Protein farnesyltransferase isoprenoid substrate discrimination is dependent on isoprene double bonds and branched methyl groups

Enhancing the photosensitizing activity of natural flavins: Tuning the heavy-atom effect in the isoalloxazine series

Structure-photosensitizing activity relationships for a series of flavin analogues were investigated with the final goal of identifying the most potent photosensitizer in these series. The main structural modifications involved the introduction of various halogen atoms in C₇- and/or C₈-positions on the isoalloxazine ring. These compounds were synthesized by reacting judiciously-functionalized anilines with alloxan. The SAR trends showed that the photosensitizing activity increased with the size of the halogen atoms, confirming the importance of the heavy-atom effect on the photosensitizer's activity. The halogens in C₈ were more active than the di-substituted halogens, which in turn were more active than the C₇-substituted equivalents. However, even if the photosensitizing activity is slightly less important for the 7- compared to the 8-substituted derivatives, the 7-haloisoalloxazines are promising photosensitizers, as they present a better cellular toxicity profile than the 8-substituted analoges. The photosensitizing activity perfectly correlated with the determined fluorescence for the same compounds. Except for the dihalogeno derivatives, all the compounds were not toxic up to a 50 μM range.

Analyzing the postulated inhibitory effect of Manumycin A on farnesyltransferase

Manumycin A is postulated to be a specific inhibitor against the farnesyltransferase (FTase) since this effect has been shown in 1993 for yeast FTase. Since then, plenty of studies investigated Manumycin A in human cells as well as in model organisms like Caenorhabditis elegans. Some studies pointed to additional targets and pathways involved in Manumycin A effects like apoptosis. Therefore, these studies created doubt whether the main mechanism of action of Manumycin A is FTase inhibition. For some of these alternative targets half maximal inhibitory concentrations (IC₅₀) of Manumycin A are available, but not for human and C. elegans FTase. So, we aimed to 1) characterize missing C. elegans FTase kinetics, 2) elucidate the IC₅₀ and K_i values of Manumycin A on purified human and C. elegans FTase 3) investigate Manumycin A dependent expression of FTase and apoptosis genes in C. elegans. C. elegans FTase has its temperature optimum at 40°C with K_M of 1.3 µM (farnesylpyrophosphate) and 1.7 µM (protein derivate). Whilst other targets are inhibitable by Manumycin A at the nanomolar level, we found that Manumycin A inhibits cell-free FTase in micromolar concentrations (K_{i human} 4.15 μM; K_{i C. elegans} 3.16 μM). Furthermore, our gene expression results correlate with other studies indicating that thioredoxin reductase 1 is the main target of Manumycin A. According to our results, the ability of Manumycin A to inhibit the FTase at the micromolar level is rather neglectable for its cellular effects, so we postulate that the classification as a specific FTase inhibitor is no longer valid.

Impact of a conserved N-terminal proline-rich region of the α-subunit of CAAX-prenyltransferases on their enzyme properties

BACKGROUND

The CAAX-prenyltransferases farnesyltransferase (FTase) and geranylgeranyltransferase I (GGTase I) are heterodimers with a common α- (FTα) and unique β-subunits. Recently, α-subunits of species (e.g., human) that harbour an N-terminal proline-rich region (PRR) showed different dimerization behaviours than α-subunits without PRR (e.g., yeast). However, the specific function of the PRR has not been elucidated so far.

METHODS

To determine whether the PRR is a conserved motif throughout eukaryotes, we performed phylogenetics. Elucidating the impact of the PRR on enzyme properties, we cloned human as well as rat PRR deficient FTα, expressed them heterologously and compared protein-protein interaction by pull-down as well as crosslinking experiments. Substrate binding, enzyme activity and sensitivity towards common FTase inhibitors of full length and PRR-deletion α-subunits and their physiological partners was determined by continuous fluorescence assays.

RESULTS

The PRR is highly conserved in mammals, with an exception for marsupials harbouring a poly-alanine region instead. The PRR shows similarities to canonical SH3-binding domains and to profilin-binding domains. Independent of the PRR, the α-subunits were able to dimerize with the different physiological β-subunits in in vitro as well as in yeast two-hybrid experiments. FTase and GGTase I with truncated FTα were active. The K_M values for both substrates are in the single-digit µM range and show no significant differences between enzymes with full length and PRR deficient α-subunits within the species.

CONCLUSIONS

Our data demonstrate that an N-terminal PRR of FTα is highly conserved in mammals. We could show that the activity and inhibitability is not influenced by the truncation of the N-terminal region. Nevertheless, this region shows common binding motifs for other proteins involved in cell-signalling, trafficking and phosphorylation, suggesting that this PRR might have other or additional functions in mammals. Our results provide new starting points due to the relevant but only partly understood role of FTα in eukaryotic FTase and GGTase I. Video Abstract.

Cardiac decompensation and promiscuous prenylation of small GTPases in cardiomyocytes in response to local mevalonate pathway disruption

Investigations of major mevalonate pathway enzymes have demonstrated the importance of local isoprenoid synthesis in cardiac homeostasis. Farnesyl diphosphate synthase (FPPS) synthesizes isoprenoid precursors needed for cholesterol biosynthesis and protein prenylation. Wang, Zhang, Chen et al, in a recently published article in The Journal of Pathology, elegantly elucidated the pathological outcomes of FPPS deficiency in cardiomyocytes, which paradoxically resulted in increased prenylation of the small GTPases Ras and Rheb. Cardiomyocyte FPPS depletion caused severe dilated cardiomyopathy that was associated with enhanced GTP-loading and abundance of Ras and Rheb in lipidated protein-enriched cardiac fractions and robust activation of downstream hypertrophic ERK1/2 and mTOR signaling pathways. Cardiomyopathy and activation of ERK1/2 and mTOR caused by loss of FPPS were ameliorated by inhibition of farnesyltransferase, suggesting that impairment of FPPS activity results in promiscuous activation of Ras and Rheb through non-canonical actions of farnesyltransferase. Here, we discuss the findings and adaptive signaling mechanisms in response to disruption of local cardiomyocyte mevalonate pathway activity, highlighting how alteration in a key branch point in the mevalonate pathway affects cardiac biology and function and perturbs protein prenylation, which might unveil novel strategies and intricacies of targeting the mevalonate pathway to treat cardiovascular diseases. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cardiac-specific deletion of FDPS induces cardiac remodeling and dysfunction by enhancing the activity of small GTP-binding proteins

The mevalonate pathway is essential for cholesterol biosynthesis. Previous studies have suggested that the key enzyme in this pathway, farnesyl diphosphate synthase (FDPS), regulates the cardiovascular system. We used human samples and mice that were deficient in cardiac FDPS (c-Fdps^-/- mice) to investigate the role of FDPS in cardiac homeostasis. Cardiac function was assessed using echocardiography. Left ventricles were examined and tested for histological and molecular markers of cardiac remodeling. Our results showed that FDPS levels were downregulated in samples from patients with cardiomyopathy. Furthermore, c-Fdps^-/- mice exhibited cardiac remodeling and dysfunction. This dysfunction was associated with abnormal activation of Ras and Rheb, which may be due to the accumulation of geranyl pyrophosphate. Activation of Ras and Rheb stimulated downstream mTOR and ERK pathways. Moreover, administration of farnesyltransferase inhibitors attenuated cardiac remodeling and dysfunction in c-Fdps^-/- mice. These results indicate that FDPS plays an important role in cardiac homeostasis. Deletion of FDPS stimulates the downstream mTOR and ERK signaling pathways, resulting in cardiac remodeling and dysfunction. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Key Enzymes for the Mevalonate Pathway in the Cardiovascular System

ABSTRACT

Isoprenylation is an important post-transcriptional modification of small GTPases required for their activation and function. Isoprenoids, including farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate, are indispensable for isoprenylation by serving as donors of a prenyl moiety to small G proteins. In the human body, isoprenoids are mainly generated by the mevalonate pathway (also known as the cholesterol-synthesis pathway). The hydroxymethylglutaryl coenzyme A reductase catalyzes the first rate-limiting steps of the mevalonate pathway, and its inhibitor (statins) are widely used as lipid-lowering agents. In addition, the FPP synthase is also of critical importance for the regulation of the isoprenoids production, for which the inhibitor is mainly used in the treatment of osteoporosis. Synthetic FPP can be further used to generate geranylgeranyl pyrophosphate and cholesterol. Recent studies suggest a role for isoprenoids in the genesis and development of cardiovascular disorders, such as pathological cardiac hypertrophy, fibrosis, endothelial dysfunction, and fibrotic responses of smooth-muscle cells. Furthermore, statins and FPP synthase inhibitors have also been applied for the management of heart failure and other cardiovascular diseases rather than their clinical use for hyperlipidemia or bone diseases. In this review, we focus on the function of several critical enzymes, including hydroxymethylglutaryl coenzyme A reductase, FPP synthase, farnesyltransferase, and geranylgeranyltransferase in the mevalonate pathway which are involved in regulating the generation of isoprenoids and isoprenylation of small GTPases, and their pathophysiological role in the cardiovascular system. Moreover, we summarize recent research into applications of statins and the FPP synthase inhibitors to treat cardiovascular diseases, rather than for their traditional indications respectively.

Production of isoprene, one of the high-density fuel precursors, from peanut hull using the high-efficient lignin-removal pretreatment method

BACKGROUND

Isoprene as the feedstock can be used to produce renewable energy fuels, providing an alternative to replace the rapidly depleting fossil fuels. However, traditional method for isoprene production could not meet the demands for low-energy consumption and environment-friendliness. Moreover, most of the previous studies focused on biofuel production out of lignocellulosic materials such as wood, rice straw, corn cob, while few studies concentrated on biofuel production using peanut hull (PH). As is known, China is the largest peanut producer in the globe with an extremely considerable amount of PH to be produced each year. Therefore, a novel, renewable, and environment-friendly pretreatment strategy to increase the enzymatic hydrolysis efficiency of cellulose and reduce the inhibitors generation was developed to convert PH into isoprene.

RESULTS

The optimal pretreatment conditions were 100 °C, 60 min, 10% (w/v) solid loading with a 2:8 volume ratio of phosphoric acid and of hydrogen peroxide. In comparison with the raw PH, the hemicellulose and lignin were reduced to 85.0 and 98.0%, respectively. The cellulose-glucose conversion of pretreated PH reached up to 95.0% in contrast to that of the raw PH (19.1%). Only three kinds of inhibitors including formic acid, levulinic acid, and a little furfural were formed during the pretreatment process, whose concentrations were too low to inhibit the isoprene yield for Escherichia coli fermentation. Moreover, compared with the isoprene yield of pure glucose fermentation (298 ± 9 mg/L), 249 ± 6.7 and 294 ± 8.3 mg/L of isoprene were produced using the pretreated PH as the carbon source by the engineered strain via separate hydrolysis and fermentation and simultaneous saccharification and fermentation (SSF) methods, respectively. The isoprene production via SSF had a 9.8% glucose-isoprene conversion which was equivalent to 98.8% of isoprene production via the pure glucose fermentation.

CONCLUSIONS

The optimized phosphoric acid/hydrogen peroxide combination pretreatment approach was proved effective to remove lignin and hemicellulose from lignocellulosic materials. Meanwhile, the pretreated PH could be converted into isoprene efficiently in the engineered Escherichia coli. It is concluded that this novel strategy of isoprene production using lignocellulosic materials pretreated by phosphoric acid/hydrogen peroxide is a promising alternative to isoprene production using traditional way which can fully utilize non-renewable fossil sources.

Farnesyl diphosphate analogues with aryl moieties are efficient alternate substrates for protein farnesyltransferase

Farnesylation is an important post-translational modification essential for the proper localization and function of many proteins. Transfer of the farnesyl group from farnesyl diphosphate (FPP) to proteins is catalyzed by protein farnesyltransferase (FTase). We employed a library of FPP analogues with a range of aryl groups substituting for individual isoprene moieties to examine some of the structural and electronic properties of the transfer of an analogue to the peptide catalyzed by FTase. Analysis of steady-state kinetics for modification of peptide substrates revealed that the multiple-turnover activity depends on the analogue structure. Analogues in which the first isoprene is replaced with a benzyl group and an analogue in which each isoprene is replaced with an aryl group are good substrates. In sharp contrast with the steady-state reaction, the single-turnover rate constant for dansyl-GCVLS alkylation was found to be the same for all analogues, despite the increased chemical reactivity of the benzyl analogues and the increased steric bulk of other analogues. However, the single-turnover rate constant for alkylation does depend on the Ca(1)a(2)X peptide sequence. These results suggest that the isoprenoid transition-state conformation is preferred over the inactive E·FPP·Ca(1)a(2)X ternary complex conformation. Furthermore, these data suggest that the farnesyl binding site in the exit groove may be significantly more selective for the farnesyl diphosphate substrate than the active site binding pocket and therefore might be a useful site for the design of novel inhibitors.

Synthesis of Farnesol Analogues Containing Triazoles in Place of Isoprenes through 'Click Chemistry'

A solid-phase three-component Huisgen reaction has been used to generate polar farnesol and farnesyl diphosphate analogues. The Cu(I)-catalyzed 1,3-cycloadditions of various azides with solid supported (E)-3-methylhept-2-en-6-yn-1-ol provided only the 1,4-disubstituted 1,2,3-triazole regioisomers. The organic azides were generated in situ to minimize handling of potentially explosive azides. We have employed this powerful 'click chemistry' to make farnesol analogues where both β- and γ-isoprenes were replaced by triazole and substituted aromatic rings, respectively.

Protein farnesyltransferase-catalyzed isoprenoid transfer to peptide depends on lipid size and shape, not hydrophobicity

Protein farnesyl transferase (FTase) catalyzes transfer of a 15-carbon farnesyl group from farnesyl diphosphate (FPP) to a conserved cysteine in the C-terminal Ca(1)a(2)X motif of a range of proteins, including the oncoprotein H-Ras ("C" refers to the cysteine, "a" to any aliphatic amino acid, and "X" to any amino acid) and the lipid chain interacts with, and forms part of the Ca(1)a(2)X peptide binding site. Previous studies have shown that H-Ras biological function is ablated when it is modified with lipids that are 3-5 orders of magnitude less hydrophobic than FPP. Here, we employed a library of anilinogeranyl diphosphate (AGPP) and phenoxygeranyl diphosphate (PGPP) derivatives with a range of polarities (log P (lipid alcohol) = 0.7-6.8, log P (farnesol) = 6.1) and shapes to examine whether FTase-catalyzed transfer to peptide is dependent on the hydrophobicity of the lipid. Analysis of steady-state transfer kinetics for analogues to dansyl-GCVLS peptide revealed that the efficiency of lipid transfer was highly dependent on both the shape and size, but was independent of the polarity of the analogue. These observations indicate that hydrophobic features of isoprenoids critical for their association with membranes and/or protein receptors are not required for efficient transfer to Ca(1)a(2)X peptides by FTase. Furthermore, the results of these studies indicate that the role played by the farnesyl lipid in the FTase mechanism is primarily structural. To explain these results we propose a model in which the FTase active site stabilizes a membrane interface-like environment.

Synthesis and biochemical evaluation of 3,7-disubstituted farnesyl diphosphate analogues

Farnesyl diphosphate (FPP) analogues have proven to be both potent inhibitors of protein-farnesyltransferase (FTase) and valuable probes for the investigation of the function of prenylated proteins. Previously, we have demonstrated that certain 3-substituted and 7-substituted FPP analogues can act as inhibitors of FTase, while others are effective alternative substrates. We have now utilized our vinyl triflate-mediated route to synthesize the first seven FPP variants bearing substituents in both the 3- and 7-positions of the isoprene unit. Despite their exceptional steric bulk with respect to FPP itself, six of the seven analogues bind to FTase. Two of the analogues are potent inhibitors of the enzyme, but a more striking finding is that three FPP variants (4a, 4b, and 4f) are efficient alternative substrates for FTase.

Farnesyl diphosphate analogues with omega-bioorthogonal azide and alkyne functional groups for protein farnesyl transferase-catalyzed ligation reactions

Eleven farnesyl diphosphate analogues, which contained omega-azide or alkyne substituents suitable for bioorthogonal Staudinger and Huisgen [3 + 2] cycloaddition coupling reactions, were synthesized. The analogues were evaluated as substrates for the alkylation of peptide cosubstrates by yeast protein farnesyl transferase. Five of the diphosphates were good alternative substrates for farnesyl diphosphate (FPP). Steady-state kinetic constants were measured for the active compounds, and the products were characterized by HPLC and LC-MS. Two of the analogues gave steady-state kinetic parameters (kcat and Km) very similar to those of the natural substrate.

Lipidated ras and rab peptides and proteins--synthesis, structure, and function

Chemical biology can be defined as the study of biological phenomena from a chemical approach. Based on the analysis of relevant biological phenomena and their structural foundation, unsolved problems are identified and tackled through a combination of chemistry and biology. Thus, new synthetic methods and strategies are developed and employed for the construction of compounds that are used to investigate biological procedures. Solid-phase synthesis has emerged as the preferred method for the synthesis of lipidated peptides, which can be chemoselectively ligated to proteins of the Ras superfamily. The generated peptides and proteins have solved biological questions in the field of the Ras-superfamily GTPases that are not amendable to chemical or biological techniques alone.

Exploiting the substrate tolerance of farnesyltransferase for site-selective protein derivatization

The site-selective modification of proteins with a functional group is an important biochemical technique, but covalent attachment of a desired group to a chosen site is complicated by the reactivity of other amino acid side chains, often resulting in undesired side reactions. One potential solution to this problem involves exploiting the activity of protein-modifying enzymes that recognize a defined protein sequence. Protein farnesyltransferase (FTase) covalently attaches an isoprenoid moiety to a cysteine unit in the context of a short C-terminal sequence that can be easily grafted onto recombinant proteins. Here we describe the synthesis of four phosphoisoprenoids functionalized with biotin, azide, or diene groups. These phosphoisoprenoids bound to FTase with affinities comparable to that of the native substrate. With the exception of the biotin-functionalized analogue, all the phosphoisoprenoids generated could be transferred to peptide and protein substrates by FTase. Unlike proteins modified with farnesyl moieties, Ypt7 prenylated with (2E,6E)-8-(azidoacetamido)-3,7-dimethylocta-2,6-dienyl groups did not oligomerize and showed no detectable increase in hydrophobicity. To assess the suitability of the functionalized isoprenoids for protein modifications they were further derivatized, both by Diels-Alder cycloaddition with 6-maleimidohexanoic acid and by Staudinger ligation with a phosphine. We demonstrate that the Staudinger ligation proceeds more rapidly and is more efficient than the Diels-Alder cycloaddition. Our data validate the use of FTase as a protein-modification tool for biochemical and biotechnological applications.

Computational and conformational evaluation of FTase alternative substrates: insight into a novel enzyme binding pocket

Protein farnesyltransferase (FTase) is an important anticancer drug target. In an effort to develop isoprenoid diphosphate-based FTase inhibitors, striking variations have been observed in the ability of conservatively modified analogues to bind to the enzyme. For example, 2Z-GGPP is an alternative substrate with high binding affinity, while GGPP is not an alternative substrate. Using the availability of high-resolution FTase crystal structures, we have used pharmacophore and docking studies to elucidate a new binding pocket for isoprenoid analogues. The unique conformations between the first two isoprene units of 2Z-GGPP, but not GGPP, allows 2Z-GGPP to exploit this new binding pocket. The discovered conformation allows the molecule to adopt a reactive conformation while placing hydrophobic groups within the predominately hydrophobic binding pocket. This computational finding is supported by NMR studies on (13)C-labeled 2Z-farnesol, which confirm that the computationally predicted conformation is also favored in solution. These discoveries suggest that ligand conformational flexibility may be an important design consideration for the development of both inhibitors and alternative substrates of FTase.

Directed Library of Anilinogeranyl Analogues of Farnesyl Diphosphate via Mixed Solid- and Solution-Phase Synthesis

[reaction: see text]. A directed library of anilinogeranyl diphosphate analogues of the isoprenoid farnesyl diphosphate has been prepared by solid-phase organic synthesis using a traceless linker strategy in moderate yield in three steps: reductive amination, bromination, and treatment with ((n-Bu)4N)3HP2O7.

Synthesis and activity of fluorescent isoprenoid pyrophosphate analogues

New fluorescent analogues of farnesol and geranylgeraniol have been prepared and then converted to the corresponding pyrophosphates. These analogues incorporate anthranylate or dansyl-like groups anchored to the terpenoid skeleton through amine bonds that would be expected to be relatively stable to metabolism. After addition of the alcohols or the pyrophosphates to the culture medium, their fluorescence is readily observed inside a human-derived leukemia cell line. Enzyme assays have revealed that the farnesyl pyrophosphate analogue is an inhibitor of FTase, while the corresponding alcohol is not. These results, together with Western blot analyses of cell lysates, indicate that the farnesyl pyrophosphate analogue penetrates the cells as an intact pyrophosphate and that it does so at a biologically relevant concentration.

A tagging-via-substrate technology for detection and proteomics of farnesylated proteins

A recently developed proteomics strategy, designated tagging-via-substrate (TAS) approach, is described for the detection and proteomic analysis of farnesylated proteins. TAS technology involves metabolic incorporation of a synthetic azido-farnesyl analog and chemoselective derivatization of azido-farnesyl-modified proteins by an elegant version of Staudinger reaction, pioneered by the Bertozzi group, using a biotinylated phosphine capture reagent. The resulting protein conjugates can be specifically detected and/or affinity-purified by streptavidin-linked horseradish peroxidase or agarose beads, respectively. Thus, the technology enables global profiling of farnesylated proteins by enriching farnesylated proteins and reducing the complexity of farnesylation subproteome. Azido-farnesylated proteins maintain the properties of protein farnesylation, including promoting membrane association, Ras-dependent mitogen-activated protein kinase kinase activation, and inhibition of lovastatin-induced apoptosis. A proteomic analysis of farnesylated proteins by TAS technology revealed 18 farnesylated proteins, including those with potentially novel farnesylation motifs, suggesting that future use of this method is likely to yield novel insight into protein farnesylation. TAS technology can be extended to other posttranslational modifications, such as geranylgeranylation and myristoylation, thus providing powerful tools for detection, quantification, and proteomic analysis of posttranslationally modified proteins.

Molecular Cloning and Characterization of a Protein Farnesyltransferase from the Enteric Protozoan Parasite Entamoeba histolytica

Genes encoding alpha- and beta-subunits of a putative protein farnesyltransferase (FT) from the enteric protozoan parasite Entamoeba histolytica were obtained and their biochemical properties were characterized. Deduced amino acid sequences of the alpha- and beta-subunit of E. histolytica FT (EhFT) were 298- and 375-residues long with a molecular mass of 35.6 and 42.6 kDa, and a pI of 5.43 and 5.65, respectively. They showed 24% to 36% identity to and shared common signature domains and repeats with those from other organisms. Recombinant alpha- and beta-subunits, co-expressed in Escherichia coli, formed a heterodimer and showed activity to transfer farnesyl using farnesylpyrophosphate as a donor to human H-Ras possessing a C-terminal CVLS, but not a mutant H-Ras possessing CVLL. Among a number of small GTPases that belong to the Ras superfamily from this parasite, we identified EhRas4, which possesses CVVA at the C terminus, as a sole farnesyl acceptor for EhFT. This is in contrast to mammalian FT, which utilizes a variety of small GTPases that possess a C-terminal CaaX motif, where X is serine, methionine, glutamine, cysteine, or alanine. EhFT also showed remarkable resistance against a variety of known inhibitors of mammalian FT. These results suggest that remarkable biochemical differences in binding to substrates and inhibitors exist between amebic and mammalian FTs, which highlights this enzyme as a novel target for the development of new chemotherapeutics against amebiasis.

Synthesis of 7-substituted farnesyl diphosphate analogues

[structure: see text] Six farnesyl diphosphate analogues modified in the central isoprene unit have been prepared via our stereoselective vinyl triflate-mediated route to isoprenoids. The 7-allyl compound 6 is a modest inhibitor of mammalian protein-farnesyl transferase, but surprisingly the other five analogues are effective alternative substrates for this enzyme.

Photoaffinity analogues of farnesyl pyrophosphate transferable by protein farnesyl transferase

Farnesylation is a posttranslational lipid modification in which a 15-carbon farnesyl isoprenoid is linked via a thioether bond to specific cysteine residues of proteins in a reaction catalyzed by protein farnesyltransferase (FTase). We synthesized analogues (3-6) of farnesyl pyrophosphate (FPP) to probe the range of modifications possible to the FPP skeleton which allow for efficient transfer by FTase. Photoaffinity analogues of FPP (5, 6) were prepared by substituting perfluorophenyl azide functional groups for the omega-terminal isoprene of FPP. Substituted anilines replace the omega-terminal isoprene in analogues 3 and 4. Compounds 3-5 were prepared by reductive amination of the appropriate anilines with 8-oxo-geranyl acetate, followed by ester hydrolysis, chlorination, and pyrophosphorylation. Additional substitution of three methylenes for the beta-isoprene of FPP gave photoprobe 6 in nine steps. Preparation of the analogues required TiCl(4)-mediated imine formation prior to NaBH(OAc)(3) reduction for anilines with a pK(a) < 1. The azide moiety was not affected by Ph(3)PCl(2) conversion of allylic alcohols 13-16 into corresponding chlorides 17-20. Analogues 3-6 are efficiently transferred to target N-dansyl-GCVLS peptide substrate by mammalian FTase. Comparison of analogue structures and kinetics of transfer to those of FPP reveals that ring fluorination and para substituents have little effect on the affinity of the analogue pyrophosphate for FTase and its transfer efficiency. These results are also supported with models of the analogue binding modes in the active site of FTase. The transferable azide photoprobe 5 photoinactivates FTase. Transferable analogues 5 and 6 allow the formation of appropriately posttranslationally modified photoreactive peptide probes of isoprene function.

Aromatic farnesyl diphosphate analogues: vinyl triflate-mediated synthesis and preliminary enzymatic evaluation

A stereocontrolled vinyl triflate-based synthetic route has been used to prepare four analogues of farnesyl diphosphate (FPP) where the terminal isoprene units have been replaced with aromatic moieties. Two of these analogues exhibit no productive interaction with protein farnesyltransferase, but the 2-naphthyl derivative 2 is a modest inhibitor of the enzyme, and the para-biphenyl derivative 4 is a surprisingly effective alternative substrate.