Isopentenyl pyrophosphate isomerase and prenyltransferase from tomato fruit plastids

HbIDI, SlIDI and EcIDI: A comparative study of isopentenyl diphosphate isomerase activity and structure

In this study, we cloned, expressed and purified the isopentenyl diphosphate isomerases (IDIs) from two plants, Hevea brasiliensis and Solanum lycopersicum, and compared them to the already well characterized Escherichia coli IDI. Phylogenetic analysis showed high homology between the three enzymes. Their catalytic activity was investigated in vitro with recombinant purified enzymes and in vivo by complementation colorimetric tests. The three enzymes displayed consistent activities both in vitro and in vivo. In term of structure, studied by ATR-FTIR and molecular modeling, it is clear that both plant enzymes are more related to their human homologue than to E. coli IDI. But it is assumed that EcIDI represent the minimalistic part of the catalytic core, as both plant enzymes present a supplementary sequence forming an extra α-helice surrounding the catalytic site that could facilitate the biocatalysis. New potential biotechnological applications may be envisaged.

The tomato cis-prenyltransferase gene family

cis-prenyltransferases (CPTs) are predicted to be involved in the synthesis of long-chain polyisoprenoids, all with five or more isoprene (C5) units. Recently, we identified a short-chain CPT, neryl diphosphate synthase (NDPS1), in tomato (Solanum lycopersicum). Here, we searched the tomato genome and identified and characterized its entire CPT gene family, which comprises seven members (SlCPT1-7, with NDPS1 designated as SlCPT1). Six of the SlCPT genes encode proteins with N-terminal targeting sequences, which, when fused to GFP, mediated GFP transport to the plastids of Arabidopsis protoplasts. The SlCPT3-GFP fusion protein was localized to the cytosol. Enzymatic characterization of recombinant SlCPT proteins demonstrated that SlCPT6 produces Z,Z-FPP, and SlCPT2 catalyzes the formation of nerylneryl diphosphate while SlCPT4, SlCPT5 and SlCPT7 synthesize longer-chain products (C25-C55). Although no in vitro activity was demonstrated for SlCPT3, its expression in the Saccharomyces cerevisiae dolichol biosynthesis mutant (rer2) complemented the temperature-sensitive growth defect. Transcripts of SlCPT2, SlCPT4, SlCPT5 and SlCPT7 are present at low levels in multiple tissues, SlCPT6 is exclusively expressed in red fruit and roots, and SlCPT1, SlCPT3 and SlCPT7 are highly expressed in trichomes. RNAi-mediated suppression of NDPS1 led to a large decrease in β-phellandrene (which is produced from neryl diphosphate), with greater reductions achieved with the general 35S promoter compared to the trichome-specific MKS1 promoter. Phylogenetic analysis revealed CPT gene families in both eudicots and monocots, and showed that all the short-chain CPT genes from tomato (SlCPT1, SlCPT2 and SlCPT6) are closely linked to terpene synthase gene clusters.

Inactivation of sll1556 in Synechocystis strain PCC 6803 impairs isoprenoid biosynthesis from pentose phosphate cycle substrates in vitro

In cyanobacteria many compounds, including chlorophylls, carotenoids, and hopanoids, are synthesized from the isoprenoid precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate. Isoprenoid biosynthesis in extracts of the cyanobacterium Synechocystis strain PCC 6803 grown under photosynthetic conditions, stimulated by pentose phosphate cycle substrates, does not appear to require methylerythritol phosphate pathway intermediates. The sll1556 gene, distantly related to type 2 IPP isomerase genes, was disrupted by insertion of a Kanr cassette. The mutant was fully viable under photosynthetic conditions although impaired in the utilization of pentose phosphate cycle substrates. Compared to the parental strain the Deltasll1556 mutant (i) is deficient in isoprenoid biosynthesis in vitro with substrates including glyceraldehyde-3-phosphate, fructose-6-phosphate, and glucose-6-phosphate; (ii) has smaller cells (diameter ca. 13% less); (iii) has fewer thylakoids (ca. 30% less); and (iv) has a more extensive fibrous outer wall layer. Isoprenoid biosynthesis is restored with pentose phosphate cycle substrates plus the recombinant Sll1556 protein in the Deltasll1556 supernatant fraction. IPP isomerase activity could not be demonstrated for the purified Sll1556 protein under our in vitro conditions. The reduction of thylakoid area and the effect on outer wall layer components are consistent with an impairment of isoprenoid biosynthesis in the mutant, possibly via hopanoid biosynthesis. Our findings are consistent with an alternate metabolic shunt for biosynthesis of isoprenoids.

Isoprenoid biosynthesis in Synechocystis sp. strain PCC6803 is stimulated by compounds of the pentose phosphate cycle but not by pyruvate or deoxyxylulose-5-phosphate

The photosynthetic cyanobacterium Synechocystis sp. strain PCC6803 possesses homologs of known genes of the non-mevalonate 2-C-methyl-D-erythritol 2-phosphate (MEP) pathway for synthesis of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Isoprenoid biosynthesis in extracts of this cyanobacterium, measured by incorporation of radiolabeled IPP, was not stimulated by pyruvate, an initial substrate of the MEP pathway in Escherichia coli, or by deoxyxylulose-5-phosphate, the first pathway intermediate in E. coli. However, high rates of IPP incorporation were obtained with addition of dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (GA3P), as well as a variety of pentose phosphate cycle compounds. Fosmidomycin (at 1 micro M and 1 mM), an inhibitor of deoxyxylulose-5-phosphate reductoisomerase, did not significantly inhibit phototrophic growth of the cyanobacterium, nor did it affect [(14)C]IPP incorporation stimulated by DHAP plus GA3P. To date, it has not been possible to unequivocally demonstrate IPP isomerase activity in this cyanobacterium. The combined results suggest that the MEP pathway, as described for E. coli, is not the primary path by which isoprenoids are synthesized under photosynthetic conditions in Synechocystis sp. strain PCC6803. Our data support alternative routes of entry of pentose phosphate cycle substrates derived from photosynthesis.

Partial purification of a farnesyl diphosphate synthase from whole-body Manduca sexta

Farnesyl diphosphate synthase (FPP synthase) is a ubiquitous enzyme that is required for the biosynthesis of sesquiterpenes, dolichols ubiquinones, and prenylated proteins in insects. We report on the partial purification and characterization of an FPP synthase, obtained from whole-body preparations of the lepidopteran insect, Manduca sexta. The larval enzyme was separated from isopentenyl diphosphate (IPP) isomerase, phosphatase, and GGPP synthase by preparative isoelectric focusing, and was further purified by DEAE Sepharose, hydroxyapatite, and size exclusion chromatography. Whole-body M. sexta FPP synthase has a native molecular weight of 60.5+/-3.5 kDa and consists of two subunits of 28.5+/-0.5 kDa. As seen with other prenyltransferases, the enzyme has an absolute requirement for divalent cation and both Mn(2+) and Mg(2+) stimulated activity, although the former was inhibitory at higher concentrations. Insect FPP synthase catalyzes the condensation of IPP (K(m)=2.9+/-1.2 microM) with both dimethylallyl diphosphate and geranyl diphosphate (K(m)=0.8+/-0.4 microM). The enzyme requires the presence of detergent, glycerol, and non-specific protein-protein interactions for stability and maximum catalytic activity.

Isopentenyl diphosphate isomerase deficiency in Synechocystis sp. strain PCC6803

Isopentenyl diphosphate isomerase (IPP isomerase) in many organisms and in plastids is central to isoprenoid synthesis and involves the conversion between IPP and dimethylallyl diphosphate (DMAPP). It is shown that Synechocystis PCC6803 is deficient in IPP isomerase activity, consistent with the absence in its genome of an obvious homologue for the enzyme. Incorporation of [1-(14)C]IPP in cell extracts, primarily into C(20), occurs only upon priming with DMAPP in Synechocystis PCC6803 and in Synechococcus PCC7942. Isoprenoid synthesis in these cyanobacteria does not appear to involve interconversion of IPP and DMAPP, raising the possibility that they are not within the plastid evolutionary lineage.

Purification and characterization of two isoforms of isopentenyl-diphosphate isomerase from elicitor-treated Cinchona robusta cells

In Cinchona robusta (Rubiaceae) cell suspension cultures, the activity of the enzyme isopentenyl-diphosphate isomerase (isopentenyl-POP isomerase) is transiently induced after addition of a homogenate of the phytopathogenic fungus Phytophthora cinnamomi. The enzyme catalyses the interconversion of isopentenyl-POP and dimethylallyl diphosphate (dimethylallyl-POP) and may be involved in the biosynthesis of anthraquinone phytoalexins that accumulate rapidly after elicitation of Cinchona cells. From elicitor-treated C. robusta cells, two isoforms of isopentenyl-POP isomerase have been purified to apparent homogeneity in four chromatographic steps. The purified forms are monomeric enzymes of 34 kDa (isoform I) and 29 kDa (isoform II), with Km values for isopentenyl-POP of 5.1 microM and 1.0 microM, respectively. Both isoforms require Mn2+ or Mg2+ as cofactor, isoform II showing a preference for Mn2+ with maximum activity at 1.5-2 mM. Isoform I was most active in the presence of 0.5-1.5 mM Mg2+ or in the presence of 0.5 mM Mn2+. A pH optimum of 7-7.8 was found for both forms and both were competitively inhibited by geranyl diphosphate (Ki 96 microM for isoform I) and the transition state analogue 2-(dimethylamino)ethyl diphosphate. Rechromatography of purified isoforms did not indicate any interconversion of both forms. Western blot analysis, using antibodies raised against isopentenyl-POP isomerase purified from Capsicum annuum, showed the presence of both isoforms in the crude protein extracts from C. robusta cells. Isoform II was specifically induced by elicitation, non-treated cells contained low activity of this isoform. The possible role of isopentenyl-POP isomerase in the biosynthesis of anthraquinones is discussed.

Prenyltransferase compartmentation in cells of Vitis vinifera cultivated in vitro

Two prenyltransferases were located in cell cultures of Vitis vinifera. A geranyl pyrophosphate synthase (EC 2.5.1.1) was associated with plastid-like membranes whereas a farnesyl pyrophosphate synthase (EC 2.5.1.10) was found to be soluble.

Partial purification and properties of geranyl pyrophosphate synthase from Lithospermum erythrorhizon cell cultures

A prenyltransferase (EC 2.5.1.1) was isolated from cell cultures of Lithospermum erythrorhizon. The enzyme was purified 92-fold by subsequent chromatography on DEAE-Sephacel, phenyl-Sepharose, and Sephadex G-150. Geranyl pyrophosphate (GPP) was the sole product of the enzymatic reaction with dimethylallyl pyrophosphate and isopentenyl pyrophosphate as the substrates. The enzyme showed a molecular weight of 73,000, estimated by gel chromatography on Sephadex G-150, and an isoelectric point at pH 4.95, determined by analytical isoelectric focusing. It had an absolute requirement for a divalent cation with Mg2+ and Mn2+ being most effective. The enzyme was soluble rather than membrane-bound. The physiological role of this prenyltransferase probably is to supply GPP for the biosynthesis of shikonin. It is the first chain-length specific geranyl pyrophosphate synthase reported from eukaryotic cells.

Geranyl pyrophosphate synthase: characterization of the enzyme and evidence that this chain-length specific prenyltransferase is associated with monoterpene biosynthesis in sage (Salvia officinalis)

Cell-free homogenates from sage (Salvia officinalis) leaves convert dimethylallyl pyrophosphate and isopentenyl pyrophosphate to a mixture of geranyl pyrophosphate, farnesyl pyrophosphate, and geranylgeranyl pyrophosphate, with farnesyl pyrophosphate predominating. These prenyltransferase activities were localized primarily in the soluble enzyme fraction, and separation of this preparation on Sephadex G-150 revealed the presence of a partially resolved, labile geranyl pyrophosphate synthase activity. The product of the condensation reaction between [1-14C]dimethylallyl pyrophosphate and [1-3H]isopentenyl pyrophosphate was verified as [14C,1-3H]geranyl pyrophosphate by TLC isolation, enzymatic hydrolysis to geraniol, degradative studies, and the preparation of the crystalline diphenylurethane. The cis-isomer, neryl pyrophosphate, was not a product of the enzymatic reaction. By employing a selective tissue extraction procedure, the geranyl pyrophosphate synthase activity was localized in the leaf epidermal glands, the site of monoterpene biosynthesis, suggesting that the role of this enzyme is to supply the C10 precursor for the production of monoterpenes. Glandular extracts enriched in geranyl pyrophosphate synthase were partially purified by a combination of hydrophobic interaction chromatography on phenyl-Sepharose and gel permeation chromatography on Sephadex G-150. Substrate and product specificity studies confirmed the selective synthesis of geranyl pyrophosphate by this enzyme, which was also characterized with respect to molecular weight, pH optimum, cation requirement, inhibitors, and kinetic parameters, and shown to resemble other prenyltransferases.

Partial purification and characterization of two sesquiterpene cyclases from sage (Salvia officinalis) which catalyze the respective conversion of farnesyl pyrophosphate to humulene and caryophyllene

Humulene cyclase and caryophyllene cyclase, two enzymes which catalyze the cyclization of farnesyl pyrophosphate to the respective sesquiterpene olefins, have been partially purified from the supernatant fraction of a sage (Salvia officinalis) leaf epidermis extract and separated from each other by a combination of hydrophobic interaction, gel filtration, and ion-exchange chromatography. The molecular weight of both cyclases was estimated by gel filtration to be 57,000 and both cyclases exhibited a pH optimum of 6.5 and preferred Mg2+ (Km approximately 1.5 mM) as the required divalent metal cation. Both enzymes possessed a Km of about 1.7 microM for farnesyl pyrophosphate, were strongly inhibited by p-hydroxymercuribenzoate, and exhibited comparable sensitivities to a variety of other potential inhibitors. The properties of the two sesquiterpene olefin cyclases, which are the first from a higher plant source to be examined in detail, were very similar to each other and to other monoterpene, sesquiterpene, and diterpene cyclases previously described.