Biosynthesis of terpenoids: YgbB protein converts 4-diphosphocytidyl-2C-methyl-D-erythritol 2-phosphate to 2C-methyl-D-erythritol 2,4-cyclodiphosphate

In many microorganisms, the putative orthologs of the Escherichia coli ygbB gene are tightly linked or fused to putative orthologs of ygbP, which has been shown earlier to be involved in terpenoid biosynthesis, The ygbB gene of E. coil was expressed in a recombinant E. coil strain and was shown to d irect the synthesis of a soluble, 17-kDa polypeptide. The recombinant prote in was found to convert 4-diphosphocytidyl-2C-methyl-D-erythrito 2-phosphat e into 2C-methyl-D-erythritol 2,4-cyclodiphosphate and CMP, The structure o f the reaction product was established by NMR spectroscopy using C-13-label ed substrate samples. The enzyme-catalyzed reaction requires Mn2+ or Mg2+ b ut no other cofactors, Radioactivity from [2-C-14]2C-methyl-D-erythritol 2, 4-cyclodiphosphate was diverted efficiently to carotenoids by isolated chro moplasts from Capsicum annuum and, thus, was established as an intermediate in the deoxyxylulose phosphate pathway of isoprenoid biosynthesis. YgbB pr otein also was found to convert 4-diphosphocytidyl-2C-methyl-D-erythrito in to 2C-methyl-D-erythritol 3,4-cyclophosphate. This compound does not serve as substrate for the formation of carotenoids by isolated chromoplasts and is assumed to be an in vitro product without metabolic relevance.