Analogues of geranyl pyrophosphate as inhibitors of prenyltransferase

Preparation, characterization, and optimization of an in vitro C30 carotenoid pathway

The ispA gene encoding farnesyl pyrophosphate (FPP) synthase from Escherichia coli and the crtM gene encoding 4,4'-diapophytoene (DAP) synthase from Staphylococcus aureus were overexpressed and purified for use in vitro. Steady-state kinetics for FPP synthase and DAP synthase, individually and in sequence, were determined under optimized reaction conditions. For the two-step reaction, the DAP product was unstable in aqueous buffer; however, in situ extraction using an aqueous-organic two-phase system resulted in a 100% conversion of isopentenyl pyrophosphate and dimethylallyl pyrophosphate into DAP. This aqueous-organic two-phase system is the first demonstration of an in vitro carotenoid synthesis pathway performed with in situ extraction, which enables quantitative conversions. This approach, if extended to a wide range of isoprenoid-based pathways, could lead to the synthesis of novel carotenoids and their derivatives.

Purification, enzymatic characterization, and inhibition of the Z-farnesyl diphosphate synthase from Mycobacterium tuberculosis

We have recently shown that open reading frame Rv1086 of the Mycobacterium tuberculosis H37Rv genome sequence encodes a unique isoprenyl diphosphate synthase. The product of this enzyme, omega,E,Z-farnesyl diphosphate, is an intermediate for the synthesis of decaprenyl phosphate, which has a central role in the biosynthesis of most features of the mycobacterial cell wall, including peptidoglycan, arabinan, linker unit galactan, and lipoarabinomannan. We have now purified Z-farnesyl diphosphate synthase to near homogeneity using a novel mycobacterial expression system. Z-Farnesyl diphosphate synthase catalyzed the addition of isopentenyl diphosphate to omega,E-geranyl diphosphate or omega,Z-neryl diphosphate yielding omega,E,Z-farnesyl diphosphate and omega,Z,Z-farnesyl diphosphate, respectively. The enzyme has an absolute requirement for a divalent cation, an optimal pH range of 7-8, and K(m) values of 124 micrometer for isopentenyl diphosphate, 38 micrometer for geranyl diphosphate, and 16 micrometer for neryl diphosphate. Inhibitors of the Z-farnesyl diphosphate synthase were designed and chemically synthesized as stable analogs of omega,E-geranyl diphosphate in which the labile diphosphate moiety was replaced with stable moieties. Studies with these compounds revealed that the active site of Z-farnesyl diphosphate synthase differs substantially from E-farnesyl diphosphate synthase from pig brain (Sus scrofa).

Inhibition of farnesyl transferases from malignant and non-malignant cultured human lymphocytes by prenyl substrate analogues

Cytosolic prenyl transferases from two human lymphoid tissue-derived cell lines, IM-9 and Molt-4 cells, are shown to isoprenylate recombinant p21H-ras. Isoprenylation was inhibited by an N-acetylated pentapeptide (N-Ac-Lys-Cys-Val-Leu-Ser), c,t-farnesyl diphosphate, c,t,t-geranylgeranyl diphosphate, t,t,t-geranylgeranyl diphosphate and a photolabile farnesyl diphosphate analogue. c,t-Farnesyl and t,t,t-geranylgeranyl monophosphates were also effective inhibitors of the Molt-4 enzyme but not the IM-9 enzyme.

Undecaprenyl pyrophosphate synthetase from Lactobacillus plantarum: a dimeric protein

a++Undecaprenyl pyrophosphate synthetase has been purified from Lactobacillus plantarum. It catalyzes the formation of a C55 polyprenyl pyrophosphate having isoprene residues with cis stereochemistry. The enzyme was shown to be an acidic protein (pI = 5.1), which can be partially purified by preparative gel electrophoresis and Blue-agarose column chromatography. The Km's of the enzyme for its substrates t,t-farnesyl pyrophosphate and isopentenyl pyrophosphate were determined to be 0.13 and 1.92 microM, respectively. The molecular weight of the enzyme was estimated by molecular sieve chromatography and gradient centrifugation to be 56,000 +/- 4000. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the protein was composed of a dimer of 30,000-Da subunits. The enzyme was inactivated by the arginine-specific reagents phenylglyoxal, butanedione and, cyclohexanedione, but this inactivation was not prevented by either of the substrates.

Human liver prenyltransferase and its characterization

Prenyltransferase (dimethylallydiphosphate: isopentenyldiphosphate dimethylallytransferase, EC 2.5.1.1) has been purified to homogeneity from human liver obtained at autopsy. The enzyme is a dimer with a native molecular weight of 74 000 +/- 1 400. The amino acid composition is reported. the enzyme has a broad pH optimum between 7.3 and 8.8 and an absolute requirement for either Mn2+ or Mg2+ for activity; half-maximal activity was observed at 3.7 microM Mn2+ or 89.0 microM Mg2+. Michaelis constants for geranyl pyrophosphate and isopentenyl pyrophosphate were 0.44 and 0.94 microM, respectively; the V value for synthesis of farnesyl pyrophosphate from these substrates was 1.1 mumol . min-1 . mg-1. Isopentenyl pyrophosphate inhibited the reaction rates at concentrations above 2 microM when the concentrations of geranyl pyrophosphate were less than 2 microM. The highest concentration of geranyl pyrophosphate tested, 16 microM, showed no inhibition of reaction rates even when the concentration of isopentenyl pyrophosphate was as low as 0.2 microM. Only one form of human liver prenyltransferase could be observed under conditions which resolved the porcine enzyme into two distinct forms; the human enzyme is akin, physico-chemically, to the B-form of the pig liver enzyme. After dialysis against Tris-HCl buffer, pH 7.8, the enzyme became completely dependent upon dithiols or thiols for its activity. Kinetic experiments with a partially activated enzyme sample showed that the activation by the dithiol greatly enhanced the affinity of the enzyme for geranyl pyrophosphate, but not that for isopentenyl pyrophosphate. The human prenyltransferase is inactivated by phenylglyoxal according to pseudo-first-order kinetics, but is protected against the inactivation by 3,3-dimethylallyl and geranyl pyrophosphate. It is also inactivated by high concentrations (greater than 2 mM) of iodoacetic acid, but is protected against the inactivation by dithiothreitol. Antibodies raised to the B-form of the pig liver enzyme cross-reacted with the human prenyltransferase and were 47% as effective in precipitating the human enzyme as the porcine enzyme. In double immunodiffusion experiments the antiserum was monospecific against the B-form of the porcine enzyme; it also gave a single precipitin line with the A-form, but not identical with that given by the B-form. It gave a precipitin line also with the human enzyme, but not identical with that given by either the A- or B-form of the porcine enzyme.

Characterization of liver prenyl transferase and its inactivation by phenylglyoxal

The two interconvertible forms of pig liver prenyl transferase, A and B, consist of two identical subunits of Mr = 38 500 and are dimers. Form A contains six titratable SH-groups, whereas form B contains only four per dimer. The amino acid composition of the two forms is otherwise identical. Both enzyme forms are inactivated by phenylglyoxal. The inactivation in the absence of Mg2+ or Mn2+ is biphasic, each phase following pseudo first-order kinetics and is accompanied by a proportional binding of [14C]phenylglyoxal to the protein. In the initial fast phase of inactivation (t1/2 = 9.6 min) the amount of [14C]phenylglyoxal bound to the enzyme extrapolated to 1.1 arginyl residues and in the second phase (t1/2 = 23 min) to 2.2 arginyl residues modified per subunit for complete inactivation. 1 mM Mg2+ and 0.1 mM Mn2+ abolished the initial fast rate of inactivation and reduced its rate to a single half-life of about 60 min. Even at this slow rate of inactivation in the presence of Mg2+, the amount of [14C]phenylglyoxal bound to the enzyme extrapolated to about 2.3 arginyl residues modified per subunit for complete inactivation. In the absence of Mg2+ or Mn2+ only 1 mM geranyl pyrophosphate protected the enzyme against inactivation. However, in the presence of 1 mM Mg2+, isopentenyl, dimethylallyl and geranyl pyrophosphates gave additional protection over that observed with the metal ions, geranyl pyrophosphate being the most effective at 0.1 mM concentration.

Inhibition of liver prenyltransferase by alkyl phosphonates and phosphonophosphates

n-Pentyl and n-decyl phosphonate and the corresponding phosphonophosphates were found to inhibit cholesterol synthesis from mevalonate in the 10000 X g supernatants of liver homogenates and the synthesis of farnesyl pyrophosphate from geranyl and isopentenyl pyrophosphate by purified liver prenyltransferase. Kinetic analysis of the inhibition of prenyltransferase showed that the phosphonates and the phosphonophosphates interacted with two forms, or two sites, of the enzyme. The order of increasing potency was C5-phosphonate less than C10-phosphonate less than C5-phosphonophosphate less than C10-phosphonophosphate. The phosphonophosphates were at least ten times stronger inhibitors than the phosphonates.

Biosynthesis of geraniol and nerol and beta-D-glucosides in Pelargonium graveolens and Rosa dilecta

1. 3R-[2-(14)C]Mevalonate was incorporated into geranyl and neryl beta-d-glucosides in petals of Rosa dilecta in up to 10.6% yield, and the terpenoid part was specifically and equivalently labelled in the moieties derived from isopentenyl pyrophosphate and 3,3-dimethylallyl pyrophosphate. A similar labelling pattern, with incorporations of 0.06-0.1% was found for geraniol or nerol formed in leaves of Pelargonium graveolens The former results provide the best available evidence for the mevalonoid route to regular monoterpenes in higher plants. 2. Incorporation studies with 3RS-[2-(14)C,(4R)-4-(3)H(1)]-mevalonate and its (4S)-isomer showed that the pro-4R hydrogen atom of the precursor was retained and the pro-4S hydrogen atom was eliminated in both alcohols and both glucosides. These results suggest that the correlation of retention of the pro-4S hydrogen atom of mevalonate with formation of a cis-substituted double bond, such as has been found in certain higher terpenoids, does not apply to the biosynthesis of monoterpenes. It is proposed that either nerol is derived from isomerization of geraniol or the two alcohols are directly formed by different prenyltransferases. Possible mechanisms for these processes are discussed. 3. The experiments with [(14)C,(3)H]mevalonate also show that in these higher plants, as has been previously found in animal tissue and yeast, the pro-4S hydrogen atom of mevalonate was lost in the conversion of isopentenyl pyrophosphate into 3,3-dimethylallyl pyrophosphate.

Artificial substrates for prenyltransferase

Four out of 16 new allylic pyrophosphates synthesized were found to be artificial substrates for liver prenyltransferase (EC 2.5.1.1). These were the trans-and the cis-3-ethyl-3-methylallyl, the 3,3-diethylallyl and the (mixture of cis and trans) 3-methyl-3-n-propylallyl pyrophosphates. The products synthesized from these substrates and isopentenyl pyrophosphate were the appropriate homo- and bishomo-farnesyl pyrophosphates. Substitution of 3,3-dimethylallyl pyrophosphate at C-2 with a methyl group destroyed its reactivity with the enzyme. Neither the unsubstituted allyl pyrophosphate nor the cis- or trans-3-methylallyl pyrophosphate could be condensed with isopentenyl pyrophosphate. Thus the simplest allylic substrate for prenyltransferase is 3,3-dimethylallyl pyrophosphate.

Synthesis of 10,11-dihydrofarnesyl pyrophosphate from 6,7-dihydrogeranyl pyrophosphate by prenyltransferase

The syntheses of 6,7-dihydrogeraniol and of its pyrophosphate are described. It is shown that this analogue of geranyl pyrophosphate is a substrate for liver prenyltransferase and that the product synthesized by this enzyme from it and isopentenyl pyrophosphate is 10,11-dihydrofarnesyl pyrophosphate. The K(m) value for 6,7-dihydrogeranyl pyrophosphate was determined to be 1.11+/-0.19mum as compared with 4.34+/-1.71mum for geranyl pyrophosphate. The maximum reaction velocity with the artifical substrate was, however, only about one-fourth of that observed with geranyl pyrophosphate. The binding of isopentenyl pyrophosphate to the enzyme was not affected by the artificial substrate.