Structural feature of the major but not cytokine-inducing molecular species of lipoteichoic acid.

Previously, lipoteichoic acid (LTA) of Enterococcus hirae was found to exhibit definite cytokine-inducing activity but synthetic specimens which share the fundamental structural principles proposed for LTA had no corresponding activity. We also showed recently that several minor components totally less than 5% of the LTA fraction from E. hirae ATCC 9790 possessed the activity, whereas the major component (over 90%) did not [Suda, Y., Tochio, H., Kawano, K., Takada, H., Yoshida, T., Kotani, S., and Kusumoto, S. (1995) FEMS Immun. Med. Microbiol. 12, 97-112]. In the present study, the structure of the major component of LTA was studied in an attempt to elucidate the reason for the lack of the activity in the synthetic compounds. The major component of the LTA was first digested by hydrofluoric acid hydrolysis to cleave phosphodiester linkages present. The hydrolysis products were separated and characterized by means of NMR and MS. The linkage positions of the original phosphodiesters were determined from the NMR spectra of an alkali-treated product without hydrofluoric acid degradation. The compound was proved to consist of 1,3-linked poly(glycerophosphate) and a lipid anchor, Glc(alpha1-2)Glc(alpha1-3)acyl(2)Gro, the former being linked to the 6-position of the distal glucose of the latter. The 2-position of the glycerol residues in the glycerophosphate part were substituted by oligoglucose esterified partially with alanine. The gross structure elucidated here thus coincides with the previous conclusion described by Fischer [Fischer, W. (1990) in Glycolipids, Phosphoglycolipids and Sulfoglycolipids (Kates, M., ed.) pp. 123 234, Plenum Press, New York]. Thus, the molecular species with this so-called "LTA structure" is not responsible for the cytokine-inducing activity.