Figure 1.
Initial steps in the biosynthesis of lipid A-Ara4N. The pathway starts with UDP-glucose that is oxidized to UDP-glucuronic acid (UDP-GlcA) by UDP-glucose dehydrogenase (Ugd). UDP-GlcA is then oxidatively decarboxylated to UDP-4-ketopentose (UDP-Ara4O) by the C-terminal domain of ArnA. UDP-Ara4O is transaminated by ArnB to form UDP-Ara4N that, after transient formylation, sugar transfer to undecaprenyl-phosphate, and flipping to the periplasmic side of the inner membrane is finally transferred to lipid A.