Fig. 6
From: Lipoteichoic acid deficiency permits normal growth but impairs virulence of Streptococcus pneumoniae
Last steps in the TA biosynthesis pathway in S. pneumoniae. The Und-PP-linked monomeric repeats are polymerized by the RU polymerase and transported through the cytosolic membrane by TacF. The complete biosynthesis pathway is reviewed and discussed in ref. 15. Finally, the pnTA precursor chain is transferred onto the PGN to form the pnWTA or onto the glycolipid anchor to form the pnLTA, respectively. The transfer to the PGN is performed—most likely in a semi-redundant manner19—by the LCP proteins Psr, LytR, and Cps2A. Here the TA chain is transferred including one phosphate, thus retaining the anomeric α-configuration of the AATGalp moiety of the first RU. In pnLTA formation, a new glycosidic bond between the glucose moiety of the glycolipid anchor and the first AATGalp is formed. We propose that TacL may catalyze this reaction, which inverts the stereochemistry of the anomeric carbon leading to the β-configuration of the AATGalp moiety of the first RU in pnLTA. From these observations, it can be concluded that the Und-PP-linked pnTA precursor chains are synthesized with all AATGalp moieties in the α-configuration. AATGal 2-acetamido-4-amino-2,4,6-trideoxygalactose, CM cytoplasmic membrane, GalNAc N-acetylgalactosamine, Glc glucose, LCP LytR-Cps2A-Psr family protein
