Fig. 2.

Enzymes required for glycolipid and LTA backbone synthesis in different Gram-positive bacteria. Schematic representation of enzymes involved in glycolipid precursor, glycolipid and/or LTA backbone synthesis in (a) Staphylococcus aureus, (b) Bacillus subtilis, (c) Listeria monocytogenes, (d) Streptococcus pneumoniae, (e) Streptococcus agalactiae and (f) Enterococcus faecalis. Enzymes with experimental evidence for their activity are shown in color and their function is described in the text, while enzymes identified by blast searches based on homology are shown in gray. Predicted but still unidentified proteins are indicated with question marks (?). Glycolipid synthesis precursors are UDP nucleotide-activated sugars that are produced in the cytoplasm of the cell. These precursors are used by glycosyltransferases to synthesize the LTA glycolipid anchor by the transfer of glucose (red circles) or galactose (green circle) moieties onto the membrane lipid DAG. After transport of the glycolipid from the inside to the outside of the membrane, GroP subunits (yellow circles) derived from the membrane lipid phosphatidylglycerol are added to the anchor and the chain is extended by the repeated addition of GroP subunits at the distal end. This leads to the formation of the PGP-LTA backbone chain, which is schematically depicted by a string of yellow circles. In contrast, the non-PGP-type LTA in S. pneumoniae (d) is depicted by different symbols. Proteins are either named according to the information available in the literature or based on L. monocytogenes EGD-e, S. pneumoniae R6, S. agalactiae NEM316, and E. faecalis V583 gene numbers. Abbreviations used are as follows: Glc-6-P, glucose-6-phosphate; Glc-1-P, glucose-1-phosphate; Glc₂-DAG, diglucosyldiacylglcerol; GalGlc-DAG, galactosylglucosyldiacylglycerol.