Biosynthesis of the tunicamycins: a review.

Tunicamycins are nucleotide sugar analogs produced by several Streptomyces species. In eukaryotes, tunicamycins inhibit UDP-N-acetylglucosamine: dolichol phosphate GlcNAc-1-P transferase (GPT) that catalyzes the first step in protein glycosylation. In bacteria they inhibit UDP-N-acetylmuramoyl-pentapeptide: undecaprenol phosphate MurNAc-pentapeptide-1-P transtransferase (MraY) that catalyzes an early stage in peptidoglycan cell wall assembly. Tunicamycins are substrate analog of GPT and MraY, such that the alphabeta-1'',11'-linked GlcNAc residue of the tunicamycins mimics the transferred GlcNAc-1-phosphate. The unusual structure of tunicamycins, particularly the unique 11-carbon sugar, tunicamine, and the alphabeta-1'',11'-O-glycosidic linkage, suggest its biosynthesis to be unique. This review discusses potential biosyntheses for tunicamycins via the synthesis and conjugation of uridine-5'-aldehyde and UDP-4-keto-N-acetylgalactosamine-5,6-ene and the subsequent formation of the alpha,beta-1'',11' glycosidic linkage.