The Biosynthetic Gene Cluster for Sestermobaraenes-Discovery of a Geranylfarnesyl Diphosphate Synthase and a Multiproduct Sesterterpene Synthase from Streptomyces mobaraensis.

A biosynthetic gene cluster from Streptomyces mobaraensis encoding the first cases of a bacterial geranylfarnesyl diphosphate synthase and a type I sesterterpene synthase was identified. The structures of seven sesterterpenes produced by these enzymes were elucidated, including their absolute configurations. The enzyme mechanism of the sesterterpene synthase was investigated by extensive isotope labeling experiments.

Cyclization of all-E- and 2Z-geranylfarnesols by a bacterial triterpene synthase: insight into sesterterpene biosynthesis in Aleuritopteris ferns.

Aleuritopteris ferns produce triterpenes and sesterterpenes with tricyclic cheilanthane and tetracyclic 18-episcalarane skeletons. The structural and mechanistic similarities between both classes of fern terpene suggest that their biosynthetic enzymes may be closely related. We investigate here whether a triterpene synthase is capable of recognizing geranylfarnesols as a substrate, and is able to convert them to cyclic sesterterpenes. We found that a bacterial triterpene synthase converted all-E-geranylfarnesol (1b) into three scalarane sesterterpenes with 18αH stereochemistry (5, 7 and 8), as well as mono- and tricyclic sesterterpenes (6 and 9). In addition, 2Z-geranylfarnesol (4) was converted into an 18-episcalarane derivative (10), whose skeleton can be found in sesterterpenes isolated from Aleuritopteris ferns. These results provide insight into sesterterpene biosynthesis in Aleuritopteris ferns.

Substrate specificity of undecaprenyl diphosphate synthase from the hyperthermophilic archaeon Aeropyrum pernix.

Cis-prenyltransferase from a hyperthermophilic archaeon Aeropyrum pernix was expressed in Escherichia coli and purified for characterization. Properties such as substrate specificity, product chain-length, thermal stability and cofactor requirement were investigated using the recombinant enzyme. In particular, the substrate specificity of the enzyme attracts interest because only dimethylallyl diphosphate and geranylfarnesyl diphosphate, both of which are unusual substrates for known cis-prenyltransferases, are likely available as an allylic primer substrate in A. pernix. From the enzymatic study, the archaeal enzyme was shown to be undecaprenyl diphosphate synthase that has anomalous substrate specificity, which results in a preference for geranylfarnesyl diphosphate. This means that the product of the enzyme, which is probably used as the precursor of the glycosyl carrier lipid, would have an undiscovered structure.