Expanding the Isoprenoid Building Block Repertoire with an IPP Methyltransferase from Streptomyces monomycini

Many synthetic biology approaches aim at expanding the product diversity of enzymes or whole biosynthetic pathways. However, the chemical structure space of natural product forming routes is often restricted by the limited cellular availability of different starting intermediates. Although the terpene biosynthesis pathways are highly modular, their starting intermediates are almost exclusively the C-5 units IPP and DMAPP. To amplify the possibilities of terpene biosynthesis through the modification of its building blocks, we identified and characterized a SAM-dependent methyltransferase converting IPP into a variety of C-6 and C-7 prenyl pyrophosphates. Heterologous expression in Escherichia tali not only extended the intracellular prenyl pyrophosphate spectrum with mono- or dimethylated IPP and DMAPP, but also enabled the biosynthesis of C-11, C-12,C- C-16, and C-17 prenyl pyrophosphates. We furthermore demonstrated the general high promiscuity of terpenoid biosynthesis pathways toward uncommon building blocks by the E. tali-based production of polymethylated C-41, C-42, and C-43 carotenoids. Integration of the IPP methyltransferase in terpene synthesis pathways enables an expansion of the terpenoid structure space beyond the borders predetermined by the isoprene rule which indicates a restricted synthesis by condensation of C-5 units.