Critical micelle concentrations of lipoteichoic acids

Abstract

Purified lipoteichoic acids (LTAs) from several gram-positive organisms have been shown, by methods involving spectral changes of an added merocyanine dye probe, to have critical micelie concentrations in the range of 1 to 10 jig/ml, suggesting that acylated LTAs in their monomer forms may represent the major configuration of extracellular LTAs in bacterial culture fluids. The critical micelle concentrations obtained did not differ markedly with degree of carbohydrate substitution of the polymers. The significance of these findings in relation to the biological properties of LTA is discussed.Lipoteichoic acid (LTA) is the generic name given to a group of structurally related amphipathic molecules or amphiphiles found as cell membrane components in a wide range of gram-positive bacteria. The hydrophilic portion of the molecule is typically a 1,3-phosphodiester-linked polymer of glycerophosphate, variously substituted in the C-2 position of the glycerol residues with sugars in glycosidic linkage and D-alanine in ester linkage. The hydrophobic region of the molecule, linked covalently through the phosphomonoester end of the polymer, is generally either a glycolipid or phosphatidylglycolipid. This lipid "end" is intercalated with the upper half of the bilayer of the cell membrane and provides a membrane anchor for the molecule. LTA is also found as a soluble excreted product in cultures of gram-positive bacteria (29, 35).In aqueous solution, amphipathic molecules or amphiphiles tend to form micellar aggregates to occlude water from the hydrophobic regions of their molecular structure. LTAs similarly form high-molecular-weight aggregates or presumptive micelles in aqueous solution, as judged by their behavior on gel chromatography (9,29,35). Treatment with detergents reduces the high-molecular-weight aggregates to what is presumed to be a monomeric form (9). In any solution of an amphiphile, the micellar form must coexist with monomer. environment (10,25,26). Merocyanine dyes are among the more thoroughly characterized of the various types of compounds used as indicators of solvent polarities. With change in solvent polarities, their electronic spectra can show very large shifts in their absorption bands or intensity of fluorescence which in turn are presumed to be due to changes in the balance of benzenoid and quinonoid valence structure of the probe (4). The merocyanine dye most commonly used in such studies is 4-[2-(1-methyl-1,4,dihydropyridin-4-ylidene)ethylidene] cyclohexa-2-5-dien-1-one, which shows a shift in the UV-visible absorption spectrum towards longer wavelength as the solvent polarity decreases (5). More recently, an amphipathic merocyanine dye has been synthesized in which the methyl group has been replaced by a hexadecyl chain (8), thereby increasing its hydrophobic character and favoring its solubilization by micelles. Studies with this probe showed upward wavelength shifts in its absorption spectrum in solutions of various detergents as the concentrations of the latter were increased from below to ...

Effect of lipoteichoic acid on the uptake of Streptococcus pyogenes by HEp-2 cells

“…A possible explanation for such a phenomenon is that LTA micelles exert a cytotoxic e¡ect upon epithelial cells. The critical micelle concentration (CMC) of LTA, from several bacterial species, ranges from 1 to 10 Wg ml 31 [28] or 28 to 60 Wg ml 31 [29]. LTA at concentrations higher than CMC induced the lysis of sheep erythrocytes and was cytotoxic for Girardi heart cells, suggesting that micellar LTA may cause disruption of the erythrocyte membrane and may be cytotoxic for cells in culture [28].…”

A Continuum of Anionic Charge: Structures and Functions ofd-Alanyl-Teichoic Acids in Gram-Positive Bacteria

“…In Staphylococcus epidermidis, the solid component of the slime layer is approximately 80% (wt/wt) TA and 20% protein (234). Based on immunochemical labeling studies and LTA turnover experiments, Wicken et al (497,501) concluded that LTA would be expected to be a component of the glycocalyx and thus to play an important role in its function. It was proposed that the spatial divisions of the wall and glycocalyx are not rigid but "represent regions in a continuum and individual types of cell-wall-associated polymers may be distributed across the continuum both spatially and also temporally if they are in transit" (501).…”

Bifidobacterial Lipoglycan as a New Cause for False-Positive Platelia Aspergillus Enzyme-Linked Immunosorbent Assay Reactivity

“…Secretion is stimulated by exposure to ␤-lactam antibiotics (9,12,33,35). In aqueous solutions, the acylated molecules form micellar aggregates (53).…”