Undecaprenyl diphosphate synthase (UPS) catalyzes the cis-prenyl chain elongation onto trans, trans-farnesyl diphosphate (FPP) to produce undecaprenyl diphosphate (UPP), which is indispensable for the biosynthesis of bacterial cell walls. We report here the crystal structure of UPS as the only three-dimensional structure among cis-prenyl chain elongating enzymes. The structure is classified into a protein fold family and is completely different from the so-called ''isoprenoid synthase fold'' that is believed to be a common structure for the enzymes relating to isoprenoid biosynthesis. Conserved amino acid residues among cis-prenyl chain elongating enzymes are located around a large hydrophobic cleft in the UPS structure. A structural P-loop motif, which frequently appears in the various kinds of phosphate binding site, is found at the entrance of this cleft. The catalytic site is determined on the basis of these structural features, from which a possible reaction mechanism is proposed.

Orotidine-5'-monophosphate decarboxylase (ODCase) has evolved to catalyze a decarboxylation reaction, most probably via a carbanion species at the C6 position of orotidine-5'-monophosphate. We reveal an unusual biochemical pathway of conversion of 6-cyano-uridine-5'-monophosphate by ODCase to barbiturate-5'-monophosphate via perhaps an electrophilic center at the C6 position, leading to inhibition. This potential of ODCase is very useful in the design of novel inhibitors.