Bibenzyl synthase

PKSs are characterized by their ability to catalyze the formation of polyketide chains from the sequential condensation of acetate units from malonate thioesters. In plants they produce a range of natural products with varied in vivo and pharmacological properties. PKSs of particular note include acridone synthase, bibenzyl synthase, 2-pyrone synthase, and stilbene synthase (STS). STS forms resveratrol, a plant defense compound of much interest with regard to human health. STS shares high sequence identity with CHS, and is considered to have evolved from CHS more than once. ° Knowledge of the molecular structure of the CHS-like enzymes has allowed direct engineering of CHS and STS to alter their catalytic activities, including the number of condensations carried out (reviewed in Refs. 46, 51, 52). These reviews also present extensive, and superbly illustrated, discussions of CHS enzyme structure and reaction mechanism. 

Biosynthesis of dihydrophenanthrenes is similar to that of stilbenes but appears to involve dihydrocinnamic acid and the enzyme bibenzyl synthase, whereas the biosynthesis of phenanthrenes involves the corresponding unsaturated acids (Gorham, 1989). 

Gehlert, R. and H. Kindl, Induced formation of dihydrophenanthrenes and bibenzyl synthase upon destruction of orchid mycorrhiza. Phytochemistry, 30, 457-460 (1991). 

Type III polyketide synthases (PKS) form the primary scaffolds for the synthesis of a range of secondary metabolites including flavonoids, stilbenes, bibenzyls, xanthones and pyrones [19] (Fig. 2). They catalyze a reaction similar to their fatty acid synthase (FAS) ancestors by facilitating the sequential head-to-tail addition of two-carbon acetate units to a growing polyketide chain. Type III PKSs differ from their type I and type II relatives by a simpler structure and the use of a CoA thioester substrate instead of an acyl carrier protein (ACP)-linked substrate [19]. 

---