Geranyl diphosphate synthase GPPS

Geranyl diphosphate synthase (GPPS E.C 2.5.1.1) catalyzes the condensation of isopentenyl diphosphate with dimethylallyl diphosphate to give a CIO compound, geranyl diphosphate, which is the universal precursor of all monoterpenoids. Fig. (6) [314]. 

Fig. 1.6 Phylogenetic tree of gymnosperm and angiosperm isoprenyl diphosphate synthase sequences. The isolated Picea ahies sequences are marked other isoprcnyl diphosphate synthases sequences are listed according to the major reaction product of the recombinant protein. Abbreviations GPP synthase, geranyl diphosphate synthase FPP synthase, famesyl diphosphate synthase and GGPP synthase, geranyl geranyl diphosphate synthase large su, large subunit of protein small su, small subunit of protein.

Upon the synthesis of IPP (C5) and its isomer DMAPP (C5) by either MVA or DXP pathways, the next step is chain elongation. The carbonium ion is a potent alkylating agent that can react with IPP (three molecules of IPP converted into one molecule of geranyl diphosphate (GPP) by condensation reaction catalyzed by enzyme geranyl diphosphate synthase), to yield geranyl diphosphate (GPP). Famesyl pyrophosphate synthase (EPS) is the prenyltransferase that catalyzes l -4 condensation reactions of IPP with the allylic diphosphates, dimethylallyl diphosphate (DMAPP), to produce famesyl pyrophosphate (FPP). 

Fig. 99.1 Proposed biosynthetic pathway of artemisinin in Artemisia annua L. plant. SQS Squalene synthase, ADS amorpha-4,11-diene synthase, FPP Famesyl diphosphate, FPS Famesyl pyrophosphate synthase, GPP Geranyl diphosphate, GPPS Geranyle diphosphate synthase, GS germaciene A synthase, DMAPP Dimethylallyl diphosphate, IPP isopeniraiyl diphosphate, CPS P-caryophyllene synthase, DBR2 double bond reductase 2, ECS epi-cedrol synthase, FPP fanesyl diphosphate, PS (E)-P-famesene synthase (Drawn based on informatitm published by Abdin et al., [18] and Zhang et al., 2005)...

The functional isoprene units in biological systems are DMAPP and its isomer IPP. Depending on the number of isoprene subunits, one differentiates between hemi- (C5), mono- (C q), sesqui- (Cu), di- (C20), sester- (C25), tri- (Cjg), tetrater-penes (C g), and polyterpenes (Cg) (Figure 16.7). Condensation of DMAPP with IPP by geranyl-diphosphate synthase (EC 2.5.1.1) produces geranyl-pyrophosphate (GPP) as a monoterpene. Subsequent condensation of GPP with IPP by farnesyl-diphosphate synthase (EC 2.5.1.92) yields farnesyl-diphosphate... 

Figure 10.7 All terpenes are derived from allylic diphosphates which are polymers of repeating isopentyl units (IPP) put together by the action of prenyltransferases. In plants, IPP can be derived from the mevalonate biosynthetic pathway (a cytoplasmic pathway) or the methyl erythritol phosphate pathway (a plastidic pathway). Monoterpenes are then derived from the CIO precursor geranyl diphosphate (GPP), sesquiterpenes from the C15 precursor famesyl diphosphate (FPP), and diterpenes from the C20 precursor geranylgeranyl diphosphate (GGPP) by the action of terpene synthases or cyclases, which divert carbon into the specific branch pathways.

Fig. 4 Reconstruction of the carotenoids biosynthetic pathway in S. cerevisiae. Heterologous activities t-HMGl 3 hydroxy-3-methylglutaryl-coenzymeA, ctrE geranylgeranyldiphosphate synthase (from Xanthophyllomyces dendrorhous), Ctrl phytoene desaturase, ctrYB bifunctional enzyme phytoene synthase and lycopene cyclase. Endogenous yeast activities ISIS I geranylgeranyldiphosphate synthase. Metabolites IPP isopentenyl diphosphate, GPP geranyl diphosphate, FPP famesyl-diphosphate, GGPP geranylgeranyl diphosphate...

In the biosynthesis of steroids lanosterol and cycloartenol, the building blocks DMAPP and IPP are first joined through famesyl diphosphate synthase to form geranyl pyrophosphate (GPP) and then to form FPP, presqualene pyrophosphate, squalene, and (S)-squalene-2,3-epoxide by corresponding enzymes, sequentially. The product (S)-squalene-2,3-epoxide is used to synthesize the sterols lanosterol (in animals) and cycloartenol (in plants) by lanosterol synthase and cycloartenol synthase, respectively [3]. Further, lanosterol and cycloartenol are converted into other steroids through steroidogenesis. 

Fig. 6 Different species-specific fates of linalool produced via ectopic expression of Clarkia breweri lina-lool synthase (LIS) [132] in tomato [200], petunia [187] and carnation [188]. GPP, geranyl diphosphate...

---