Biosynthesis of Value-Added Isoprene Derivatives

Isoprene is the common name for the chemical compound 2-methylbuta-l,3-diene. Conventionally, all natural compounds built up from isoprene subunits, (Cj) , are denoted as terpenes, therefore terpenes are also denoted as isoprenoids. Terpenes cover most of the range of natural products about 55000 terpenes are known at present in the literature. In Nature, terpenes occur predominantly as hydrocarbons, alcohols, and their glycosides, ethers, aldehydes, ketones, carboxylic acids, and esters [103]. 

Carotenoids are naturally occurring pigments synthesized as hydrocarbons (carotene, lycopene) or oxygenated derivatives (xanthophylls) by plants and microorganisms. Carotenoids have been successfully synthesized in several engineered strains [4, 85, 105—107]. Coexpression of GGPP synthase (crtE), phytoene synthase (crtB), and phytoenedesaturase crtl) is sufficient to convert IPP and farnesyl-diphosphate (FPP) to lycopene in . coli [106]. 

Another derivative is the zeatin. Zeatin belongs to the plant-growth hormones, cytokinins. Cytokinins are adenine derivatives with isoprenoid side chain [108, 109]. The rate-limiting step of tra/is-zeatin biosynthesis is catalyzed by adenylate-isopentenyltransferase (cytokinin synthase) [110]. The plant enzyme (EC 2.5.1.27) utilize ADP, which is different from the microbial one (EC 2.5.1.112) which recognizes ATP/or ADP [111, 112]. Afterward, the adenylate-isopentenyl converts to the active tra/is-zeatin by a single hydroxylation reaction (cytokinin tra/is-hydroxylase). On the opposite site, cis-zeatin biosynthesis starts with a different transferase, tRNA-dimethylallyl-transferase (EC 2.5.1.75) [113-116], which mediates the transfer of an isopentenyl group of DMAPP to adenine of tRNAs. 

An extra-interesting isoprene derivative is natural rubber. Natural rubber is a 

Whited, G.M., Feher, F.J., Benko, DA., Cervin, M.A. et al. (2010) Development of a gas-phase bioprocess for isoprene-monomer production using metabolic pathway engineering. Ind. BiotechnoL, 6 (3), 152-163. 

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