Voltage-dependent behaviour of dolichyl phosphate-phosphatidylcholine bilayer lipid membranes

Membrane potential-dependent binding of polysialic acid to lipid monolayers and bilayers

Polysialic acids are linear polysaccharides composed of sialic acid monomers. These polyanionic chains are usually membrane-bound, and are expressed on the surfaces of neural, tumor and neuroinvasive bacterial cells. We used toluidine blue spectroscopy, the Langmuir monolayer technique and fluorescence spectroscopy to study the effects of membrane surface potential and transmembrane potential on the binding of polysialic acids to lipid bilayers and monolayers. Polysialic acid free in solution was added to the bathing solution to assess the metachromatic shift in the absorption spectra of toluidine blue, the temperature dependence of the fluorescence anisotropy of DPH in liposomes, the limiting molecular area in lipid monolayers, and the fluorescence spectroscopy of oxonol V in liposomes. Our results show that both a positive surface potential and a positive transmembrane potential inside the vesicles can facilitate the binding of polysialic acid chains to model lipid membranes. These observations suggest that these membrane potentials can also affect the polysialic acid-mediated interaction between cells.

Modulation of properties of phospholipid membranes by the long-chain polyprenol (C(160))

The electrical measurements of phospholipid bilayers and the studies of phospholipid vesicles by using the transmission electron microscopy (TEM) showed that dotriacontaprenol (C(160)) 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 C(160)/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 hexadecaprenyl diphosphate on phospholipid membranes

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, C(80)-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 C(80)-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 C(80)-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 C(80)-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.

Interaction of undecaprenyl phosphate with phospholipid bilayers

The effect of undecaprenyl 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.