Fig. 5

Model depicting the effect of increasing Und-P on glycan expression. (A) Und-P synthesis. Und-P is synthesized via the methylerythritol phosphate (MEP) pathway. Und-P is first synthesized as Und-PP by the UppS synthase. Integral membrane phosphatases (BacA/PAP2 family proteins) then dephosphorylate Und-PP to Und-P (the level of which is visually indicated by the black wavy line in the bucket icon). Und-P is then distributed to phosphoglycosyl transferases and glycosyltransferases (PGT/GTs) that prime glycan assembly in non-essential and essential (peptidoglycan) pathways. In E. coli K-strains, PGT/GTs transfer precursors of peptidoglycan (MraY), O-antigen (WecA), enterobacterial common antigen (WecA), and colanic acid (WcaJ) to Und-P. Und-P is also required to glycosylate lipid A with aminoarabinose (ArnC) and O-antigen with glucose (GtrB). Since Und-P limits glycan assembly (gear icon), the glycosylation potential of any bacterium is limited by Und-P availability. (B) Simultaneously deleting all non-essential PGT/GTs and overexpressing uppS increases the amount of Und-P available for recombinant glycan expression. Our findings indicate that increasing Und-P levels increases both glycan yield and chain length