Abstract
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.
Highlights
The superposition of the transmembrane potential, the dipole potentials, and the difference in the surface potentials gives rise to the potential inside the membrane [1]
We use the metachromatic shift in the maximum absorption of toluidine blue, the Langmuir monolayer technique, fluorescence anisotropy of DPH, and transmembrane potential-dependent fluorescence of oxonol V in lipid vesicles to study the effects of experimentally generated membrane surface potential and transmembrane potential on the binding of polysialic acid to model lipid membranes
The effect of the surface potential on Polysialic acid (polySia) binding to the lipid bilayer and monolayer To study the effect of the surface potential of liposomal membranes on the binding of polysialic acid to liposomes, we mixed polySia with DOPC liposomes modified by positively charged ODA at an ODA/DOPC molar ratio of 0.05
Summary
The superposition of the transmembrane potential, the dipole potentials, and the difference in the surface potentials gives rise to the potential inside the membrane (intramembrane potential) [1]. The dipole potential is generated inside the membrane by the intramolecular dipole moments of lipids, proteins and water molecules, e.g. by the ester linkage of the hydrocarbon chains of phospholipids. Polysialic acid (polySia) chains are linear polysaccharides composed of sialic acid monomers They are usually anchored to a membrane via a phospholipid, an integral membrane glycoprotein or a glycoprotein attached to the membrane via glycosylphosphatidylinositol. PolySia chains have a high degree of hydration, and the hydrated volume can regulate the distance between membranes and receptor– receptor interaction [20] Both experimental and theoretical studies indicate that polyanionic polySia at the membrane surface can increase the absolute value of negative surface potential, decrease pH at the membrane surface, and modulate the value of negative transmembrane potential [22,23]. We use the metachromatic shift in the maximum absorption of toluidine blue, the Langmuir monolayer technique, fluorescence anisotropy of DPH, and transmembrane potential-dependent fluorescence of oxonol V in lipid vesicles to study the effects of experimentally generated membrane surface potential and transmembrane potential on the binding of polysialic acid to model lipid membranes
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