4-Diphosphocytidyl-2-C-methylerythritol (or CDP-ME) is an intermediate in the MEP pathway (non-mevalonate pathway) of isoprenoid precursor biosynthesis. It is produced by the enzyme 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase (IspD) and is a substrate for CDP-ME kinase (IspE).
Biochemical role
CDP-ME is an intermediate in the non-mevalonate pathway for the biosynthesis of the isoprenoid precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate. Most gram-negative bacteria, the photosynthetic cyanobacteria and green algae use only this pathway, while higher plants also use the mevalonate pathway.
The enzyme 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase combines 2-C-methylerythritol 4-phosphate and cytidine triphosphate to form CDP-ME, with a pyrophosphate (PPi) fragment as a byproduct:
In the next step, the enzyme 4-(cytidine 5'-diphospho)-2-C-methyl-D-erythritol kinase uses the cofactor, adenosine triphosphate (ATP) to introduce a terminal phosphate group, giving 4-diphosphocytidyl-2-C-methyl-D-erythritol 2-phosphate (CDP-MEP) and adenosine diphosphate (ADP):
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