Schematic illustration of the peptidoglycan synthesis pathway in E. coli, highlighting the central role of the undecaprenyl pyrophosphate (C55-PP) phosphatase enzymes (purple). The cytosolic precursor, uridine diphosphateN-acetylmuramyl-pentapeptide (UM5), reacts with C55-P to form lipid I through the action of MraY and is then glycosylated by MurG to form lipid II. Following lipid II flipping into the periplasm, where the glycopeptide moiety is incorporated into the nascent peptidoglycan, the carrier lipid is released in the form of a diphosphate (C55-PP). C55-PP is then dephosphorylated by UppP or the PAP2-type phosphatases (PgpB, LpxT, and YbjG) and then flipped such that the phosphate head faces the cytosol to re-enter the pathway.
