The structure of pneumococcal lipoteichoic acid

Abstract

Pneumococcal lipoteichoic acid was extracted and purified by a novel, quick and effective procedure. Structural analysis included methylation, periodate oxidation, Smith degradation, oxidation with CrO₃, and fast-atom-bombardment mass spectrometry. Hydrolysis with 48% (by mass) HF and subsequent phase partition yielded the lipid anchor (I), the dephosphorylated repeating unit of the chain (II) and a cleavage product of the latter (III). The proposed structures are: where AATGal is 2-acetamido-4-amino-2,4,6-trideoxygalactose, and all sugars are in the pyranose form and belong to the d-series. Alkaline phosphodiester cleavage of lipoteichoic acid, followed by treatment with phosphomonoesterase, resulted in the formation of II and IV, with IV as the prevailing species: The linkage between the repeating units was established as phosphodiester bond between ribitol 5-phosphate and position 6 of the glucosyl residue of adjacent units. The chain was shown to be linked to the lipid anchor by a phosphodiester between its ribitol 5-phosphate terminus and position 6 of the non-reducing glucosyl terminus of I. The lipoteichoic acid is polydisperse: the chain length may vary between 2 and 8 repeating units and variations were also observed for the fatty acid composition of the diacylglycerol moiety. Preliminary results suggest that repeating units II and IV are enriched in separate molecular species. All species were associated with Forssman antigenicity, albeit to a various extent when related to the non-phosphocholine phosphorus. Owing to its unique structure, the described macroamphiphile may be classified as atypical lipoteichoic acid.