Terpene biosynthesis enzymes prenyltransferases

Prenylation, the key step in terpene biosynthesis, is catalyzed by prenyltransferases. These enzymes are responsible for the condensation of isopentenyl pyrophosphate (IPP) with an allyl pyrophosphate, thus yielding isoprenoids. Numerous studies have been performed with fluorinated substrates in order to determine the mechanism of the reactions that involve these enzymes prenyltransferases, farnesyl diphosphate synthase (FDPSase), famesyltransferase (PFTase), and IPP isomerase. These studies are based on the potential ability of fluorine atoms to destabilize cationic intermediates, and then slow down S l type processes in these reactions. 

As presented in this chapter, today, much is known about the process of terpene biosynthesis. The accumulated knowledge includes a detailed picture about the biosynthesis of the terpenoid monomers IPP and DMAPP either via the mevalonate or the DXP route and their interconversion by isomerases. Also, the stereochemical courses and enzyme mechanisms of all transformations have been largely elucidated. Especially the recently obtained structural data of prenyltransferases and various kinds of terpene synthases resulted in an evolutionary model that involves six domains (a, P, 7,8, e, and Q for the biosynthesis of linear polyisoprenoids from IPP and DMAPP and their subsequent transformation into (poly)cyclic terpenes. All these insights may open up new chances in controlling terpene biosynthesis, e.g., by directed evolution of terpene cyclases or domain swaps in multi-domain enzymes for the production of new terpenes, reconstitution of terpene biosynthetic pathways in heterologous hosts for production optimization, or targeted inhibitirm of pathways in pathogens for disease control. 

Other enzymes involved in terpene biosynthesis have also been harnessed for biocatalytic reactions of arenes. Prenyltransferase enzymes that can affect the addition of Cj isoprenyl units both at carbon and at heteroatoms have been used for biocatalytic arene alkylations. For example, L-tryptophan 49 undergoes prenylation at various positions on the indole core in a wholly regiose-lective fashion, depending on the enzyme used [28] (Scheme 32.6). 

Microbial cell factories [194] have recently been developed for the production of terpenoids such as sclareol [195], and, as was shown in the previous section, valencene and nootkatone. The genes responsible for the biosynthesis of the desired compound, such as prenyltransferases, terpene synthases, and additional transformation enzymes, are selected from a natural source and transferred into a host, usually S. cerevisiae or . coli, suitably engineered to overproduce IPP and DMAPP. High productivity values for a commercially exploitable production are achieved by further metabolic and bioprocess engineering improvements of the microbial system. 

---