Effect of lipoteichoic acid on thermotropic membrane properties

Abstract

Lipoteichoic acid, diglucosyldiacylglycerol, and phosphatidylglycerol isolated from Staphylococcus aureus were embedded in dipalmitoylglycerophosphoglycerol vesicles, and their thermotropic influence on this matrix was studied by differential scanning calorimetry. The natural fatty acids of phosphatidylglycerol effected peak broadening and a decrease in molar heat capacity. These effects were more pronounced with the glycolipid, which also increased the main transition temperature. With the lipoteichoic acid mixtures, two broad main transition peaks were observed, possibly due to different levels of lipoteichoic acid in vesicles. Both peaks showed a further upshift in transition temperatures and a pronounced decrease in molar heat capacity. Since the diacylglycerol moieties of all three amphiphiles were practically identical, the differences in the thermotropic effects have to be ascribed to the different structures of the head groups. Diglucosyldiacylglycerol is proposed to exert an additional effect by hydrogen bonding the hydroxyls of the sugar rings to their phospholipid neighbors. The stronger effect of lipoteichoic acid points to dynamic interactions of the long hydrophilic chain with the vesicle surface, which stabilize the membrane structure.Characteristic lipid components of the cytoplasmic membrane of many gram-positive bacteria are glycolipids and lipoteichoic acids (LTAs) (7). For example, the cytoplasmic membrane of Staphylococcus aureus contains LTA, diglucosyldiacylglycerol (DGDG), phosphatidylglycerol (PG), diacylglycerol, and lysylphosphatidylglycerol, which are present during exponential growth at 6, 8, 50, 24, and 10 mol%, respectively. Trace amounts of monoglucosyldiacylglycerol are also present, and toward the end of exponential growth, variable amounts of bisphosphatidylglycerol (cardiolipin) are formed (16). LTA is biosynthetically derived from DGDG, on which a linear chain of an average of 25 1,3-linked glycerophosphate residues is polymerized by the transfer of glycerophosphate from PG. Owing to the long hydrophilic chain, LTA contains more than 50% of the total membrane lipid glycerol. The concentration of LTA in the outer membrane layer is 12 mol%, which means that each LTA molecule is surrounded by eight lipid molecules.Although LTA was discovered 25 years ago and has been considered an essential cellular component, little is known about its physiological functions (2, 7). Several biological activities associated with the hydrophilic chain were described, but the structural diversity of the hydrophilic chain with regard to D-alanine ester content, substitution with glycosyl residues, and in particular net electric charge rendered a general function based on the chain structure unlikely. We therefore focused on LTA's role as a membrane constituent and searched for its influence on the physicochemical properties of the membrane.Recent X-ray scattering analysis revealed that LTAs are unique because they form micellar supramolecular structures in aqueous dispersion (18), in contrast to me...

Staphylococcus aureuslipoteichoic acid triggers inflammation in the lactating bovine mammary gland

“…1). Assuming that LTA makes up about 2% of the dry cell weight [19], 20 g LTA would equate to several billion staphylocci, numbers well above the numbers found in mastitic udders. Nevertheless, LTA is likely to be of biological significance because (i) recent data indicate that the physical presentation of LTA (such as immobilization on a solid surface) increases LTA activity by several orders of magnitude [11]; and (ii) LTA can act synergistically with other PAMP, which could still lower the amount required to induce inflammation by an order of magnitude.…”

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

“…Micelles with a decreased LTA concentration do not trap or sequester autolysins, and therefore the inhibitory action of LTA that had originally been described with high-density micelles may have led to an equivocal conclusion. A molecule of membraneassociated LTA in the cell is surrounded, on average, by eight phospholipid molecules (195). Under these conditions, LTA binds autolysin for presentation to the susceptible peptidoglycan linkages.…”

“…18) with a type I LTA in the absence of other wall components, e.g., peptidoglycan. In a biophysical analysis of type I LTA, Gutberlet et al (195) observed two types of interaction that occur with LTA in vesicles of dipalmitoyl-sn-glycero-3-phospho-1-glycerol (DPPG) at high ionic strength. The first occurs between the glucosyl hydroxyl groups of the LTA glycolipid anchor and the phosphoglycerol moiety of adjacent DPPG.…”

Autolysis of Lactococcus lactis Is Increased upon d -Alanine Depletion of Peptidoglycan and Lipoteichoic Acids

“…Lipoteichoic acid (LTA) is a candidate-hindering component that is removed by this treatment, as it seems to be present in L. lactis at those positions where AcmA is not able to bind (49). LTA is a secondary cell wall polymer suggested to be involved in the control of autolysin activity (5,15), in determining the electrochemical properties of the cell wall (42), in establishing a magnesium ion concentration (2, 21, 26, 31), and in determining the physicochemical properties of the cytoplasmic membrane (18). LTA can be modified by various compounds, such as glycosyl residues (15) and D-Ala esters (1).…”