Prenyl Lipid Research Articles

Use of Biotin-Labeled Geranyl Pyrophosphate for Analysis of Ykt6 Geranylgeranylation.

Functionally derivatized analogs of prenyl lipids are valuable tools for the detection and analysis of prenylated proteins. Using a biotinylated analog of geranylgeranyl, we previously identified Ykt6 as a substrate for a novel protein prenyltransferase, termed geranylgeranyltransferase type III (GGTase-III). Ykt6 is an evolutionarily highly conserved SNARE protein that regulates multiple intracellular trafficking pathways, including intra-Golgi trafficking and autophagosome-lysosome fusion. Unlike most SNARE proteins, which are membrane-anchored via a C-terminal transmembrane region, Ykt6 is uniquely attached to the membrane by lipid modifications at two conserved cysteines near the C-terminus (Cys194 and Cys195 in human Ykt6). Cys195, the fourth residue from the C-terminus, is farnesylated by farnesyltransferase (FTase), while Cys194 is geranylgeranylated by GGTase-III. These two enzymes sequentially transfer farnesyl and geranylgeranyl groups to Ykt6, producing a doubly prenylated form of Ykt6. Double prenylation is essential for the function of Ykt6 and is crucial for the maintenance of the Golgi apparatus and autophagosome clearance. Here we describe the use of the biotin-labeled geranylgeranyl analog to identify Ykt6 as a GGTase-III substrate.

Chromoplast plastoglobules recruit the carotenoid biosynthetic pathway and contribute to carotenoid accumulation during tomato fruit maturation.

Tomato (Solanum lycopersicum) fruit maturation is associated with a developmental transition from chloroplasts (in mature green fruit) to chromoplasts (in red fruit). The hallmark red color of ripe tomatoes is due to carotenogenesis and accumulation of the red carotenoid lycopene inside chromoplasts. Plastoglobules (PG) are lipid droplets in plastids that are involved in diverse lipid metabolic pathways. In tomato, information on the possible role of PG in carotogenesis and the PG proteome is largely lacking. Here, we outline the role of PG in carotenogenesis giving particular attention to tomato fruit PG proteomes and metabolomes. The proteome analysis revealed the presence of PG-typical FBNs, ABC1K-like kinases, and metabolic enzymes, and those were decreased in the PG of tomato chromoplasts compared to chloroplasts. Notably, the complete β-carotene biosynthesis pathway was recruited to chromoplast PG, and the enzymes PHYTOENE SYNTHASE 1 (PSY-1), PHYTOENE DESATURASE (PDS), ZETA-CAROTENE DESATURASE (ZDS), and CAROTENOID ISOMERASE (CRTISO) were enriched up to twelvefold compared to chloroplast PG. We profiled the carotenoid and prenyl lipid changes in PG during the chloroplast to chromoplast transition and demonstrated large increases of lycopene and β-carotene in chromoplast PG. The PG proteome and metabolome are subject to extensive remodeling resulting in high accumulation of lycopene during the chloroplast-to-chromoplast transition. Overall, the results indicate that PGs contribute to carotenoid accumulation during tomato fruit maturation and suggest that they do so by functioning as a biosynthetic platform for carotenogenesis.

Improving the co-production of triacylglycerol and isoprenoids in Chlamydomonas

Biodiesel and natural products derived from microalgae require a smaller land area and have higher production rates compared to plants and animals and has recently attracted considerable interest. However, biodiesel production from microalgal triacylglycerol is still far from commercial realization due to its high production cost. One way to overcome this obstacle is to improve the triacylglycerol accumulation and couple its production with other high-value compounds. Of particular interest is the sterol biosynthetic pathway with squalene as an intermediate due to its close relationship with triacylglycerol and carotenoid biosynthetic pathways. Besides, both squalene and carotenoids are isoprenoid lipids that have health benefits. Perturbation of one pathway has been suggested to affect other pathways. Three terbinafine-sensitive mutants of the green microalga Chlamydomonas reinhardtii were isolated using terbinafine, a drug that inhibits squalene epoxidase, leading to squalene accumulation. One of the mutants, tfs2, accumulated twice the amount of wild-type triacylglycerol. As well as squalene accumulation, the presence of terbinafine further increased the triacylglycerol content. The level of prenyl lipid carotenoid and chlorophyll was also more significant than that of the wild type. Growth and photosynthesis were not compromised in this mutant. This is the first study that has demonstrated a mutant screening method to improve the co-production of TAG and isoprenoid lipids in a green microalgae.

Molecular Logic of Prokaryotic Surface Layer Structures.

Most prokaryotic cells are encased in a surface layer (S-layer) consisting of a paracrystalline array of repeating lattice-forming proteins. S-layer proteins populate a vast and diverse sequence space, performing disparate functions in prokaryotic cells, including cellular defense, cell-shape maintenance, and regulation of import and export of materials. This article highlights recent advances in the understanding of S-layer structure and assembly, made possible by rapidly evolving structural and cell biology methods. We underscore shared assembly principles revealed by recent work and discuss a common molecular framework that may be used to understand the structural organization of S-layer proteins across bacteria and archaea.

Metabolic shifts associated with drought-induced senescence in Brachypodium

The metabolic underpinnings of plant survival under severe drought-induced senescence conditions are poorly understood. In this study, we assessed the morphological, physiological and metabolic responses to sustained water deficit in Brachypodium distachyon, a model organism for research on temperate grasses. Relative to control plants, fresh biomass, leaf water potential, and chlorophyll levels decreased rapidly in plants grown under drought conditions, demonstrating an early onset of senescence. The leaf C/N ratio and protein content showed an increase in plants subjected to drought stress. The concentrations of several small molecule carbohydrates and amino acid-derived metabolites previously implicated in osmotic protection increased rapidly in plants experiencing water deficit. Malic acid, a low molecular weight organic acid with demonstrated roles in stomatal closure, also increased rapidly as a response to drought treatment. The concentrations of prenyl lipids, such as phytol and α-tocopherol, increased early during the drought treatment but then dropped dramatically. Surprisingly, continued changes in the quantities of metabolites were observed, even in samples harvested from visibly senesced plants. The data presented here provide insights into the processes underlying persistent metabolic activity during sustained water deficit and can aid in identifying mechanisms of drought tolerance in plants.

A novel prenyl-polybasic domain code determines lipid-binding specificity of the K-Ras membrane anchor

ABSTRACTRas proteins must localize to the plasma membrane (PM) for biological function. The membrane anchor of the K-Ras4B isoform comprises a farnesylated and methylated C-terminal cysteine together with an adjacent hexa-lysine polybasic domain (PBD). Traditionally, polybasic sequences have been thought to interact electrostatically with negatively charged membranes showing no specificity for anionic lipid head groups. By contrast we recently showed that the K-Ras membrane anchor actually exhibits a very high degree of specificity for phosphatidylserine (PtdSer). The selectivity for PtdSer is determined by a combinatorial code comprising the PBD sequence plus the prenyl anchor. Lipid binding specificity is therefore altered by PBD point mutations that in turn modulate signaling output. For example, mutating Lys177 or Lys178 to glutamine switches K-Ras4B lipid affinity from PtdSer to phosphoinositol 4,5-bisphosphate (PIP2). Changing the lipid anchor from farnesyl to geranylgeranyl or the PBD lysines to arginines also changes lipid binding specificity. All-atom molecular dynamics simulations reveal the structural basis for these K-Ras anchor lipid-binding preferences. Here we examine the PM interactions of a series of geranylgeranylated PBD mutants and provide further evidence that the precise PBD sequence and prenyl lipid determines lipid sorting specificity of the K-Ras anchor and hence biological function.

Atomic structure of the eukaryotic intramembrane RAS methyltransferase ICMT.

The maturation of Ras GTPases, and ~200 other cellular CaaX proteins, involves three enzymatic steps: addition of a farnesyl or geranylgeranyl prenyl lipid to the cysteine (C) in the C-terminal CaaX motif, proteolytic cleavage of the aaX residues, and methylation of the exposed prenylcysteine residue at its terminal carboxylate1. This final step is catalyzed by isoprenylcysteine carboxyl methyltransferase (ICMT), a eukaryotic-specific integral membrane enzyme of the endoplasmic reticulum (ER)2. ICMT is the only cellular enzyme known to methylate prenylcysteine substrates; methylation is important for their biological functions, including the membrane localisations and subsequent activities of Ras1, prelamin A3, and Rab4. ICMT inhibition has potential for combating progeria3 and cancer5–8. Here we present an X-ray structure of ICMT, at 2.3 Å resolution, in complex with its cofactor, an ordered lipid molecule and a monobody inhibitor. The active site spans cytosolic and membrane-exposed regions, indicating distinct entry routes for its cytosolic methyl donor, S-adenosyl-L-methionine (AdoMet), and for prenylcysteine substrates, which are associated with the ER membrane. The structure suggests how ICMT overcomes the topographical challenge and unfavourable energetics of bringing two reactants that have different cellular localisations together in a membrane environment – a relatively uncharacterized, but defining feature of many integral membrane enzymes.

Unique structural features of the AIPL1–FKBP domain that support prenyl lipid binding and underlie protein malfunction in blindness

FKBP-domain proteins (FKBPs) are pivotal modulators of cellular signaling, protein folding, and gene transcription. Aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) is a distinctive member of the FKBP superfamily in terms of its biochemical properties, and it plays an important biological role as a chaperone of phosphodiesterase 6 (PDE6), an effector enzyme of the visual transduction cascade. Malfunction of mutant AIPL1 proteins triggers a severe form of Leber congenital amaurosis and leads to blindness. The mechanism underlying the chaperone activity of AIPL1 is largely unknown, but involves the binding of isoprenyl groups on PDE6 to the FKBP domain of AIPL1. We solved the crystal structures of the AIPL1-FKBP domain and its pathogenic mutant V71F, both in the apo form and in complex with isoprenyl moieties. These structures reveal a module for lipid binding that is unparalleled within the FKBP superfamily. The prenyl binding is enabled by a unique "loop-out" conformation of the β4-α1 loop and a conformational "flip-out" switch of the key W72 residue. A second major conformation of apo AIPL1-FKBP was identified by NMR studies. This conformation, wherein W72 flips into the ligand-binding pocket and renders the protein incapable of prenyl binding, is supported by molecular dynamics simulations and appears to underlie the pathogenicity of the V71F mutant. Our findings offer critical insights into the mechanisms that underlie AIPL1 function in health and disease, and highlight the structural and functional diversity of the FKBPs.

Quantitative and qualitative characteristics of cell wall components and prenyl lipids in the leaves of Tilia x euchlora trees growing under salt stress.

The study was focused on assessing the presence of arabinogalactan proteins (AGPs) and pectins within the cell walls as well as prenyl lipids, sodium and chlorine content in leaves of Tilia x euchlora trees. The leaves that were analyzed were collected from trees with and without signs of damage that were all growing in the same salt stress conditions. The reason for undertaking these investigations was the observations over many years that indicated that there are trees that present a healthy appearance and trees that have visible symptoms of decay in the same habitat. Leaf samples were collected from trees growing in the median strip between roadways that have been intensively salted during the winter season for many years. The sodium content was determined using atomic spectrophotometry, chloride using potentiometric titration and poly-isoprenoids using HPLC/UV. AGPs and pectins were determined using immunohistochemistry methods. The immunohistochemical analysis showed that rhamnogalacturonans I (RG-I) and homogalacturonans were differentially distributed in leaves from healthy trees in contrast to leaves from injured trees. In the case of AGPs, the most visible difference was the presence of the JIM16 epitope. Chemical analyses of sodium and chloride showed that in the leaves from injured trees, the level of these ions was higher than in the leaves from healthy trees. Based on chromatographic analysis, four poly-isoprenoid alcohols were identified in the leaves of T. x euchlora. The levels of these lipids were higher in the leaves from healthy trees. The results suggest that the differences that were detected in the apoplast and symplasm may be part of the defensive strategy of T. x euchlora trees to salt stress, which rely on changes in the chemical composition of the cell wall with respect to the pectic and AGP epitopes and an increased synthesis of prenyl lipids.

Plastoglobuli: Plastid Microcompartments with Integrated Functions in Metabolism, Plastid Developmental Transitions, and Environmental Adaptation.

Plastoglobuli (PGs) are plastid lipoprotein particles surrounded by a membrane lipid monolayer. PGs contain small specialized proteomes and metabolomes. They are present in different plastid types (e.g., chloroplasts, chromoplasts, and elaioplasts) and are dynamic in size and shape in response to abiotic stress or developmental transitions. PGs in chromoplasts are highly enriched in carotenoid esters and enzymes involved in carotenoid metabolism. PGs in chloroplasts are associated with thylakoids and contain ∼30 core proteins (including six ABC1 kinases) as well as additional proteins recruited under specific conditions. Systems analysis has suggested that chloroplast PGs function in metabolism of prenyl lipids (e.g., tocopherols, plastoquinone, and phylloquinone); redox and photosynthetic regulation; plastid biogenesis; and senescence, including recycling of phytol, remobilization of thylakoid lipids, and metabolism of jasmonate. These functionalities contribute to chloroplast PGs' role in responses to stresses such as high light and nitrogen starvation. PGs are thus lipid microcompartments with multiple functions integrated into plastid metabolism, developmental transitions, and environmental adaptation. This review provides an in-depth overview of PG experimental observations, summarizes the present understanding of PG features and functions, and provides a conceptual framework for PG research and the realization of opportunities for crop improvement.

Plastoglobules in algae: A comprehensive comparative study of the presence of major structural and functional components in complex plastids

Plastoglobules (PG) are lipophilic droplets attached to thylakoid membranes in higher plants and green algae and are implicated in prenyl lipid biosynthesis. They might also represent a central hub for integration of plastid signals under stress and therefore the adaptation of the thylakoid membrane under such conditions. In Arabidopsis thaliana, PG contain around 30 specific proteins of which Fibrillins (FBN) and Activity of bc1 complex kinases (ABC1K) represent the majority with respect to both number and protein mass. However, nothing is known about the presence of PG in most algal species, which are responsible for about 50% of global primary production. Therefore, we searched the genomes of publicly available algal genomes for components of PG and the associated functional network in order to predict their presence and potential evolutionary conservation of physiological functions. We could identify homologous sequences for core components of PG, like FBN and ABC1K, in most investigated algal species. Furthermore, proteins at central and interesting positions within the PG functional coexpression network were identified. Phylogenetic sequence analysis revealed diversity within FBN and ABC1K sequences among algal species with complex plastids of the red lineage and large differences compared with green lineage species. Two types of FBN were detected that differ in their isoelectric point which seems to correlate with subcellular localization. Subgroups of FBN were shared between many investigated species and modeling of their 3D-structure implied a conserved structure. FBN and ABC1K are essential structural and functional components of PG. Their occurrence in investigated algal species suggests presence of PG therein and functions in prenyl lipid metabolism and adaptation of the thylakoid membrane that are conserved during evolution.

Permuting the PGF Signature Motif Blocks both Archaeosortase-Dependent C-Terminal Cleavage and Prenyl Lipid Attachment for the Haloferax volcanii S-Layer Glycoprotein.

For years, the S-layer glycoprotein (SLG), the sole component of many archaeal cell walls, was thought to be anchored to the cell surface by a C-terminal transmembrane segment. Recently, however, we demonstrated that the Haloferax volcanii SLG C terminus is removed by an archaeosortase (ArtA), a novel peptidase. SLG, which was previously shown to be lipid modified, contains a C-terminal tripartite structure, including a highly conserved proline-glycine-phenylalanine (PGF) motif. Here, we demonstrate that ArtA does not process an SLG variant where the PGF motif is replaced with a PFG motif (slg(G796F,F797G)). Furthermore, using radiolabeling, we show that SLG lipid modification requires the PGF motif and is ArtA dependent, lending confirmation to the use of a novel C-terminal lipid-mediated protein-anchoring mechanism by prokaryotes. Similar to the case for the ΔartA strain, the growth, cellular morphology, and cell wall of the slg(G796F,F797G) strain, in which modifications of additional H. volcanii ArtA substrates should not be altered, are adversely affected, demonstrating the importance of these posttranslational SLG modifications. Our data suggest that ArtA is either directly or indirectly involved in a novel proteolysis-coupled, covalent lipid-mediated anchoring mechanism. Given that archaeosortase homologs are encoded by a broad range of prokaryotes, it is likely that this anchoring mechanism is widely conserved. Prokaryotic proteins bound to cell surfaces through intercalation, covalent attachment, or protein-protein interactions play critical roles in essential cellular processes. Unfortunately, the molecular mechanisms that anchor proteins to archaeal cell surfaces remain poorly characterized. Here, using the archaeon H. volcanii as a model system, we report the first in vivo studies of a novel protein-anchoring pathway involving lipid modification of a peptidase-processed C terminus. Our findings not only yield important insights into poorly understood aspects of archaeal biology but also have important implications for key bacterial species, including those of the human microbiome. Additionally, insights may facilitate industrial applications, given that photosynthetic cyanobacteria encode uncharacterized homologs of this evolutionarily conserved enzyme, or may spur development of unique drug delivery systems.

13C-isotope-based protocol for prenyl lipid metabolic analysis in zebrafish embryos

Metabolism has a decisive role in many fundamental biological processes, including organism development and tissue homeostasis. Here we describe a protocol for fast and reliable (13)C-isotope-based in vivo metabolic profiling. This protocol covers the loading of isotope precursor; extraction, preparation and quantification of the labeled lipid metabolites (e.g., the prenyl lipid CoQ10) by the means of HPLC-MS; and its analysis in zebrafish embryos. This protocol can be applied to different types of experimental settings, including tissue-specific metabolic analyses or dynamic metabolic changes that occur during vertebrate embryogenesis. The protocol takes 5-7 d to complete, requiring minimal equipment and analytical expertise, and it represents a unique alternative to the existing ex vivo (e.g., cell lines) isotope-based metabolic methods. This procedure represents a valuable approach for researchers interested in studying the effect of gene manipulation on lipid metabolism in zebrafish and in understanding the genetic conditions that result in metabolism dysfunction.

Mechanism of Isoprenylcysteine Carboxyl Methylation from the Crystal Structure of the Integral Membrane Methyltransferase ICMT

The posttranslational modification of C-terminal CAAX motifs in proteins such as Ras, most Rho GTPases, and G protein γ subunits, plays an essential role in determining their subcellular localization and correct biological function. An integral membrane methyltransferase, isoprenylcysteine carboxyl methyltransferase (ICMT), catalyzes the final step of CAAX processing after prenylation of the cysteine residue and endoproteolysis of the -AAX motif. We have determined the crystal structure of a prokaryotic ICMT ortholog, revealing a markedly different architecture from conventional methyltransferases that utilize S-adenosyl-L-methionine (SAM) as a cofactor. ICMT comprises a core of five transmembrane α helices and a cofactor-binding pocket enclosed within a highly conserved C-terminal catalytic subdomain. A tunnel linking the reactive methyl group of SAM to the inner membrane provides access for the prenyl lipid substrate. This study explains how an integral membrane methyltransferase achieves recognition of both a hydrophilic cofactor and a lipophilic prenyl group attached to a polar protein substrate.

Abstract B26: Roles of NgBR in promoting Ras translocation and Ras signaling in human breast cancer cells

Abstract NgBR is a type I receptor with a single transmembrane domain. Our previous work has shown that axon guidance gene family Nogo-B and its receptor (NgBR) are essential for chemotaxis and morphogenesis of endothelial cells in vitro and blood vessel formation in Zebrafish. Here, we demonstrate that NgBR binds and translocates farnesylated Ras to plasma membranes, which results in the activation of PI3K-Akt and Raf-MEK-ERK signaling pathways in human breast cancer cells. Comparing NgBR to other sequences in the NCBI database reveals that regions of the cytoplasmic domain have a high degree of similarity (49%) to the cis-lsoprenyl Disphosphate Synthases (cis-IPPS) family of lipid modifying enzymes. However, NgBR lacks key residues required for catalytic activity, but contains a conserved hydrophobic tunnel for shuttling prenyl lipids and/or prenylated proteins. Farnesylation of Ras is essential for Ras translocation and activation. Direct interaction between NgBR and farnesylated Ras has been demonstrated by co-immunoprecipitation of MBP-NgBR from incubation of purified recombinant MBP-NgBR and farnesylated Ras protein. Knockdown of NgBR in MDA-MB-231 human breast cancer cells remarkably reduces the amount of membrane-associated Ras. These results suggest that NgBR is a potential modulator for Ras translocation. Immunohistochemistry analysis of human breast tumor tissue arrays revealed that NgBR is highly expressed in human breast cancer tissues. We further used real-time PCR to determine the copy number of NgBR transcripts in human breast tumor tissues. Accompanying pathology reports were used to categorize the 84 breast tumor tissues into four different grades from I to IV. Real-time PCR results show that NgBR expression is significantly higher in Grade II and Grade III-IV breast tumors when compared with normal breast samples (12 samples) and Grade I breast tumor samples (21 samples). 62% of Grade II (34 samples) and 55% of Grade III-IV (29 samples) breast tumors had increased NgBR transcripts (>50% higher) when compared with normal breast tissues. These data suggest that NgBR expression is strongly associated with advanced breast cancers. Interestingly, NgBR is highly expressed in several breast cancer cells such as MDA-MB-231 cells as compared to immortalized mammary epithelial cells MCF-10A. Knockdown of NgBR expression in MDA-MB-231 breast cancer cells decreases cancer cell colony formation, and abolishes EGF-stimulated Ras activation and phosphorylation of Akt in MDA-MB-231 cells. In addition, overexpression of NgBR caused the transformation of NIH-3T3 cells via enhancing Ras plasma membrane translocation and EGF-stimulated Ras signaling. Consequently, our preliminary results further demonstrated that inducible knockdown of NgBR in tumor xenograft of MDA-MB-231 cells in nude mice significantly retards tumor growth. Thus, these data demonstrate that NgBR is a unique receptor that recruits farnesylated Ras to the plasma membrane via its hydrophobic cytoplasmic domain and then activates both PI3K-Akt and Raf-MEK-ERK pathways in human breast cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B26.

Lipid Diffusion In Domain-forming Bilayers Studied By Pfg-nmr

The pulsed field gradient (pfg)-NMR method for measurements of translational diffusion of molecules in aligned lipid bilayers is presented. Lateral phase separation of lipids has been successfully studied as well as their dynamics within the bilayer organization. Support was obtained for that the lateral diffusion depends on lipid packing and acyl chain ordering. Therefore, investigations of order parameters of perdeuterated acyl chains, using 2H NMR quadrupole splittings, were useful complements. Here, some of our recent achievements on lipid membranes will be summarized. In particular, bilayers exhibiting two-phase coexistence of liquid disordered (ld) and liquid ordered (lo) phases are considered in detail. Among our major results are that the lateral diffusion is the same for all components, independent of the molecular structure (including cholesterol (CHOL)), if they reside in the same domain in the membrane. Furthermore, quite unexpectedly CHOL seems to partition into the ld and lo phases to roughly the same extent, indicating that CHOL has no strong preference for any of these phases. We propose that the lateral phase separation in bilayers containing one high Tm and one low Tm lipid together with CHOL is driven by the increasing difficulty of incorporating an unsaturated or prenyl lipid into the highly ordered bilayer formed by a saturated lipid and CHOL, i.e. the phase transition is entropy driven to keep the disorder of the hydrocarbon chains of the unsaturated lipid.

A Salvage Pathway for Phytol Metabolism in Arabidopsis

Chlorophyll is the most abundant photosynthetic pigment in higher plants. During senescence, chlorophyll is hydrolyzed, resulting in the release of free phytol and chlorophyllide. Although the degradation of chlorophyllide has been studied in depth, the metabolic fate of phytol in plants is less clear. Here, we provide evidence that phytol can be incorporated into chlorophyll, tocopherol, and lipid esters by Arabidopsis seedlings. Phytol is phosphorylated to phytyl-phosphate and phytyl-diphosphate by two successive kinase activities associated with chloroplast envelope membranes of Arabidopsis. Although phytol kinase is CTP-dependent, the second kinase reaction, phytyl-phosphate kinase, shows broader specificity for CTP, GTP, UTP, and ATP. Therefore, in addition to de novo synthesis from geranylgeranyl-diphosphate, phosphorylation of free phytol represents an alternative route for phytyl-diphosphate production as the precursor for chloroplast prenyl lipid synthesis. Lipid esters are produced after feeding phytol to Arabidopsis seedlings, and they also accumulate in large amounts in leaves during senescence. The predominant phytyl ester that accumulates during senescence is hexadecatrienoic acid phytyl ester. Fatty acid phytyl ester synthesis by protein extracts of Arabidopsis is stimulated in the presence of phytol- and acyl-CoA esters. Thus, Arabidopsis contains a distinct enzymatic machinery for redirecting free phytol released from chlorophyll degradation into chloroplast lipid metabolism.

Therapy for HDV!

Hepatitis delta virus (HDV) can dramatically worsen liver disease in patients coinfected with hepatitis B virus (HBV). No effective medical therapy exists for HDV. The HDV envelope requires HBV surface antigen proteins provided by HBV. Once inside a cell, however, HDV can replicate its genome in the absence of any HBV gene products. In vitro, HDV virion assembly is critically dependent on prenyl lipid modification, or prenylation, of its nucleocapsid–like protein large delta antigen. To overcome limitations of current animal models and to test the hypothesis that pharmacologic prenylation inhibition can prevent the production of HDV virions in vivo, we established a convenient mouse–based model of HDV infection capable of yielding viremia. Such mice were then treated with the prenylation inhibitors FTI–277 and FTI–2153. Both agents were highly effective at clearing HDV viremia. As expected, HDV inhibition exhibited duration–of–treatment dependence. These results provide the first preclinical data supporting the in vivo efficacy of prenylation inhibition as a novel antiviral therapy with potential application to HDV and a wide variety of other viruses.

In vivo antiviral efficacy of prenylation inhibitors against hepatitis delta virus.

Hepatitis delta virus (HDV) can dramatically worsen liver disease in patients coinfected with hepatitis B virus (HBV). No effective medical therapy exists for HDV. The HDV envelope requires HBV surface antigen proteins provided by HBV. Once inside a cell, however, HDV can replicate its genome in the absence of any HBV gene products. In vitro, HDV virion assembly is critically dependent on prenyl lipid modification, or prenylation, of its nucleocapsid-like protein large delta antigen. To overcome limitations of current animal models and to test the hypothesis that pharmacologic prenylation inhibition can prevent the production of HDV virions in vivo, we established a convenient mouse-based model of HDV infection capable of yielding viremia. Such mice were then treated with the prenylation inhibitors FTI-277 and FTI-2153. Both agents were highly effective at clearing HDV viremia. As expected, HDV inhibition exhibited duration-of-treatment dependence. These results provide the first preclinical data supporting the in vivo efficacy of prenylation inhibition as a novel antiviral therapy with potential application to HDV and a wide variety of other viruses.

Protein prenyltransferases.

Three different protein prenyltransferases catalyze the attachment of prenyl lipid anchors to a variety of eukaryotic proteins. Farnesyltransferase-inhibitor drugs have been developed as anti-cancer agents and may also be able to treat several other diseases.