Effect of alanine ester substitution and other structural features of lipoteichoic acids on their inhibitory activity against autolysins of Staphylococcus aureus

Abstract

Native substitution with the D-alanine ester of lipoteichoic acids (LTAs) affects their immunological properties, the capacity to bind divalent cations, and LTA carrier activity. In this study we tested the influence of the D-alanine ester on anti-autolytic activity, using extracellular autolysin from Staphylococcus aureus and nine LTAs with alanine/phosphorus molar ratios of between 0.23 and 0.71. The inhibitory activity, highest with alanine-free LTA, exponentially decreased with increasing alanine content, approaching zero at substitutions of greater than 0.6. Correspondingly, dipolar ionic phospholipids were not inhibitory, in contrast to negatively charged ones. Glycosylation of LTA up to an extent of 0.5 did not depress inhibitory activity, and even at a degree of 0.8 the effect was comparatively small. On comparison of LTAs from various sources, differences in lipid structures and chain lengths were without effect. The inhibitory activity drastically decreased when the glycolipid carried a single glycerophosphate residue or the hydrophilic chain had the unusual structure [6 leads to Gal(alpha 1--6)Gal(alpha 1--3)Gro-(2 comes from 1 alpha Gal)-P]n, in which digalactosyl moieties connect the alpha-galactosylated glycerophosphate units. Principally, the same results were obtained with the more complex system of autolysis of S. aureus cells. We hypothesize that the anti-autolytic activity of LTA resides in a sequence of glycerophosphate units and that the negative charges of appropriately spaced phosphodiester groups play a crucial role. The alanine ester effect is discussed with respect to the putative in vivo regulation of autolysins by LTA.