1) protein in human erythrocyte membranes, modified by non-penetrating, water soluble 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)-carbodiimide iodide (EAC), was studied at 0°C in the presence of 165 mM KCl. Under experimental conditions applied up to (48 ± 5) % of irreversible chloride self-exchange inhibition was observed. The apparent dissociation constant, KD, for “DIDS-Band 3” complex, determined from the chloride transport experiments, was (34 ± 3) nM and (80 ± 12) nM for control and EAC-treated resealed ghosts, respectively. The inhibition constant, Ki, for DIDS was (35 ± 6) nM and (60 ± 8) nM in control and EAC-treated ghosts, respectively. The reduced affinity for DIDS reversible binding was not a result of negative cooperativity of DIDS binding sites of Band 3 oligomer since Hill’s coefficients were indistinguishable from 1 (within the limit error) both for control and EAC-treated ghosts. By using tritium-labeled DIDS, 4,4’-diisothiocyanato-2,2’-stilbenedisulfonate ([3H]DIDS), the association rate constant, k+1 (M−1s−1), was measured. The mean values of (4.3 ± 0.7) × 105 M−1s−1 for control and (2.7 ± 0.7) × 105 M−1s−1 for EAC-treated ghosts were obtained. The mean values for KD, evaluated from [3H]DIDS binding measurements, were (37 ± 9) nM and (90 ± 21) nM for control and EAC-modified ghosts, respectively. The results demonstrate that EAC modification of AE1 reduces about 2-fold the affinity of AE1 for DIDS. It is suggested that half of the subunits are modified near the transport site by EAC.

Polysialic acid (polySia) is expressed on the surface of neural cells, neuroinvasive bacterial cells and several tumor cells. PolySia chains attached to NCAM can influence both trans interactions between membranes of two cells and cis interactions. Here, we report on the involvement of phospholipids in regulation of membrane interactions by polySia. The pH at the surface of liposomes, specific molecular area of phosphatidylcholine molecules, phase transition of DPPC bilayers, cyclic voltammograms of BLMs, and electron micrographs of phosphatidylcholine vesicles were studied after addition of polysialic acid free in solution. The results indicate that polySia chains can associate with phosphatidylcholine bilayers, incorporate into the polar part of a phospholipid monolayer, modulate cis interactions between phosphatidylcholine molecules, and facilitate trans interactions between apposing phospholipid vesicles. These observations imply that polySia attached to NCAM or to lipids can behave similarly.

Simple nucleotide templating activities are of interest as potential primordial reactions. Here we describe the acceleration of 5′-5′ AppA synthesis by 3′-5′ poly(U) under normal solution conditions. This reaction is apparently templated via complementary U:A base-pairing, despite the involvement of two different RNA backbones, because poly(U), unlike other polymers, significantly stimulates AppA synthesis. These interactions occur in moderate (K+) and (Mg2+) and are temperature sensitive, being more efficient at 10°C than at 4°C, but absent at 20°C. The reaction is only slightly pH sensitive, despite potentially relevant substrate pKa’s. Kinetic data explicitly support production of AppA by interaction of stacked 2MeImpA and pA nucleotides paired with a single molecule of U template. At a lower rate, AppA can also be produced by a chemical reaction between 2MeImpA and pA, without participation of poly(U). Molecular modeling suggests that 5′-5′ joining between stacked or concurrently paired A's can occur without major departures from normal U-A helical coordinates. So, coenzyme-like 5′-5′ purine dinucleotides might be readily synthesized from 3′-5′ RNAs with complementary sequences.

We have studied RNA binding to vesicles bounded by ordered and disordered phospholipid membranes. A positive correlation exists between bilayer order and RNA affinity. In particular, structure-dependent RNA binding appears for rafted (liquid-ordered) domains in sphingomyelin-cholesterol-1,2-dioleoyl-sn-glycero-3-phosphocholine vesicles. Binding to more highly ordered gel phase membranes is stronger, but much less RNA structure-dependent. All modes of RNA-membrane association seem to be electrostatic and headgroup directed. Fluorometry on 1,2-dimyristoyl-sn-glycero-3-phosphocholine liposomes indicates that bound RNA broadens the gel-fluid melting transition, and reduces lipid headgroup order, as detected via fluorometric measurement of intramembrane electric fields. RNA preference for rafted lipid was visualized and confirmed using multiple fluorophores that allow fluorescence and fluorescence resonance energy transfer microscopy on RNA molecules closely associated with ordered lipid patches within giant vesicles. Accordingly, both RNA structure and membrane order could modulate biological RNA-membrane interactions.

In the present study we investigated phospholipid bilayer membranes and phospholipid vesicles made from dioleoylphosphatidylcholine (DOPC) or its mixture with the phosphate ester derivative of long-chain polyprenol (hexadecaprenyl diphosphate, C80-PP) by electrophysiological and transmission electron microscopy (TEM) techniques. The membrane conductance-temperature relationships and the membrane breakdown voltage have been measured for different mixtures of C80-PP/DOPC. The current-voltage characteristics, the membrane conductance, the activation energy of ion migration across the membrane and the membrane breakdown voltage were determined. Hexadecaprenyl diphosphate decreases the membrane conductance, increases the activation energy and the membrane breakdown voltage for the various values of C80-PP/DOPC mole ratio. The analysis of TEM micrographs shows several characteristic structures, which have been described. The data indicate that hexadecaprenyl diphosphate modulates the surface curvature of the membranes by the formation of aggregates in liquid-crystalline phospholipid membranes. The properties of modified membranes can result from the presence of the negative charges in the hydrophilic part of C80-PP molecules and can be modulated by the concentration of this compound in membranes. We suggest that the dynamics and conformation of hexadecaprenyl diphosphate in membranes depend on the transmembrane electrical potential.

The electrochemical measurements showed that tetracosaprenol (C 120 ) isolated from leaves of Spermatophyta influenced some properties of phosphatidylcholine macrovesicular bilayer lipid membranes. The current–voltage characteristics, the membrane conductance–temperature relationships and the membrane breakdown voltage have been measured for different mixtures of tetracosaprenol and DOPC. The membrane conductance, the permeability coefficient for Cl − ions and the activation energy of ion migration across the membrane were determined. Tetracosaprenol decreases the membrane breakdown voltage and the activation energy, increases the membrane conductance and the membrane ionic permeability for Cl − ions. These results indicate that long-chain polyprenols modify bilayer lipid membranes by the formation of fluid microdomains and point to the importance of transmembrane electrical potential in the dynamics and aggregation behaviour of polyisoprenols in membranes. The results also indicate that electrical transmembrane potential can accelerate the formation of pores in lecithin–polyprenol bilayers at the microdomains border.

The application of the theory of homeomorphic transformations of topological manifolds and the operation of the connected sum of manifolds for a formation of a topological model of membrane transformations during the division process of cellular and subcellular compartments, has been shown. The biological cell and the subcellular structures in the form of vesicles are modelled by an arrangement of two concentric spheres corresponding to the inner and outer layer of the membrane bounding the vesicle. The analysis shows eight succeeding topological stages of membrane transformations during the division process and these stages are characterised. It is concluded that there is a vectorial translocation of lipid molecules from the inner layer of the membrane bounding the vesicle before the division process to the outer layer of the membranes after the division process and there is no lipid translocation from the outer layer to the inner layers during the division process.

We have shown previously that simple RNA structures bind pure phospholipid liposomes. However, binding of bona fide cellular RNAs under physiological ionic conditions is shown here for the first time. Human tRNASec contains a hydrophobic anticodon-loop modification: N6-isopentenyladenosine (i6A) adjacent to its anticodon. Using a highly specific double-probe hybridization assay, we show mature human tRNASec specifically retained in HeLa intermediate-density membranes. Further, isolated human tRNASec rebinds to liposomes from isolated HeLa membrane lipids, to a much greater extent than an unmodified tRNASec transcript. To better define this affinity, experiments with pure lipids show that liposomes forming rafts or including positively charged sphingosine, or particularly both together, exhibit increased tRNASec binding. Thus tRNASec residence on membranes is determined by several factors, such as hydrophobic modification (likely isopentenylation of tRNASec), lipid structure (particularly lipid rafts), or sphingosine at a physiological concentration in rafted membranes. From prior work, RNA structure and ionic conditions also appear important. tRNASec dissociation from HeLa liposomes implies a mean membrane residence of 7.6 min at 24°C (t½ = 5.3 min). Clearly RNA with a 5-carbon hydrophobic modification binds HeLa membranes, probably favoring raft domains containing specific lipids, for times sufficient to alter biological fates.

The study presents an application of the theory of homeomorphic transformations of topological manifolds and the operation of the connected sum of manifolds for topological analysis of membrane transformations during the fusion process between cellular and subcellular compartments. The biological cell and the subcellular structures in the form of vesicles are modelled by an arrangement of two concentric spheres corresponding to the inner and outer layer of the membrane bounding the vesicles. The analysis shows eight succeeding topological stages of membrane transformations during the fusion process and these stages are characterized. It is concluded that there is a vectorial translocation of lipid molecules from the outer layers of the membranes before the fusion process to the internal layer of the membrane bounding the vesicle after the fusion process and there is no lipid translocation in the reverse direction.

A growing number of RNA aptamers have been selected experimentally using the SELEX combinatorial approach, and these aptamers have several advantages over monoclonal protein antibodies or peptides with respect to their applications in medicine and nanobiotechnology. Relatively few successful selections have been reported for membrane molecular targets, in contrast to the situation with non-membrane molecular targets. This review compares the procedures and techniques used in selections against membrane proteins and membrane lipids. In the case of membrane proteins, the selections were performed against soluble protein fragments, detergent-membrane protein mixed micelles, whole cells, vesicles derived from cellular membranes, and enveloped viruses. Liposomes were used as an experimental system for the selection of aptamers against membrane lipids. RNA structure-dependent aptamer binding for rafts in lipid vesicles was reported. Based on the selected aptamers against DOPC and the amino acid tryptophan, a specific passive membrane transporter composed of RNA was constructed. The determination of the selectivity of aptamers appears to be a crucial step in a selection, but has rarely been fully investigated. The selections, which use whole cells or vesicles derived from membranes, can yield aptamers not only against proteins but also against membrane lipids.

Seven new arginine binding motifs have been selected from a heterogeneous RNA pool containing 17, 25, and 50mer randomized tracts, yielding 131 independently derived binding sites that are multiply isolated. The shortest 17mer random region is sufficient to build varied arginine binding sites using five different conserved motifs (motifs 1a, 1b, 1c, 2, and 4). Dissociation constants are in the fractional millimolar to millimolar range. Binding sites are amino acid side-chain specific and discriminate moderately between L- and D-stereoisomers of arginine, suggesting a molecular focus on side-chain guanidinium. An arginine coding triplet (codon/anticodon) is highly conserved within the largest family of Arg sites (72% of all sequences), as has also been found in minimal, most prevalent RNA binding sites for Ile, His, and Trp.

We have incorporated an RNA binding site for the biological amino acid tryptophan within an RNA complex with affinity for phospholipid bilayer membranes. The resulting RNA (9:10Trp) creates a selective route through the bilayer for the amino acid. Binding and enhanced tryptophan permeability are nonlinear in RNA concentration, suggesting that RNA aggregation is required for both. Tryptophan permeability saturates with increased concentration, though at ~1000-fold greater level than when binding a free aptamer. The RNA (9:10Trp) complex, bound at a mean of two per liposome, halves the activation energy for tryptophan transport (to 46 kJ/mole), specifically increasing tryptophan entry to a maximal velocity of 0.5 sec-1 per liposome with little or no accompanying increase in general permeability. Individual RNAs turn over tens of thousands of times at high tryptophan concentration. Thus, a specific passive membrane transporter whose properties overlap those of single-molecule transporter proteins, can be made of RNA alone. Permeability changes probably rely on disturbances in lipid conformation as well as on an advantageous low free energy position for tryptophan at the membrane. Other RNA activities may yield other RNA-membrane nanosystems via this route.

Polysialic acid (polySia) is a long polyanionic polymer (with the degree of polymerization, DP, up to 200) of negatively charged sialic acid monomers. PolySia chains are bound to the external surface of some neuroinvasive bacterial cells and neural cells. PolySia serves as a potent regulator of cell interactions via its unusual biophysical properties. In the present paper, the analysis, based on the Goldman-Hodgkin-Katz equation, of transmembrane potential changes resulting from transmembrane translocation of polySia is performed. The relationships between the transmembrane potential and the polySia DP (up to 200), the temperature, the cation/ anion permeability ratio, and the inner/outer concentration ratio of polySia has been plotted and discussed. The maximal membrane potential changes, up to 118 mV, were found for a permeability ratio greater than one. The increase of the polySia chain length resulted in the diminution of this effect. The temperature-dependent changes in membrane potential were less than 7 mV in the range 0-50 degrees C. The change in the concentration ratio (into its reciprocal) resulted in a mirror reflection of the membrane potential curves. The results show that the expression of polySia chains in bacterial cells can be responsible for the modulation of the transmembrane potential of the bacterial inner membrane. We suggest that the polySia chains can influence the transmembrane potential of neural cell membranes in a similar way. This analysis also describes the effect of the transmembrane translocation of negatively charged polyanionic polynucleotydes on the cell membrane potential.

The analysis of polyion transmembrane translocation was performed using membrane electrical equivalent circuit. The dependence of polyion flux across membranes on time, membrane electrical conductance, membrane electrical capacitance, degree of polymerization, water solution conductance and applied transmembrane potential is discussed. The changes in polyion flux were up to 88% after 1 ms. Both the increase of polyion chain length and the decrease of membrane conductance resulted in the diminution of this effect. Inversion of flux direction was observed as a result of external potential changes. Reversal curves, representing the values of considered parameters for zero-flux were also shown. The replacement of a polyanion by a polycation of the same chain length resulted in the same shape of the surface plot but with opposite orientation. The analysis describes the effect of transmembrane potential on the translocation rate of polyanionic polysialic acid and polynucleotides, and polycationic peptides across membranes.

The electrical measurements of phospholipid bilayers and the studies of phospholipid vesicles by using the transmission electron microscopy (TEM) showed that dotriacontaprenol (C160) isolated from leaves of Spermatophyta influences some properties of membranes. The current–voltage characteristics, the membrane conductance–temperature relationships, the membrane breakdown voltage and the membrane capacitance have been measured for different mixtures of C160/DOPC. The membrane conductance, the activation energy of ion migration across the membrane and the membrane thickness were determined. Dotriacontaprenol decreases the membrane breakdown voltage, the activation energy and the membrane capacitance, and increases the membrane conductance and the membrane hydrophobic thickness. The analysis of TEM micrographs shows several characteristic structures, which have been described. The results indicate that dotriacontaprenol increases the membrane elasticity and modulates the surface curvature of the membranes by the formation of fluid microdomains. We suggest that the long polyprenols facilitate the formation of transmembrane, ions-conductive pores.

The effect of undlecaprenyl phosphate (C55-P) on dioleoylphosphatidylcholine (DOPC) bilayer lipid membranes has been studied. The current-voltage characteristics, steady-state diffusion potentials, membrane conductance-temperature relationships, membrane electric capacitance and membrane breakdown voltage have been measured for different mixtures of undecaprenyl phosphate and DOPC. The ratio of permeability coefficients for sodium and chloride ions, the activation energy for ion migration across the membrane and membrane thickness have been determined. The electrical measurements showed that undecaprenyl phosphate decreases membrane-normalized conductance, membrane ionic permeability, membrane hydrophobic thickness and membrane selectivity for chloride ions, and increases the activation energy for ion transport, membrane nonlinearity potential, membrane specific capacitance, membrane electromechanical stability and membrane selectivity for sodium ions. From the results, we suggest that the interaction of the gradient of electric transmembrane potential with the negative charge of the phosphate group of C55-P determines the dynamics, conformation and aggregation behaviour of undecaprenyl phosphate in phospholipid membranes. Some implications of these findings for a possible regulation of the C55-P-dependent expression of polysialic acid capsule in Escherichia coli K1 bacterial cells are indicated.