The plurality of long chain isoprenoid alcohols (polyprenols) from natural sources

The Essential Role of Cholesterol Metabolism in the Intracellular Survival of Mycobacterium leprae Is Not Coupled to Central Carbon Metabolism and Energy Production

Mycobacterium leprae induces the formation of lipid droplets, which are recruited to pathogen-containing phagosomes in infected macrophages and Schwann cells. Cholesterol is among the lipids with increased abundance in M. leprae-infected cells, and intracellular survival relies on cholesterol accumulation. The present study investigated the capacity of M. leprae to acquire and metabolize cholesterol. In silico analyses showed that oxidation of cholesterol to cholest-4-en-3-one (cholestenone), the first step of cholesterol degradation catalyzed by the enzyme 3β-hydroxysteroid dehydrogenase (3β-HSD), is apparently the only portion of the cholesterol catabolic pathway seen in Mycobacterium tuberculosis preserved by M. leprae. Incubation of bacteria with radiolabeled cholesterol confirmed the in silico predictions. Radiorespirometry and lipid analyses performed after incubating M. leprae with [4-¹⁴C]cholesterol or [26-¹⁴C]cholesterol showed the inability of this pathogen to metabolize the sterol rings or the side chain of cholesterol as a source of energy and carbon. However, the bacteria avidly incorporated cholesterol and, as expected, converted it to cholestenone both in vitro and in vivo. Our data indicate that M. leprae has lost the capacity to degrade and utilize cholesterol as a nutritional source but retains the enzyme responsible for its oxidation to cholestenone. Thus, the essential role of cholesterol metabolism in the intracellular survival of M. leprae is uncoupled from central carbon metabolism and energy production. Further elucidation of cholesterol metabolism in the host cell during M. leprae infection will establish the mechanism by which this lipid supports M. leprae intracellular survival and will open new avenues for novel leprosy therapies.

IMPORTANCE Our study focused on the obligate intracellular pathogen Mycobacterium leprae and its capacity to metabolize cholesterol. The data make an important contribution for those interested in understanding the mechanisms of mycobacterial pathogenesis, since they indicate that the essential role of cholesterol for M. leprae intracellular survival does not rely on its utilization as a nutritional source. Our findings reinforce the complexity of cholesterol's role in sustaining M. leprae infection. Further elucidation of cholesterol metabolism in the host cell during M. leprae infection will establish the mechanism by which this lipid supports M. leprae intracellular survival and will open new avenues for novel leprosy therapies.

Novel Citronellyl-Based Photoprobes Designed to Identify ER Proteins Interacting with Dolichyl Phosphate in Yeast and Mammalian Cells

BACKGROUND

Dolichyl phosphate-linked mono- and oligosaccharides (DLO) are essential intermediates in protein N-glycosylation, C- and O-mannosylation and GPI anchor biosynthesis. While many membrane proteins in the endoplasmic reticulum (ER) involved in the assembly of DLOs are known, essential proteins believed to be required for the transbilayer movement (flip-flopping) and proteins potentially involved in the regulation of DLO synthesis remain to be identified.

METHODS

The synthesis of a series of Dol-P derivatives composed of citronellyl-based photoprobes with benzophenone groups equipped with alkyne moieties for Huisgen "click" chemistry is now described to utilize as tools for identifying ER proteins involved in regulating the biosynthesis and transbilayer movement of lipid intermediates. In vitro enzymatic assays were used to establish that the photoprobes contain the critical structural features recognized by pertinent enzymes in the dolichol pathway. ER proteins that photoreacted with the novel probes were identified by MS.

RESULTS

The potential of the newly designed photoprobes, m-PAL-Cit-P and p-PAL-Cit-P, for identifying previously unidentified Dol-P-interacting proteins is supported by the observation that they are enzymatically mannosylated by Man-P-Dol synthase (MPDS) from Chinese Hamster Ovary (CHO) cells at an enzymatic rate similar to that for Dol-P. MS analyses reveal that DPM1, ALG14 and several other yeast ER proteins involved in DLO biosynthesis and lipid-mediated protein O-mannosylation photoreacted with the novel probes.

CONCLUSION

The newly-designed photoprobes described in this paper provide promising new tools for the identification of yet to be identified Dol-P interacting ER proteins in yeast and mammalian cells, including the Dol-P flippase required for the "re-cycling" of the glycosyl carrier lipid from the lumenal monolayer of the ER to the cytoplasmic leaflet for new rounds of DLO synthesis.

A novel epimerase that converts GlcNAc-P-P-undecaprenol to GalNAc-P-P-undecaprenol in Escherichia coli O157

Escherichia coli strain O157 produces an O-antigen with the repeating tetrasaccharide unit alpha-D-PerNAc-alpha-l-Fuc-beta-D-Glc-alpha-D-GalNAc, preassembled on undecaprenyl pyrophosphate (Und-P-P). These studies were conducted to determine whether the biosynthesis of the lipid-linked repeating tetrasaccharide was initiated by the formation of GalNAc-P-P-Und by WecA. When membrane fractions from E. coli strains K12, O157, and PR4019, a WecA-overexpressing strain, were incubated with UDP-[3H]GalNAc, neither the enzymatic synthesis of [3H]GlcNAc-P-P-Und nor [3H]GalNAc-P-P-Und was detected. However, when membrane fractions from strain O157 were incubated with UDP-[3H]GlcNAc, two enzymatically labeled products were observed with the chemical and chromatographic properties of [3H]GlcNAc-P-P-Und and [3H]GalNAc-P-P-Und, suggesting that strain O157 contained an epimerase capable of interconverting GlcNAc-P-P-Und and GalNAc-P-P-Und. The presence of a novel epimerase was demonstrated by showing that exogenous [3H]GlcNAc-P-P-Und was converted to [3H]GalNAc-P-P-Und when incubated with membranes from strain O157. When strain O157 was metabolically labeled with [3H]GlcNAc, both [3H]GlcNAc-P-P-Und and [3H]GalNAc-P-P-Und were detected. Transformation of E. coli strain 21546 with the Z3206 gene enabled these cells to synthesize GalNAc-P-P-Und in vivo and in vitro. The reversibility of the epimerase reaction was demonstrated by showing that [3H]GlcNAc-P-P-Und was reformed when membranes from strain O157 were incubated with exogenous [3H]GalNAc-P-P-Und. The inability of Z3206 to complement the loss of the gne gene in the expression of the Campylobacter jejuni N-glycosylation system in E. coli indicated that it does not function as a UDP-GlcNAc/UDP-GalNAc epimerase. Based on these results, GalNAc-P-P-Und is synthesized reversibly by a novel GlcNAc-P-P-Und epimerase after the formation of GlcNAc-P-P-Und by WecA in E. coli O157.

The structural basis of chain length control in Rv1086

In Mycobacterium tuberculosis, two related Z-prenyl diphosphate synthases, E,Z-farnesyl diphosphate synthase (Rv1086) and decaprenyl diphosphate synthase (Rv2361c), work in series to synthesize decaprenyl phosphate (C(50)) from isopentenyl diphosphate and E-geranyl diphosphate. Decaprenyl phosphate plays a central role in the biosynthesis of essential mycobacterial cell wall components, such as the mycolyl-arabinogalactan-peptidoglycan complex and lipoarabinomannan; thus, its synthesis has attracted considerable interest as a potential therapeutic target. Rv1086 is a unique prenyl diphosphate synthase in that it adds only one isoprene unit to geranyl diphosphate, generating the 15-carbon product (E,Z-farnesyl diphosphate). Rv2361c then adds a further seven isoprene units to E,Z-farnesyl diphosphate in a processive manner to generate the 50-carbon prenyl diphosphate, which is then dephosphorylated to generate a carrier for activated sugars. The molecular basis for chain-length discrimination by Rv1086 during synthesis is unknown. We also report the structure of apo Rv1086 with citronellyl diphosphate bound and with the product mimic E,E-farnesyl diphosphate bound. We report the structures of Rv2361c in the apo form, with isopentenyl diphosphate bound and with a substrate analogue, citronellyl diphosphate. The structures confirm the enzymes are very closely related. Detailed comparison reveals structural differences that account for chain-length control in Rv1086. We have tested this hypothesis and have identified a double mutant of Rv1086 that makes a range of longer lipid chains.

Maize cDNAs expressed in endosperm encode functional farnesyl diphosphate synthase with geranylgeranyl diphosphate synthase activity

Isoprenoids are the most diverse and abundant group of natural products. In plants, farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP) are precursors to many isoprenoids having essential functions. Terpenoids and sterols are derived from FPP, whereas gibberellins, carotenoids, casbenes, taxenes, and others originate from GGPP. The corresponding synthases (FPP synthase [FPPS] and GGPP synthase [GGPPS]) catalyze, respectively, the addition of two and three isopentenyl diphosphate molecules to dimethylallyl diphosphate. Maize (Zea mays L. cv B73) endosperm cDNAs encoding isoprenoid synthases were isolated by functional complementation of Escherichia coli cells carrying a bacterial gene cluster encoding all pathway enzymes needed for carotenoid biosynthesis, except for GGPPS. This approach indicated that the maize gene products were functional GGPPS enzymes. Yet, the predicted enzyme sequences revealed FPPS motifs and homology with FPPS enzymes. In vitro assays demonstrated that indeed these maize enzymes produced both FPP and GGPP and that the N-terminal sequence affected the ratio of FPP to GGPP. Their functionality in E. coli demonstrated that these maize enzymes can be coupled with a metabolon to provide isoprenoid substrates for pathway use, and suggests that enzyme bifunctionality can be harnessed. The maize cDNAs are encoded by a small gene family whose transcripts are prevalent in endosperm beginning mid development. These maize cDNAs will be valuable tools for assessing the critical structural properties determining prenyl transferase specificity and in metabolic engineering of isoprenoid pathways, especially in cereal crops.

Mycobacterial lipid II is composed of a complex mixture of modified muramyl and peptide moieties linked to decaprenyl phosphate

Structural analysis of compounds identified as lipid I and II from Mycobacterium smegmatis demonstrated that the lipid moiety is decaprenyl phosphate; thus, M. smegmatis is the first bacterium reported to utilize a prenyl phosphate other than undecaprenyl phosphate as the lipid carrier involved in peptidoglycan synthesis. In addition, mass spectrometry showed that the muropeptides from lipid I are predominantly N-acetylmuramyl-L-alanine-D-glutamate-meso-diaminopimelic acid-D-alanyl-D-alanine, whereas those isolated from lipid II form an unexpectedly complex mixture in which the muramyl residue and the pentapeptide are modified singly and in combination. The muramyl residue is present as N-acetylmuramic acid, N-glycolylmuramic acid, and muramic acid. The carboxylic functions of the peptide side-chains of lipid II showed three types of modification, with the dominant one being amidation. The preferred site for amidation is the free carboxyl group of the meso-diaminopimelic acid residue. Diamidated species were also observed. The carboxylic function of the terminal D-alanine of some molecules is methylated, as are all three carboxylic acid functions of other molecules. This study represents the first structural analysis of mycobacterial lipid I and II and the first report of extensive modifications of these molecules. The observation that lipid I was unmodified strongly suggests that the lipid II intermediates of M. smegmatis are substrates for a variety of enzymes that introduce modifications to the sugar and amino acid residues prior to the synthesis of peptidoglycan.

Identification of a novel class of omega,E,E-farnesyl diphosphate synthase from Mycobacterium tuberculosis

We have identified an omega,E,E-farnesyl diphosphate (omega,E,E-FPP) synthase, encoded by the open reading frame Rv3398c, from Mycobacterium tuberculosis that is unique among reported FPP synthases in that it does not contain the type I (eukaryotic) or the type II (eubacterial) omega,E,E-FPP synthase signature motif. Instead, it has a structural motif similar to that of the type I geranylgeranyl diphosphate synthase found in Archaea. Thus, the enzyme represents a novel class of omega,E,E-FPP synthase. Rv3398c was cloned from the M. tuberculosis H37Rv genome and expressed in Mycobacterium smegmatis using a new mycobacterial expression vector (pVV2) that encodes an in-frame N-terminal affinity tag fusion with the protein of interest. The fusion protein was well expressed and could be purified to near homogeneity, allowing facile kinetic analysis of recombinant Rv3398c. Of the potential allylic substrates tested, including dimethylallyl diphosphate, only geranyl diphosphate served as an acceptor for isopentenyl diphosphate. The enzyme has an absolute requirement for divalent cation and has a K(m) of 43 microM for isopentenyl diphosphate and 9.8 microM for geranyl diphosphate and is reported to be essential for the viability of M. tuberculosis.

Identification and characterization of a cDNA encoding a long-chain cis-isoprenyltranferase involved in dolichyl monophosphate biosynthesis in the ER of brain cells

A long-chain cis-isoprenyltransferase (cis-IPTase) located in the endoplasmic reticulum (ER) catalyzes the chain elongation stage in the pathway for the de novo biosynthesis of dolichyl monophosphate (Dol-P) in eukaryotic cells. In Saccharomyces cerevisiae, the ER-associated cis-IPTase is encoded by the RER2 gene. Mutations in the RER2 gene result in defects in growth and protein N-glycosylation. In this study a cDNA isolated from human brain (Accession No. AK023164.1), which has substantial homology to cis-IPTases from bacteria, Arabidopsis, and S. cerevisiae, has been shown to: (1) complement the growth defect; (2) restore cis-IPTase activity; dolichol and Dol-P synthesis; and (3) restore normal N-glycosylation of carboxypeptidase Y (CPY) in the yeast rer2Delta mutant. Consistent with a role in Dol-P biosynthesis, overexpression of the human cis-isoprenyltransferase (hCIT) cDNA also suppresses the temperature-sensitive growth and CPY hypoglycosylation phenotypes in sec59-1 cells which are defective in Dol-P biosynthesis due to a temperature-sensitive mutation in dolichol kinase. Overexpression of hCIT in Chinese hamster ovary (CHO) cells results in a modest increase in cis-IPTase activity associated with microsomal fractions and the appearance of a new 38kDa polypeptide that co-localizes with calnexin in the ER, the site of Dol-P biosynthesis, even though no transmembrane domains are predicted by a hydropathy plot.

Unique mechanism of action of the thiourea drug isoxyl on Mycobacterium tuberculosis

The thiourea isoxyl (thiocarlide; 4,4'-diisoamyloxydiphenylthiourea) is known to be an effective anti-tuberculosis drug, active against a range of multidrug-resistant strains of Mycobacterium tuberculosis and has been used clinically. Little was known of its mode of action. We now demonstrate that isoxyl results in a dose-dependent decrease in the synthesis of oleic and, consequently, tuberculostearic acid in M. tuberculosis with complete inhibition at 3 microg/ml. Synthesis of mycolic acid was also affected. The anti-bacterial effect of isoxyl was partially reversed by supplementing growth medium with oleic acid. The specificity of this inhibition pointed to a Delta9-stearoyl desaturase as the drug target. Development of a cell-free assay for Delta9-desaturase activity allowed direct demonstration of the inhibition of oleic acid synthesis by isoxyl. Interestingly, sterculic acid, a known inhibitor of Delta9-desaturases, emulated the effect of isoxyl on oleic acid synthesis but did not affect mycolic acid synthesis, demonstrating the lack of a relationship between the two effects of the drug. The three putative fatty acid desaturases in the M. tuberculosis genome, desA1, desA2, and desA3, were cloned and expressed in Mycobacterium bovis BCG. Cell-free assays and whole cell labeling demonstrated increased Delta9-desaturase activity and oleic acid synthesis only in the desA3-overexpressing strain and an increase in the minimal inhibitory concentration for isoxyl, indicating that DesA3 is the target of the drug. These results validate membrane-bound Delta9-desaturase, DesA3, as a new therapeutic target, and the thioureas as anti-tuberculosis drugs worthy of further development.

Evidence that the wzxE gene of Escherichia coli K-12 encodes a protein involved in the transbilayer movement of a trisaccharide-lipid intermediate in the assembly of enterobacterial common antigen

The assembly of many bacterial cell surface polysaccharides requires the transbilayer movement of polyisoprenoid-linked saccharide intermediates across the cytoplasmic membrane. It is generally believed that transverse diffusion of glycolipid intermediates is mediated by integral membrane proteins called translocases or "flippases." The bacterial genes proposed to encode these translocases have been collectively designated wzx genes. The wzxE gene of Escherichia coli K-12 has been implicated in the transbilayer movement of Fuc4NAc-ManNAcA-GlcNAc-P-P-undecaprenol (lipid III), the donor of the trisaccharide repeat unit in the biosynthesis of enterobacterial common antigen (ECA). Previous studies (Feldman, M. F., Marolda, C. L., Monteiro, M. A., Perry, M. B., Parodi, A. J., and Valvano, M. (1999) J. Biol. Chem. 274, 35129-35138) provided indirect evidence that the wzx(016) gene product of E. coli K-12 encoded a translocase capable of mediating the transbilayer movement of N-acetylglucosaminylpyrophosphorylundecaprenol (GlcNAc-P-P-Und), an early intermediate in the synthesis of ECA and many lipopolysaccharide O antigens. Therefore, genetic and biochemical studies were conducted to determine if the putative Wzx(O16) translocase was capable of mediating the transport of N-acetylglucosaminylpyrophosphorylnerol (GlcNAc-P-P-Ner), a water-soluble analogue of GlcNAc-P-P-Und. [(3)H]GlcNAc-P-P-Ner was transported into sealed, everted cytoplasmic membrane vesicles of E. coli K-12 as well as a deletion mutant lacking both the wzx(016) and wzxC genes. In contrast, [(3)H]GlcNAc-P-P-Ner was not transported into membrane vesicles prepared from a wzxE-null mutant, and metabolic radiolabeling experiments revealed the accumulation of lipid III in this mutant. The WzxE transport system exhibited substrate specificity by recognizing both a pyrophosphoryl-linked saccharide and an unsaturated alpha-isoprene unit in the carrier lipid. These results support the conclusion that the wzxE gene encodes a membrane protein involved in the transbilayer movement of lipid III in E. coli.

Identification, cloning, purification, and enzymatic characterization of Mycobacterium tuberculosis 1-deoxy-D-xylulose 5-phosphate synthase

The enzyme encoded by Rv2682c in Mycobacterium tuberculosis is a functional 1-deoxy-D-xylulose 5-phosphate synthase (DXS), suggesting that the pathogen utilizes the mevalonate-independent pathway for isopentenyl diphosphate and subsequent polyprenyl phosphate synthesis. These key precursors are vital in the biosynthesis of many essential aspects of the mycobacterial cell wall. Rv2682c encodes the conserved DRAG sequence that has been proposed as a signature motif for DXSs and also all 13 conserved amino acid residues thought to be important to the function of transketolase enzymes. Recombinant Rv2682c is capable of utilizing glyceraldehyde 3-phosphate and erythrose 4-phosphate as well as D- and L-glyceraldehyde as aldose substrates. The enzyme has K(m) values of 40 microM, 6.1 microM, 5.6 mM, and 4.5 mM for pyruvate, D-glyceraldehyde 3-phosphate, D-glyceraldehyde, and L-glyceradehyde, respectively. Rv2682c has an absolute requirement for divalent cation and thiamin diphosphate as cofactors. The K(d) (thiamin diphosphate )for the native M. tuberculosis DXS activity partially purified from M. tuberculosis cytosol is 1 microM in the presence of Mg(2+).

Identification and characterization of a cDNA encoding a dolichyl pyrophosphate phosphatase located in the endoplasmic reticulum of mammalian cells

The CWH8 gene in Saccharomyces cerevisiae has been shown recently (Fernandez, F., Rush, J. S., Toke, D. A., Han, G., Quinn, J. E., Carman, G. M., Choi, J.-Y., Voelker, D. R., Aebi, M., and Waechter, C. J. (2001) J. Biol. Chem. 276, 41455-41464) to encode a dolichyl pyrophosphate (Dol-P-P) phosphatase associated with crude microsomal fractions. Mutations in CWH8 result in the accumulation of Dol-P-P, deficiency in lipid intermediate synthesis, defective protein N-glycosylation, and a reduced growth rate. A cDNA (DOLPP1, GenBank accession number AB030189) from mouse brain encoding a homologue of the yeast CWH8 gene is now shown to complement the defects in growth and protein N-glycosylation, and to correct the accumulation of Dol-P-P in the cwh8Delta yeast mutant. Northern blot analyses demonstrate a wide distribution of the DOLPP1 mRNA in mouse tissues. Overexpression of Dolpp1p in yeast, COS, and Sf9 cells produces substantial increases in Dol-P-P phosphatase activity but not in dolichyl monophosphate or phosphatidic acid phosphatase activities in microsomal fractions. Subcellular fractionation and immunofluorescence studies localize the enzyme encoded by DOLPP1 to the endoplasmic reticulum of COS cells. The results of protease sensitivity studies with microsomal vesicles from the lpp1Delta/dpp1Delta yeast mutant expressing DOLPP1 are consistent with Dolpp1p having a luminally oriented active site. The sequence of the DOLPP1 cDNA predicts a polypeptide with 238 amino acids, and a new polypeptide corresponding to 27 kDa is observed when DOLPP1 is expressed in yeast, COS, and Sf9 cells. This study is the first identification and characterization of a cDNA clone encoding an essential component of a mammalian lipid pyrophosphate phosphatase that is highly specific for Dol-P-P. The specificity, subcellular location, and topological orientation of the active site described in the current study strongly support a role for Dolpp1p in the recycling of Dol-P-P discharged during protein N-glycosylation reactions on the luminal leaflet of the endoplasmic reticulum in mammalian cells.

Chromatography of long chain alcohols (polyprenols) from animal and plant sources

This paper provides a comprehensive overview of existing chromatographic methods for the analysis of long chain alcohols (polyprenols) from animal and plant sources. After a brief introductory discussion on the biological aspects of the polyprenols, the review focuses on various techniques for the isolation, purification, chromatographic separation and detection of polyprenols.

Polyprenyl phosphate biosynthesis in Mycobacterium tuberculosis and Mycobacterium smegmatis

Mycobacterium smegmatis has been shown to contain two forms of polyprenyl phosphate (Pol-P), while Mycobacterium tuberculosis contains only one. Utilizing subcellular fractions from M. smegmatis and M. tuberculosis, we show that Pol-P synthesis is different in these species. The specific activities of the prenyl diphosphate synthases in M. tuberculosis are 10- to 100-fold lower than those in M. smegmatis. In M. smegmatis decaprenyl diphosphate and heptaprenyl diphosphate were the main products synthesized in vitro, whereas in M. tuberculosis only decaprenyl diphosphate was synthesized. The data from both organisms suggest that geranyl diphosphate is the allylic substrate for two distinct prenyl diphosphate synthases, one located in the cell membrane that synthesizes omega,E,Z-farnesyl diphosphate and the other present in the cytosol that synthesizes omega,E,E,E-geranylgeranyl diphosphate. In M. smegmatis, the omega,E, Z-farnesyl diphosphate is utilized by a membrane-associated prenyl diphosphate synthase activity to generate decaprenyl diphosphate, and the omega,E,E,E-geranylgeranyl diphosphate is utilized by a membrane-associated activity for the synthesis of the heptaprenyl diphosphate. In M. tuberculosis, however, omega,E,E,E-geranylgeranyl diphosphate is not utilized for the synthesis of heptaprenyl diphosphate. Thus, the difference in the compositions of the Pol-P of M. smegmatis and M. tuberculosis can be attributed to distinct enzymatic differences between these two organisms.

Identification of a short (C15) chain Z-isoprenyl diphosphate synthase and a homologous long (C50) chain isoprenyl diphosphate synthase in Mycobacterium tuberculosis

We report the cloning, overexpression, and partial characterization of two unique Z-isoprenyl diphosphate synthase homologs from Mycobacterium tuberculosis. The first enzyme, Rv1086, adds one isoprene unit to omega,E-geranyl diphosphate. The product, omega,E, Z-farnesyl diphosphate, is the putative substrate of the second enzyme, Rv2361c. This enzyme adds seven more isoprene units to omega, E,Z-farnesyl diphosphate and releases decaprenyl diphosphate. Both open reading frames were cloned from the M. tuberculosis H37Rv genome and overexpressed in M. smegmatis. Membrane and cytosol fractions from wild type and the two recombinant strains were assayed for [(14)C]isopentenyl diphosphate incorporation into isoprenyl diphosphates in the presence of various allylic isoprenyl diphosphate acceptors. Membrane fractions of recombinant cells overexpressing Rv2361c incubated with farnesyl diphosphate showed a 10-fold increase of [(14)C]isopentenyl diphosphate incorporation into decaprenyl diphosphate. Membrane fractions of recombinant cells overexpressing Rv1086 incubated with geranyl diphosphate showed a 5-fold increase of [(14)C]isopentenyl diphosphate incorporation into farnesyl diphosphate. Analysis of the stereochemistry revealed that all of the overexpressed farnesyl diphosphate was in the omega,E, Z-configuration. This is the first description of a short chain isoprenyl diphosphate synthase that generates products with Z-stereochemistry. Previously, all known short chain isoprenyl diphosphate synthases catalyze the synthesis of products with E-stereochemistry.

Design and synthesis of a transferable farnesyl pyrophosphate analogue to Ras by protein farnesyltransferase

The posttranslational addition of a farnesyl moiety to the Ras oncoprotein is essential for its membrane localization and is required for both its biological activity and ability to induce malignant transformation. We describe the design and synthesis of a farnesyl pyrophosphate (FPP) analogue, 8-anilinogeranyl pyrophosphate 3 (AGPP), in which the omega-terminal isoprene unit of the farnesyl group has been replaced with an aniline functionality. The key steps in the synthesis are the reductive amination of the alpha,beta-unsaturated aldehyde 5 to form the lipid analogue 6, and the subsequent conversion of the allylic alcohol 7 to the chloride 8 via Ph(3)PCl(2) followed by displacement with [(n-Bu)(4)N](3)HP(2)O(7) to give AGPP (3). AGPP is a substrate for protein farnesyltransferase (FTase) and is transferred to Ras by FTase with the same kinetics as the natural substrate, FPP. AGPP is highly selective, showing little inhibitory activity against either geranylgeranyl-protein transferase type I (GGTase I) (K(i) = 0.06 microM, IC(50) = 20 microM) or squalene synthase (IC(50) = 1000 microM). AGPP is the first efficiently transferable analogue of FPP to be modified at the omega-terminus that provides a platform from which additional analogues can be made to probe the biological function of protein farnesylation. AGPP is the first example of a class of compounds that are alternate substrates for protein isoprenylation that are not inhibitors of squalene synthase.

Farnesol is utilized for isoprenoid biosynthesis in plant cells via farnesyl pyrophosphate formed by successive monophosphorylation reactions

The ability of Nicotiana tabacum cell cultures to utilize farnesol (F-OH) for sterol and sesquiterpene biosynthesis was investigated. [(3)H]F-OH was readily incorporated into sterols by rapidly growing cell cultures. However, the incorporation rate into sterols was reduced by greater than 70% in elicitor-treated cell cultures whereas a substantial proportion of the radioactivity was redirected into capsidiol, an extracellular sesquiterpene phytoalexin. The incorporation of [(3)H]F-OH into sterols was inhibited by squalestatin 1, suggesting that [(3)H]F-OH was incorporated via farnesyl pyrophosphate (F-P-P). Consistent with this possibility, N. tabacum proteins were metabolically labeled with [(3)H]F-OH or [(3)H]geranylgeraniol ([(3)H]GG-OH). Kinase activities converting F-OH to farnesyl monophosphate (F-P) and, subsequently, F-P-P were demonstrated directly by in vitro enzymatic studies. [(3)H]F-P and [(3)H]F-P-P were synthesized when exogenous [(3)H]F-OH was incubated with microsomal fractions and CTP. The kinetics of formation suggested a precursor-product relationship between [(3)H]F-P and [(3)H]F-P-P. In agreement with this kinetic pattern of labeling, [(32)P]F-P and [(32)P]F-P-P were synthesized when microsomal fractions were incubated with F-OH and F-P, respectively, with [gamma-(32)P]CTP serving as the phosphoryl donor. Under similar conditions, the microsomal fractions catalyzed the enzymatic conversion of [(3)H]GG-OH to [(3)H]geranylgeranyl monophosphate and [(3)H]geranylgeranyl pyrophosphate ([(3)H]GG-P-P) in CTP-dependent reactions. A novel biosynthetic mechanism involving two successive monophosphorylation reactions was supported by the observation that [(3)H]CTP was formed when microsomes were incubated with [(3)H]CDP and either F-P-P or GG-P-P, but not F-P. These results document the presence of at least two CTP-mediated kinases that provide a mechanism for the utilization of F-OH and GG-OH for the biosynthesis of isoprenoid lipids and protein isoprenylation.

Transbilayer movement of Glc-P-dolichol and its function as a glucosyl donor: protein-mediated transport of a water-soluble analog into sealed ER vesicles from pig brain

The results described in the accompanying article support the model in which glucosylphosphoryldolichol (Glc-P-Dol) is synthesized on the cytoplasmic face of the ER, and functions as a glucosyl donor for three Glc-P-Dol:Glc0-2Man9-GlcNAc2-P-P-Dol glucosyltransferases (GlcTases) in the lumenal compartment. In this study, the enzymatic synthesis and structural characterization by NMR and electrospray-ionization tandem mass spectrometry of a series of water-soluble beta-Glc-P-Dol analogs containing 2-4 isoprene units with either the cis - or trans -stereoconfiguration in the beta-position are described. The water-soluble analogs were (1) used to examine the stereospecificity of the Glc-P-Dol:Glc0-2Man9GlcNAc2-P-P-Dol glucosyltransferases (GlcTases) and (2) tested as potential substrates for a membrane protein(s) mediating the transbilayer movement of Glc-P-Dol in sealed ER vesicles from rat liver and pig brain. The Glc-P-Dol-mediated GlcTases in pig brain microsomes utilized [3H]Glc-labeled Glc-P-Dol10, Glc-P-(omega, c )Dol15, Glc-P(omega, t,t )Dol20, and Glc-P-(omega, t,c )Dol20as glucosyl donors with [3H]Glc3Man9GlcNAc2-P-P-Dol the major product labeled in vitro. A preference was exhibited for C15-20 substrates containing an internal cis -isoprene unit in the beta-position. In addition, the water-soluble analog, Glc-P-Dol10, was shown to enter the lumenal compartment of sealed microsomal vesicles from rat liver and pig brain via a protein-mediated transport system enriched in the ER. The properties of the ER transport system have been characterized. Glc-P-Dol10was not transported into or adsorbed by synthetic PC-liposomes or bovine erythrocytes. The results of these studies indicate that (1) the internal cis -isoprene units are important for the utilization of Glc-P-Dol as a glucosyl donor and (2) the transport of the water-soluble analog may provide an experimental approach to assay the hypothetical "flippase" proposed to mediate the transbilayer movement of Glc-P-Dol from the cytoplasmic face of the ER to the lumenal monolayer.

Expression cloning of a novel farnesylated protein, RDJ2, encoding a DnaJ protein homologue

The CAAX farnesyltransferase is a heterodimeric enzyme that attaches a farnesyl group to a single cysteine in cellular proteins which terminate in the sequence CAAX, where C is cysteine, A is an aliphatic amino acid, and X is most often methionine or serine. Substrates include the p21ras proteins, nuclear lamins, and a series of retinal proteins. To date, a limited number of substrates for the farnesyltransferase have been identified, predominantly by demonstration of the attachment of a farnesyl group to previously identified cDNA clones which encode proteins containing an appropriate carboxyl-terminal tetrapeptide. We describe here the use of a cDNA fusion protein expression library, together with enzymatic in vitro [3H]farnesyl radiolabeling, as a means of identifying novel farnesylated proteins. One candidate cDNA was fully cloned and found to be a homologue of the Escherichia coli heat shock gene dnaJ. The predicted amino acid sequence of this protein was found to terminate with the tetrapeptide Cys-Ala-His-Gln, which conforms to the consensus sequence for recognition by farnesyltransferase, and was shown to undergo in vivo farnesylation. This farnesylated protein, designated RDJ2 (rat DnaJ homologue 2), is a novel and ubiquitously expressed DnaJ homologue and is the newest member of the subfamily of DnaJ-related proteins which are posttranslationally modified by protein farnesylation.

Progesterone stimulation of HMG-CoA reductase activity in cultured cells

In a previous study we showed that progesterone (PG) stimulated HMG-CoA reductase (HMGR) activity in rat intestinal epithelial cells (IEC-6) incubated in the presence or absence of low-density lipoprotein (LDL) [1,2]. In the present study we examined further the mechanism of this stimulation. We observed that the stimulation of HMGR activity by PG was completely prevented by cycloheximide. Turnover studies utilizing immunoprecipitation of HMGR-labeled with [35S]methionine revealed that PG increased reductase activity by inhibiting HMGR degradation without affecting the synthesis of HMGR. The stimulation of HMGR activity by progesterone could be accounted for by a continuous synthesis of HMGR while its degradation was retarded. In the presence of LDL, the activity of HMGR in IEC-6 cells was effectively inhibited, however PG was able to stimulate HMGR in the presence of LDL. This effect was not due to an interference of normal cellular metabolism of LDL, since PG had no effect on the cellular uptake and lysosomal degradation of 125I-LDL. PG did not affect of the rate of lysosomal hydrolysis of [3H]cholesteryl linoleate-LDL. The free [3H]cholesterol derived from [3H]cholesteryl linoleate-LDL moved to the cell membrane and effluxed to HDL3 in the medium at the same rate in the presence or absence of PG. Although PG did not affect LDL metabolism, pre-treatment of cells with LDL delayed the onset of HMGR stimulation by PG. In IEC-6 cells deprived of LDL for 24 h, the HMGR activity was stimulated immediately following PG addition. In cells pre-treated with LDL for 24 h, the stimulation was delayed by 4 h. Treatment of cells with 25-hydroxycholesterol completely prevented PG stimulation of HMGR activity. We propose that the stimulation of HMGR activity in the presence or absence of LDL is related to the ability of PG to attenuate the formation and/or action of intracellular HMGR repressor molecules which accelerate the degradation of HMGR.

Long-chain cis-isoprenyltransferase activity is induced early in the developmental program for protein N-glycosylation in embryonic rat brain cells

A large developmental increase in Glc3Man9-GlcNAc2-P-P-dolichol (Oligo-P-P-Dol) synthesis and protein N-glycosylation in primary cultures of embryonic rat brain cells has been reported previously. In vitro enzyme studies and metabolic labeling experiments now show that there is a coordinate induction of long-chain cis-isoprenyltransferase (IPTase) activity, an activity required for the chain-elongation stage of dolichyl monophosphate (Dol-P) biosynthesis de novo, and Oligo-P-P-Dol biosynthesis in embryonic rat brain. Different developmental patterns were observed for IPTase and beta-hydroxy-beta-methyl-glutaryl-CoA (HMG-CoA) reductase activity as well as Dol-P and cholesterol biosynthesis, indicating that these pathways are regulated independently in rat brain. Three separate experimental approaches provide evidence that the amount of Dol-P available in the rough endoplasmic reticulum (RER) is a rate-limiting factor in the expression of the lipid intermediate pathway. First, metabolic labeling experiments show that the biosynthesis of Dol-P is induced at the same time or just prior to the induction of Oligo-P-P-Dol biosynthesis. Second, the time of induction and rate of Oligo-P-P-Dol synthesis are accelerated when Dol-P is supplemented in the culture medium. Third, in vitro assays of mannosylphosphoryldolichol synthase and N-acetylglucosaminylpyrophosphoryldolichol synthase indicate that there are only minor increases in the levels of these enzymes during development, but the amount of endogenous Dol-P in the RER that is accessible to the glycosyltransferases increases when IPTase activity is induced. In summary, the current studies with embryonic rat brain cells document the coordinate induction of IPTase activity and Oligo-P-P-Dol synthesis, support the hypothesis that the availability of Dol-P in the RER is one rate-limiting factor in Oligo-P-P-Dol synthesis, and strongly suggest that increases in IPTase activity and the rate of de novo Dol-P biosynthesis enhance the capacity of embryonic rat brain cells for lipid intermediate synthesis early in the developmental program for N-linked glycoprotein biosynthesis.

Short-chain dolichols of defined chain length as cofactors in reactions of the microsomal dolichyl-phosphate cycle and transglycosylations

1) The biological cofactor and carrier activities of dolichyl phosphates of low isoprene multiplicity (n) and defined geometry, (synthesized according to L. Jaenicke and H.-U. Siegmund, Chem. Phys. Lipids 51 (1989) 159-170), were assayed in different transfer reactions of the microsomal dolichyl-phosphate cycle against natural pig liver dolichyl phosphate (n = 18 to 20). 2) The apparent Michaelis constants and maximal velocities were determined from initial reaction rates for the transfer from GDP-mannose, UDP-N-acetylglucosamine, and UDP-glucose to the synthetic truncated dolichyl phosphates. They afford quantitative comparison and show increasing biological activities from dolichyl-6 phosphate to dolichyl-11 phosphate, which is about as active as the natural mixture. This is in accord with previous findings on the starting reactions of the cycle. 3) Truncated dolichyl diphosphochitobioses, biosynthesized in vitro from synthetic dolichyl phosphates, were used as acceptors for nucleoside diphosphohexoses in solubilized membranes. All of them show about the same activity. The kinetics and yield were determined for each of the transfers. Activity is increased by adding UDP-glucose. The inactive very short-chain dolichol compounds do not interfere with the transfer to active longer chain dolichols. 4) The oligosaccharides produced by transfer of mannose and glucose to truncated dolichyl diphosphate-bound chitobiose were isolated and analysed for sugar multiplicity. The heptasaccharide and the un-decasaccharide are accumulated most, pointing to the transport across the endoplasmic membranes (ER) as the rate limiting reaction. 5) The truncated dolichyl-diphosphate-bound oligosaccharides are transferred to protein(s) by the crude, solubilized microsomal preparation independent of chain length of the cofactor/carrier, yet with increasing yield as shown by enzyme immunoblot analysis.

Nucleotide-activated oligosaccharides are intermediates of the cell wall polysaccharide of Methanosarcina barkeri

The cell wall of Methanosarcina barkeri consists of a heteropolysaccharide (methanochondroitin), which resembles the eukaryotic chondroitin. From cell extracts of Methanosarcina barkeri four uridine diphosphate and one undecaprenyl pyrophosphate-activated intermediate(s) of the methanochondroitin were isolated. In contrast to the known biosynthetic pathways of polysaccharides from other prokaryotes and eukaryotes, nucleotide activated oligosaccharide precursors are involved in the case of the methanochondroitin. Usually, oligosaccharides are synthesized at the lipid stage.

Characterization and localization of a long-chain isoprenyltransferase activity in porcine brain: proposed role in the biosynthesis of dolichyl phosphate

Pig brain microsomes catalyzed the enzymatic transfer of radiolabeled isoprenyl groups from [1-14C]isopentenyl pyrophosphate [( 1-14C]I-P-P) into long-chain polyisoprenyl pyrophosphates (Poly-P-P) and unidentified neutral lipids. The brain isoprenyltransferase activity synthesizing the Poly-P-P (1) required 5 mM Mg2+ and 10 mM vanadate ions for maximal activity; (2) exhibited an apparent Km of 8 microM for I-P-P; (3) utilized exogenous farnesyl pyrophosphate and two stereoisomers of geranylgeranyl pyrophosphate as substrates; (4) was optimal at pH 8.5; and (5) was stimulated by dithiothreitol. The major products were identified as C90 and C95 allylic Poly-P-P on the basis of the following chemical and chromatographic properties: (1) the intact product co-chromatographed with authentic Poly-P-P on silica-gel-impregnated paper; (2) the major product was converted to a compound chromatographically identical to polyisoprenyl monophosphate (Poly-P) by alkaline hydrolysis; (3) treatment of the labeled Poly-P with wheat germ acid phosphatase or mild acid yielded neutral labeled products; (4) the KOH hydrolyzed product coeluted with authentic Poly-P from lipophilic Sephadex LH-20; and (5) the labeled lipids produced by enzymatic dephosphorylation had mobilities identical to fully unsaturated polyisoprenols containing 18 (C90) and 19 (C95) isoprene units when analyzed by reverse-phase chromatography. When subcellular fractions from rat brain gray matter were compared, the highest specific activity was found in the heavy microsomes. These results demonstrate that brain contains an isoprenyltransferase activity, associated with the rough endoplasmic reticulum, capable of synthesizing long-chain Poly-P-P. The enzymatic reactions by which the Poly-P-P intermediate is converted to dolichyl phosphate remain to be elucidated.

Isolation of lipid activated pseudomurein precursors from Methanobacterium thermoautotrophicum

From cell extracts of the pseudomurein possessing methanogen Methanobacterium thermoautotrophicum two putative pseudomurein precursors were isolated and characterized: (1) an undecaprenyl pyrophosphate activated disaccharide pentapeptide composed of N-acetylglucosamine, N-acetyltalosaminuronic acid, alanine, glutamic acid and lysine in a molar ratio of 1:1:2:2:1 and (2) the corresponding undecaprenyl pyrophosphate activated tetrapeptide lacking one alanine residue. The isolation of these precursors show that the biosynthesis of the eubacterial murein and the methanobacterial pseudomurein differs not only in the cytoplasmic step, as recently described, but also in the lipid stage.

Lipid abnormalities in the brain in adult Down's syndrome and Alzheimer's disease

Quantitative analysis by HPTLC of the major lipid classes and dolichol, and of fatty acyl groups of separated phosphoglycerides by capillary GLC, has been carried out on the gray matter of frontal cerebral cortex of brains from six Down's syndrome (DS) and six Alzheimer's disease (AD) adults, and six each of two corresponding sets of age-matched controls; specimens of DS and control cerebellum and corpus callosum were also analyzed. In DS frontal cortex, but not in AD frontal cortex, compared to their respective controls there was a decrease in the fraction of phosphatidylethanolamine (PE) and an increase in the fractions of sphingomyelin (SPM) and phosphatidylserine (PS). Abnormalities were not found in the proportions of major lipid classes in DS cerebellum or corpus callosum. The concentration of dolichol was elevated for age in the frontal cortex of DS and of AD. In the phosphoglycerides of DS frontal cortex, the fatty acyl composition showed small, but statistically significant, differences from those of age-matched controls, and some slight abnormalities were also detected in DS corpus callosum. The alterations in DS frontal cortex included decreases in (n-6) and increases in (n-3) groups in choline and ethanolamine phosphoglycerides (CPG and EPG), as had previously been found in EPG and serine phosphoglyceride (SPG) of the DS fetal brain. In DS frontal cortex, the proportion of 22:4(n-6) groups was decreased in SPG, and in inositol phosphoglyceride (IPG) 18:1(n-9) was increased. There were also small but significant alterations in DS frontal cortex in the fractions of shorter chain groups in CPG. In marked contrast, most of the fatty acyl abnormalities seen in DS were absent in the AD frontal cortex. It is therefore suggested that some abnormalities in the composition of cerebral membranes present prenatally in DS may persist into adulthood, and are not directly related to AD-type pathology.

CTP-dependent lipid kinases of yeast

Membrane fractions from yeast Saccharomyces cerevisiae catalyzed a transfer of gamma-phosphate from [gamma-32P]CTP into membranous lipids. Phosphorylated compounds were identified as phosphatidic acid and dolichyl phosphate (DolP). The membrane fraction also catalyzed phosphorylation of the exogenous dolichol. The activity of the phosphorylating enzymes could be modified by the yeast growing conditions; i.e., the enzyme from yeast grown aerobically favored the synthesis of phosphatidate over dolichyl phosphate in the ratio of 3:1, whereas the membrane fraction from anaerobically grown yeast synthesized PA and DolP in the ratio of 0.5:1. The activity of the phosphorylating enzymes could also be modified by divalent cations and the concentration of detergents. Phosphorylation of lipids does not occur in the presence of [gamma-32P]ATP and is not influenced by the presence of UTP or GTP. This result points to the specific role of CTP as a gamma-phosphate donor for the synthesis of phosphatidate and dolichyl phosphates in the yeast system.

Incorporation of mevalonate into dolichol and other isoprenoids during estrogen-induced chick oviduct differentiation

Incorporation of [14C]mevalonate into dolichol and other isoprenoid compounds by chick oviduct explants has been studied. A reliable assay of dolichol biosynthesis employing several chromatographic procedures, including two-dimentional TLC, was developed. Incorporation of [14C]mevalonate into dolichol by oviduct explants was linear for at least 6 h. The effect of estrogen-induced differentiation was studied by incubation of explants obtained from chicks treated for various periods of time with diethylstilbestrol. Mevalonate incorporation into dolichol, when expressed as cpm per g of tissue, was not affected by estrogen treatment, but since the oviduct increased about 100-fold in mass during differentiation, each oviduct synthesizes about 100-fold more dolichol. In most tissues, the major product of mevalonate incorporation is cholesterol. However, although approx. 90% of the non-saponifiable 14C-labeled compounds were in the so-called 'cholesterol fraction', oviduct explants from estrogenized chicks synthesized little, if any, cholesterol. A number of cholesterol biosynthetic intermediates were observed, with compounds comigrating with squalene and lanosterol accounting for about 50% of the total. Since the estrogenized chick has serum cholesterol levels in the range of 800-900 mg/dl, these results suggest that oviduct has secondary control points which allow it to inhibit cholesterol synthesis when mevalonate is used as the precursor. In support of this hypothesis is the observation that explants from untreated chicks can incorporate mevalonate into cholesterol.

Biosynthesis, in calf pancreas microsomes, of three lipid-linked oligosaccharide diphosphates from a synthetic dolichyl diphosphate tetrasaccharide

Incubation of calf pancreas microsomes with synthetic alpha-D-Manp-(1----6)-beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1 ----4)-alpha-D- GlcpNAc-PP-Dol and GDP-D-[14C]-mannose gave three major lipid-linked oligosaccharide diphosphates. After release of the phospholipid residue by mild acid hydrolysis, the corresponding [14C]oligosaccharides were analyzed by gel-filtration, liquid chromatography, degradation by endo-N-acetyl-beta-D-glucosaminidases D and H, by jack bean alpha-D-mannosidase and Aspergillus oryzae (1----2)-alpha-D-mannosidase, acetolysis, and binding to concanavalin A-Sepharose. From the results it could be inferred that the following reaction took place in calf pancreas microsomes: alpha-D-Manp-(1----6)-beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1 ----4)-alpha-D- GlcpNAc-PP-Dol + GDP-D-Man gave GDP + alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)- beta-D-GlcpNAc-(1----4)-alpha-D-GlcpNAc-PP-Dol. The next products to be formed were alpha-D-Manp-(1----2)-alpha-D-Manp-(1----3)-[alpha-D-Manp -(1----6)]-beta-D- Manp-(1----4)-beta-D-GlcpNAc-(1----4)-alpha-D-GlcpNAc-PP-Dol, followed by alpha-D-Manp-(1----2)-alpha-D-Manp-(1----2)-alpha-D-Manp+ ++-(1----3)- [alpha-D-Manp-(1----6)]-beta-D-Manp-(1----4)-beta-D-GlcpNAc- (1----4)-alpha- D-GlcpNAc-PP-Dol. The mannose incorporation was enhanced by Triton X-100 and inhibited by Mn2+, and it occurred in the presence of either Mg2+ or EDTA. It is likely that the mannose donor was GDP-mannose since, under the conditions used, the formation of dolichyl mannosyl phosphate was negligible and the dolichyl heptasaccharide diphosphate accumulated.

The preparation of a partially protected heptasaccharide-asparagine intermediate for glycopeptide synthesis

The heptasaccharide O-alpha-D-mannopyranosyl-(1----6)-O-[alpha-D-mannopyranosyl-(1----3)]-O- alpha-D-mannopyranosyl-(1----6)-O-[alpha-D-mannopyranosyl-(1----3)]-O-be ta- D-mannopyranosyl-(1----4)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)- (1----4)-2-acetamido-2-deoxy-D-glucopyranose, isolated from the urine of swainsonine-intoxicated sheep, was peracetylated and was converted into the glycosyl azide by three alternative procedures, the most successful of which was formation of peracetyl oxazoline by treatment with trimethylsilyl trifluoromethanesulfonate, followed by treatment with trimethylsilyl azide. Reduction of the glycosyl azide in the presence of Lindlar catalyst gave the glycosylamine derivative, which was coupled with 1-benzyl N-fluoren-9-ylmethoxycarbonyl-L-aspartate to yield a protected glycosylasparagine. The benzyl ester group was easily removed by hydrogenolysis to form an intermediate suitable for glycopeptide synthesis.

Total synthesis of chain-length-uniform dolichyl phosphates and their fitness to accept hexoses in the enzymatic formation of lipoglycans

Dolichols of defined uniform chain length (C35, C45, and C55) and geometry were prepared by total synthesis according to the following principle: (E,E)-Farnesol, activated as its 4-tolyl sulfone, is condensed with 8-chloroneryl benzyl ether, the sulfonyl group removed and the ether linkage cleaved by lithium/triethylamine. The resulting elongated prenol is converted again to its corresponding 4-toly/sulfone; at this stage isomers are removed by chromatography. After several cycles of this C10-elongation sequence the synthesis is completed in the same way but using 8-chlorocitronellyl benzyl ether as building block to introduce the saturated alpha-isoprene unit. The dolichols obtained were chemically phosphorylated (POCl3/Et3N). Both, the alcohols and their phosphate esters, are characterized spectroscopically. 1H- and 13C-NMR data are recorded for qualitative and stereochemical comparison with natural dolichols. The authentic dolichyl phosphates (Dol-7-P, Dol-9-P, and Dol-11-P) were assayed relative to the natural dolichyl phosphate mixture from pig liver as acceptors for transglycosylation from nucleoside diphosphate sugars (glucose, mannose) by standardized membrane vesicle preparations from plants (Volvox) and animals (liver). Even the shortest chain dolichyl 7-phosphate has full activity in this lipoglycan-forming reaction.

Hydrolysis of dolichyl esters by oviduct membranes and characterization of endogenous dolichyl esters

The chick oviduct system has been employed to study whether dolichol esters might serve as a storage form of dolichol to be converted to dolichyl phosphate (Dol-P) during periods when Dol-P levels increase. Chicken oviduct membranes catalyze the hydrolysis of dolichyl-[14C]oleate; the reaction is dependent on detergent (0.04% NP-40 is optimal), is unaffected by divalent cations and EDTA, and exhibits a pH optimum of 6.0. Oviduct membranes also hydrolyze cholesteryl-[14C]oleate, which exhibits similar properties except the pH optimum is 5.0-5.5. Neither Dol-[14C]palmitate nor Chol-[14C]palmitate is hydrolyzed by membranes. Chol-ester hydrolysis is more sensitive to heat-denaturation than is Dol-ester hydrolysis. Esterase activity was assayed in membranes prepared from immature chicks, chicks treated with diethylstilbestrol, chicks withdrawn from diethylstilbestrol, and mature hens. The highest esterase specific activity was observed in membranes obtained from chicks withdrawn from hormone. In order to characterize the fatty acid composition of Dol-esters they were purified from mature hen oviducts by chromatography on DEAE-cellulose and Fractogel ORPVA-6000, reverse-phase HPLC, and TLC. About 15-25% of oviduct dolichol is in the esterified form. Fatty acid analysis revealed that approximately 85% of the dolichol was esterified to oleic acid. The fact that the highest esterase activity is found in membranes from chicks withdrawn from hormone and that only 20% of the dolichol is esterified argues against a role for Dol-esters as a reservoir of dolichol for conversion to Dol-P.

Properties of brain dolichol kinase activity solubilized with a zwitterionic detergent

Dolichol kinase activity is effectively solubilized by extracting calf brain microsomes with 2% 3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS), a zwitterionic detergent. The solubilized kinase catalyzes the enzymatic phosphorylation of dolichols with either CTP or dCTP serving as phosphoryl donor in the presence of Ca2+. Similar Km values were calculated for CTP (7.7 microM) and dCTP (9.1 microM). Dolichol phosphorylation was inhibited by CDP and dCDP, but not CMP, ADP, GDP, or UDP. A kinetic analysis of the inhibitory effect of CDP revealed a pattern characteristic of competitive inhibition. Dolichol kinase activity was markedly stimulated by the addition of R-dolichol (C95) or S-dolichol(C95). The apparent Km value for R-dolichol(C95) and S-dolichol(C95) was 9 microM, but the Vmax for the phosphorylation reaction was 40% higher with S-dolichol(C95). Incubation of the CHAPS extract with [gamma-32P]CTP and exogenous undecaprenol(C55) resulted in the enzymatic synthesis of a radiolabeled product that was mild acid-labile and chromatographically identical to undecaprenyl monophosphate. An enzymatic comparison with a variety of polyprenol substrates indicates that the solubilized kinase prefers long-chain (C90-95) polyprenols with saturated alpha-isoprene units. The effect of exogenous phosphoglycerides on the kinase activity in the dialyzed CHAPS extracts has also been evaluated. These studies describe the properties and polyprenol specificity of stable, solubilized preparations of dolichol kinase that should be useful for further purification of the enzyme.

Preparation of a glycosyl donor suitable for synthesis of glycoprotein "core" oligosaccharides

2-O-Acetyl-3-O-allyl-4-O-benzyl-6-O-tert-butyldiphenylsilyl-D-gluc opyranosyl chloride (14), a glycosyl donor suitable for synthesis of oligosaccharides corresponding to the N-glycoprotein saccharide "core", was synthesized by an efficient, six-stage route from 3,4,6-tri-O-acetyl-1,2-O-[1-(exo-ethoxy)ethylidene)-alpha-D-glucopyranos e. Silver triflate-promoted coupling of 14 with benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-alpha-D-glucopyranoside gave a protected beta-D-(1----4)-linked disaccharide in 38% yield, but a major side-reaction also occurred. When the tert-butyldiphenylsilyl group was quantitatively removed from 14 prior to the coupling reaction, and replaced afterwards, the yield in the glycosidation was increased to 55%, and major side-products were avoided.

Distribution, metabolism and function of dolichol and polyprenols

Polyisoprenoid alcohols consisting of 9 or more isoprene units are present in all living cells. They can be fully unsaturated (polyprenols) or alpha-saturated (dolichol). Dolichol forms may have additional saturation at or near the omega-end. Some species contain ony dolichol or only polyprenols while others have nearly equal amounts of both types. Some polyisoprenoid alcohols consist entirely of trans isoprene units but most, including dolichol, contain both trans and cis units. Considerable advances in lipid methodology have occurred since the first review of polyisoprenoid alcohols by Hemming in 1974. For example, direct analysis of both dolichol and Dol-P by HPLC has replaced earlier methods which were often both insensitive and inaccurate. The availability of radiolabeled dolichol and polyprenols has facilitated studies concerning the metabolism and distribution of these compounds. Those studies suggest that only a small portion of the dolichol present in cells is likely to be involved in glycosylation. Polyisoprenoid alcohols are usually present at a family of homologues where each differs in size by one isoprene unit. Little or no size related specificity has been observed for any reaction involving dolichol or polyisoprenol intermediates. The overall length of polyisoprenoid alcohols may, however, affect the manner in which these compounds influence the physical and biochemical properties of membranes. Studies on the biosynthetic pathway leading from cis, trans Pol-PP by phosphatase action. The formation of the dolichol backbone from a polyprenol requires the action of an additional enzyme, an alpha-saturase. This enzyme does not always act at the level of a single common substrate, since Pol-PP, Pol-P, and polyprenol all appear to be utilized as substrates. The major product of the de novo pathway differs among different species. Dol-P would appear to be the most energy efficient end-product since it can participate directly in glycoprotein formation. Most often, however, Dol-P is not the major product of metabolic labeling experiments. In some cases, dolichol is formed so that rephosphorylation is required to provide Dol-P for participation in glycoprotein formation. The kinase responsible for this phosphorylation appears to bypass the considerable stores of dolichol present in tissues (i.e. sea urchin eggs) in favor of dolichol derived directly from de novo synthesis. Although HMGR is a major regulatory component of the pathway leading to polyisoprenoid alcohols and cholesterol, control is most often not co-ordinated.(ABSTRACT TRUNCATED AT 400 WORDS)

Biosynthesis of polyisoprenoid lipids in the rat tapeworm Hymenolepis diminuta

The possible occurrence of isoprenoid lipids in the tapeworm, Hymenolepis diminuta, was investigated by analytic and biosynthetic methods. Two-dimensional thin layer chromatography (TLC) resolved the worm's non-saponifiable lipids into cholesterol, farnesol, and several unknown compounds, two of which migrated with dolichol standards on TLC and reacted with phthalic anhydride, a probe for alcohols; the major compound also exhibited a mass spectrum very similar to that of a dolichol standard. A third unknown compound separable by TLC, apparently a quinone, was intrinsically red, was decolorized by treatment with sodium dithionite and migrated on TLC in a more polar position than either ubiquinone-50 or vitamin K1. All three compounds, as well as farnesol, were labelled when worms were incubated with [14C]-mevalonolactone, suggesting that they are endogenous isoprenoids.