Farnesyl pyrophosphate synthase

The IBP and its products are displayed in Figure 12.1. HMG-CoA, ultimately derived from acetyl-CoA is converted to mevalonate via the enzyme HMG-CoA reductase (HMGR) [8]. This reaction is the rate-limiting step in the pathway. Mevalonate is then phosphorylated via mevalonate kinase (MK) to yield 5-phosphomevalonate [9]. IPP is formed following additional phosphorylation and decarboxylation steps [10]. Isomerization of IPP via the enzyme IPP isomerase yields DMAPP [11]. In mammals, the enzyme farnesyl pyrophosphate synthase (FDPS) catalyzes the synthesis of both GPP and FPP [12]. In plants, a separate GPP synthase has been identified [13]. GPP is a key intermediate in plants as it serves as the precursor for all monoterpenes. In animals, however, GPP appears to serve only as an intermediate in the synthesis of FPP. Very low basal levels of GPP have been measured in cell culture, although cellular GPP levels can become markedly increased in the setting of FDPS inhibition [14]. 

Montalvetti, A., Bailey, B.N., Martin, M.B., Severin, G.W., Oldfield, E., and Docampo, R. (2001). Bisphosphonates are potent inhibitors of Trypanosoma cruzi farnesyl pyrophosphate synthase. J Biol Chem 276 33930-33937. 

FPPS farnesyl pyrophosphate synthase ICAM intercellular cell adhesion molecule... 

Marini F, Falchetti A, Silvestri S et al (2008) Modulatory effect of farnesyl pyrophosphate synthase (FDPS) rs2297480 polymorphism on the response to long-term amino-bisphosphonate treatment in postmenopausal osteoporosis. Curr Med Res Opin 24 2609-2615... 

Montalvetti A, et al. (2003). Farnesyl pyrophosphate synthase is an essential enzyme in Trypanosoma brucei. In vitro RNA interference and in vivo inhibition studies. /. Biol. Chem. 278(19) 17075-17083. 

Mukherjee, P., Desai, P.V., Srivastava, A., Tekwani, B.L., and Avery, M.A. (2008) Probing the structures of leishmanial farnesyl pyrophosphate synthases homology modeling and docking studies. Journal of Chemical Information and Modeling, 48 (5), 1026-1040. 

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. 

Squalene takes part in metabolism as precursor for synthesis of steroids and structurally quite similar to (3-carotene, coenzyme qlO, vitamins Ki, E, and D. The squalene in skin and fat tissue comes from endogenous cholesterol synthesis as well as dietary resources in people who consume high amounts of olive and fish oil especially shark liver (Gershbein and Singh, 1969). Squalene is synthesized by squalene synthase which converts two units of farnesyl pyrophosphate, direct precursor for terpenes and steroids, into squalene. As a secosteroid, vitamin D biosynthesis is also regulated by squalene. Moreover, being precursor for each steroid family makes squalene a crucial component of the body. 

Overhand, M., Pieterman, E., Cohen, L.H., Valentijn, A.R.P.M., VanDerMarel, G.A., and vanBoom, J.H. (1997). Synthesis of triphosphonate analogues of farnesyl pyrophosphate, inhibitors of squalene synthase and protein farnesyl transferase. Bioorg Med Chem Lett 7 2435-2440. 

Further biosynthetic studies by Cane et have shown that the conversion of farnesyl pyrophosphate (15) into nerolidyl pyrophosphate (16) proceeds by a net syn (suprafacial) process and that the subsequent cyclization to cyclonerodiol (17) occurs in a trans manner (Scheme 4). This careful piece of work was achieved by incorporation studies with doubly labelled nerolidol and mevalonate precursors and then by ascertaining the chirality of the acetate derived by Kuhn-Roth oxidation through enzymatic conversion (malate synthase/fumarase incubation) into labelled malate. In a subsequent series of experiments with labelled precursors, Cane et have confirmed that (i) only the C-7 hydroxy-group in cyclonerodiol is derived from water whereas the C-3 hydroxy-group is derived... 

Terpene cyclase enzymes catalyze the cychzation of allylic pyrophosphate substrates to form carbocyclic products via car-bocation reaction intermediates. One well-studied example is pentalenene synthase (11, 12), which catalyzes the cychzation of farnesyl pyrophosphate to give pentalenene, whose reaction mechanism is shown in Fig. 15. Cychzation of farnesyl pyrophosphate is proposed to form an 11-membered intermediate, humulene, which is followed by a five-membered ring closure to form a bicychc tertiary carbocation. 1,2-Hydride migration followed by an additional five-membered ring closure gives a tricyclic carbocation, which gives pentalenene, at elimination. 

IPPP, a nucleophile (by virtue of its terminal vinyl group), and DMAPP, an electrophile, undergo condensation with elimination of pyrophosphate to yield geranyl pyrophosphate (an electrophile), which condenses with a molecule of IPPP to yield a farnesyl pyrophosphate and pyrophosphate. These reactions are probably catalyzed by the same cytosolic enzyme complex. Two molecules of farnesyl pyrophosphate and then condense head-to-head to form squalene by action of microsomal squalene synthase (Figure 19-14). 

The last step in the synthesis of squalene is a reductive taii-to-tail condensation of two molecules of farnesyl pyrophosphate catalyzed by the endoplasmic reticulum enzyme squalene synthase. 

The head-to-head union of two farnesyl pyrophosphate molecules to produce squalene is promoted by squalene synthase (33). The enzyme utilizes NADPH as a cofactor. If the cofactor is omitted, another species, presqualene pyrophosphate, accumulates (34). On addition of NADPH, this is converted to squalene. The structure of presqualene pyrophosphate was elucidated by Epstein and Rilling, who found that the material contains a highly substituted cyclopropane ring as a central feature (35). Poulter and associates (36), as well as van Tamelen and... 

Squalene synthase is an enzyme catalyzing the formation of squalene from farnesyl diphosphate which is a committed step in the cholesterol biosynthetic pathway. Therefore, squalene synthase is considered a better target than HMG-CoA reductase because farnesyl pyrophosphate, a downstream product of HMG-CoA reductase, is needed for prenylation of proteins and for the biosyntheses of ubiquinone and dolichol (Fig. 2). Before squalestatins and zaragozic acids were discovered, a number of squalene synthase inhibitors were synthesized that showed respectable inhibitory potencies in vitro, but none were successful in animal testing [41]. It was the discovery of squalestatins and zaragozic acids that renewed interest in this biological target, and at picomolar potencies they were the most active inhibitors of squalene synthase. 

Two molecules of farnesyl pyrophosphate form squalene, a 30-carbon compound. The reaction is catalyzed by the enzyme squalene synthase, which joins the two molecules in a tail-to-tail linkage. Squalene is the precursor of cholesterol, and cholesterol is the precursor of all other steroids. 

Squalene is built from two farnesyl pyrophosphate molecules. The reaction is catalyzed by squalene synthase and includes the formation of presqualene pyrophosphate and the stereospecific reduction of one of the precursor farnesyl pyrophosphates by the 4s-hydrogen of NADPH (C 2.1.1). 

Scheme 5.28 Cascade process in S. cerevisiae toward the artimisinin precursor artemisinic acid. Pathway engineering yields amorpha-4,n-diene via farnesyl pyrophosphate (FPP), and oxidations of amorphadiene are catalyzed by CYP71AV1 (redox partner protein not shown), alcohol dehydrogenase ADHl, and aldehyde dehydrogenase ALDHl. Artemisinin is synthesized in vitro from the produced artemisinic acid by established Synthetic chemistry. ADS, amorphadiene synthase.

---