CONVERSION FROM ARCHAEAL GERANYLGERANYL DIPHOSPHATE SYNTHASE TO FARNESYL DIPHOSPHATE SYNTHASE - 2 AMINO-ACIDS BEFORE THE FIRST ASPARTATE-RICH MOTIF SOLELY DETERMINE EUKARYOTIC FARNESYL DIPHOSPHATE SYNTHASE ACTIVITY

Farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP) are p recursors for a variety of important natural products, such as sterols , carotenoids, and prenyl quinones, Although FPP synthase and GGPP syn thase catalyze similar consecutive condensations of isopentenyl diphos phate with allylic diphosphates and have several homologous regions in their amino acid sequences, nothing is known about how these enzymes form the specific products. To locate the region that causes the diffe rence of final products between GGPP synthase and FPP synthase, we con structed six mutated archaeal GGPP synthases whose regions around the first aspartate-rich motif were replaced with the corresponding region s of FPP synthases from human, rat, Arabidopsis thaliana, Saccharomyce s cerevisiae, Escherichia coli, Bacillus stearothermophilus, and from some other related mutated enzymes. From the analysis of these mutated enzymes, we revealed that the region around the first aspartate-rich motif is essential for the product specificity of all FPP synthases an d that the mechanism of the chain termination in eukaryotic FPP syntha ses (type I) is different from those of prokaryotic FPP synthases (typ e II). In FPP synthases of type I, two amino acids situated at the fou rth and the fifth positions before the motif solely determine their pr oduct chain length, while the product specificity of the type II enzym es is determined by one aromatic amino acid at the fifth position befo re the motif, two amino acids inserted in the motif, and other modific ations, These data indicate that FPP synthases have evolved from the p rogenitor corresponding to the archaeal GGPP synthase in two ways.