Chain-length determination mechanism of isoprenyl diphosphate synthases and implications for molecular evolution

In the synthesis of isoprenoids, isoprenyl diphosphate synthases catalyze the consecutive condensation of isopentenyl diphosphate with allylic diphosphates to produce a variety of prenyl diphosphates with well-defined chain lengths. Site-directed mutagenesis in conjunction with X-ray crystallographic studies have identified specific amino acid residues responsible for:chain-length determination. Simple combinations of these residues within a characteristic motif are not only sufficient to confer product specificities: to all isoprenyl diphosphate synthases but represent. structural features that reflect the enzyme family's evolutionary course.