Sugar availability modulates polyisoprenoid and phytosterol profiles in Arabidopsis thaliana hairy root culture

Sugars are recognized as signaling molecules regulating the biosynthesis of secondary metabolites in plants. Here, a modulatory effect of sugars on dolichol and phytosterol profiles was noted in the hairy roots of Arabidopsis thaliana. Arabidopsis roots contain a complex dolichol mixture comprising three groups (‘families’) of dolichols differing in the chain-length. These dolichols, especially the longest ones are accompanied by considerable amounts of polyprenols of the same length. The spectrum of polyisoprenoid alcohols, i.e. dolichols and polyprenols, was dependent on sugar type (glucose or sucrose) and its concentration in the medium. Among the long-chain dolichols Dol/Pren-20 (dolichol or prenol molecule composed of 20 isoprene residues) and Dol/Pren-23 were the main components at 0.5% and 2% glucose, respectively. Moreover, the ratio of polyprenols versus respective dolichols was also modulated by sugar in this group of polyisoprenoids, with polyprenols dominating at 3% sucrose and dolichols at 2% glucose. Glucose concentration affected the expression level of genes encoding cis-prenyltransferases, enzymes responsible for elongation of the polyisoprenoid chain. The most abundant phytosterols of the A. thaliana roots, β-sitosterol, stigmasterol and campesterol, were accompanied by corresponding stanols and traces of brassicasterol, stigmast-4,22-dien-3-one and stigmast-4-en-3-one. Similar to the polyisoprenoids, sterol profile responded to the sugar present in the medium, β-sitosterol dominating in roots grown on 3% or lower glucose concentrations and stigmasterol in 3% sucrose. These results indicate an involvement of sugar signaling in the regulation of cis-prenyltransferases and phytosterol pathway enzymes.     

Polyprenyl lipid synthesis in mammalian cells expressing human cis-prenyl transferase

The level of cis-prenyl transferase activity has been implicated in controlling the level of biosynthesis of dolichol and dolichol intermediates. In this study, we isolated a cDNA encoding a human CPT (GenBank Accession No. ), which had substantial homology to other CPT isolated from human brain, bacteria, Arabidopsis, and Saccharomyces cerevisiae. Expression of this cDNA in two different insect cell lines confirmed the functionality of the protein in an in vitro assay. Western blot analysis revealed an expressed protein of approximately 38 kDa in HEK293 cells. Overexpression of the protein in HEK293 cells resulted in an increase in the level of total prenol in vivo. Furthermore, product characterization by thin layer chromatography (TLC) confirmed that the major product was a long-chain prenol with a chain length of 95 carbons. These results suggest a regulatory relationship between CPT activity and dolichol biosynthesis, and may implicate CPT in the levels of dolichol-oligosaccharide intermediate biosynthesis.     

Synthesis of 2-deoxy-2-fluoro analogs of polyprenyl beta-D-arabinofuranosyl phosphates

Described is the synthesis of polyprenyl 2-deoxy-2-fluoro-beta-D-arabinofuranosyl phosphate derivatives, including an analog of decaprenyl beta-D-arabinofuranosyl phosphate, the donor species used by the arabinosyltransferases involved in mycobacterial cell-wall biosynthesis. The targets were synthesized via a route involving the synthesis of a protected beta-D-arabinofuranosyl phosphate derivative, its coupling with a polyprenyl trichloroacetimidate, and then deprotection of the resulting product. The use of arabinofuranosyl phosphates with the monosaccharide hydroxyl groups protected as either silyl ethers or benzoate esters was explored. Although the coupling yields between the phosphate and polyprenyl trichloroacetimidates were comparable with either type of protecting group, access to the benzoyl-protected derivative was more efficient and therefore gave the products in higher overall yield.     

Alloprenols: novel alpha-trans-polyprenols of Allophylus caudatus

A novel type of polyprenols, alloprenols, with an α-trans-isoprenoid unit was found in the leaves of Allophylus caudatus (Sapindaceae) besides typical α-cis-polyprenols. The polyprenol family (Prenol-11-13, Prenol-12 dominating) was accompanied by traces of dolichols of the same chain-length. Prenol α-cis- and α-trans-isomers were chromatographically separated and their structure was analyzed by HPLC/ESI-MS, HR-ESI-MS and ¹H and ¹³C NMR spectroscopy. Model compounds, semi-synthetic α-isomers of all-trans-Pren-9 and mainly-cis-Pren-11, were obtained using an oxidation-reduction procedure. Comparison of their NMR spectra confirmed the structure of the newly identified polyprenols. The observed pattern of NMR signal shifts may be applied for elucidation of isoprenoid structure.     

The possible role of lipid intermediates in the synthesis of β-glucans by a membrane fraction from pollen tubes of Petunia hybrida

A membrane fraction, isolated from pollen tubes of Petunia hybrida, catalyses the incorporation of glucose from UDP-glucose into sucrose, cellodextrins, -glucans, sterol glucosides and polyprenol monophosphate glucose. Incorporation studies with isolated lipids and kinetic and double-labelling studies indicated that glucolipids are not intermediates in the synthesis of -glucans in this system.