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

摘要

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 coli was expressed in a recom- binant E coli strain and was shown to direct the synthesis of a soluble, 17-kDa polypeptide. The recombinant protein was found to convert 4-diphosphocytidyl-2C-methyl-D-e 2-phosphate into 2C-methyl-D-erythritol Z,4-cyclodiphosphate and CMP. The structure of the reaction product was established by NMR spec- troscopy using 13C-labeled substrate samples. The enzyme-cata- lyzed reaction requires Mn2+ or Mg2+ but no other cofactors. Radioactivity from [2-14C]2C-methyl-D-erythritol 2,4-cyclodiphos- phate was diverted efficiently to carotenoids by isolated chromo- plasts from Capsicum annuum and, thus, was established as an intermediate in the deoxyxylulose phosphate pathway of isopre- noid biosynthesis. YgbB protein also was found to convert 4-diphosphocytidyl-2C-methyl-D-erythritol into 2C-methyl-D-eryth- ritol 3,4-cyclophosphate. This compound does not serve as sub- strate for the formation of carotenoids by isolated chromoplasts and is assumed to be an in vitro product without metabolic relevance.