Publications

• Molecular cloning and characterization of one member of 3beta-hydroxy sterol glucosyltransferase gene family in Withania somnifera.

  Sharma L.K., Madina B.R., Chaturvedi P., Sangwan R.S., Tuli R.

  Sterol glycosides are constituents of plant cell membranes. Glucosylations of the sterols are catalyzed by sterol glucosyltransferases (SGTs), which are members of family 1 glycosyltransferases. We have identified the family of SGT genes expressed in the leaves of a medicinal plant Withania somnif ... >> More

  Sterol glycosides are constituents of plant cell membranes. Glucosylations of the sterols are catalyzed by sterol glucosyltransferases (SGTs), which are members of family 1 glycosyltransferases. We have identified the family of SGT genes expressed in the leaves of a medicinal plant Withania somnifera. One member (SGTL1) of this gene family was cloned. The full-length cDNA sequence of SGTL1 represents 2532 bp, comprising untranslated regions (UTRs) of 337 and 89 bp at the 5' and 3' ends, respectively. The amino acid sequence deduced from the 2103 bp open reading frame (ORF) showed homology (67-45%) to the reported plant SGTs. The presence of two putative transmembrane domains suggested the association of SGTL1 with membrane. The SGTL1 was expressed in Escherichia coli and recombinant enzyme from the supernatant was partially purified and biochemically characterized. The relative activity and kinetic properties of SGTL1 for different sterols were compared with a recombinant SGT (GenBank Accession No. Z83833) of Arabidopsis thaliana (AtSGT). Both the recombinant enzymes showed activity with 3-beta-OH sterols. The distribution of SGTL1 transcript in W. somnifera, as determined by quantitative PCR, showed higher expression in roots and mature leaves. Expression of the SGTL1 transcript in the leaves of W. somnifera was enhanced following the application of salicylic acid. In contrast, it decreased rapidly on exposure of the plants to heat shock, suggesting functional role of the enzyme in biotic and abiotic stresses. << Less

  Arch Biochem Biophys 460:48-55(2007) [PubMed] [EuropePMC]

  This publication is cited by 10 other entries.

• Tomato UDP-Glucose Sterol Glycosyltransferases: A Family of Developmental and Stress Regulated Genes that Encode Cytosolic and Membrane-Associated Forms of the Enzyme.

  Ramirez-Estrada K., Castillo N., Lara J.A., Arro M., Boronat A., Ferrer A., Altabella T.

  Sterol glycosyltransferases (SGTs) catalyze the glycosylation of the free hydroxyl group at C-3 position of sterols to produce sterol glycosides. Glycosylated sterols and free sterols are primarily located in cell membranes where in combination with other membrane-bound lipids play a key role in m ... >> More

  Sterol glycosyltransferases (SGTs) catalyze the glycosylation of the free hydroxyl group at C-3 position of sterols to produce sterol glycosides. Glycosylated sterols and free sterols are primarily located in cell membranes where in combination with other membrane-bound lipids play a key role in modulating their properties and functioning. In contrast to most plant species, those of the genus <i>Solanum</i> contain very high levels of glycosylated sterols, which in the case of tomato may account for more than 85% of the total sterol content. In this study, we report the identification and functional characterization of the four members of the tomato (<i>Solanum lycopersicum</i> cv. Micro-Tom) <i>SGT</i> gene family. Expression of recombinant SlSGT proteins in <i>E. coli</i> cells and <i>N. benthamiana</i> leaves demonstrated the ability of the four enzymes to glycosylate different sterol species including cholesterol, brassicasterol, campesterol, stigmasterol, and β-sitosterol, which is consistent with the occurrence in their primary structure of the putative steroid-binding domain found in steroid UDP-glucuronosyltransferases and the UDP-sugar binding domain characteristic for a superfamily of nucleoside diphosphosugar glycosyltransferases. Subcellular localization studies based on fluorescence recovery after photobleaching and cell fractionation analyses revealed that the four tomato SGTs, like the Arabidopsis SGTs UGT80A2 and UGT80B1, localize into the cytosol and the PM, although there are clear differences in their relative distribution between these two cell fractions. The <i>SlSGT</i> genes have specialized but still largely overlapping expression patterns in different organs of tomato plants and throughout the different stages of fruit development and ripening. Moreover, they are differentially regulated in response to biotic and abiotic stress conditions. <i>SlSGT4</i> expression increases markedly in response to osmotic, salt, and cold stress, as well as upon treatment with abscisic acid and methyl jasmonate. Stress-induced <i>SlSGT2</i> expression largely parallels that of <i>SlSGT4</i>. On the contrary, <i>SlSGT1</i> and <i>SlSGT3</i> expression remains almost unaltered under the tested stress conditions. Overall, this study contributes to broaden the current knowledge on plant SGTs and provides support to the view that tomato SGTs play overlapping but not completely redundant biological functions involved in mediating developmental and stress responses. << Less

  Front Plant Sci 8:984-984(2017) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• Purification and physico-kinetic characterization of 3beta-hydroxy specific sterol glucosyltransferase from Withania somnifera (L) and its stress response.

  Madina B.R., Sharma L.K., Chaturvedi P., Sangwan R.S., Tuli R.

  Sterol glycosyltransferases catalyze the synthesis of diverse glycosteroids in plants, leading to a change in their participation in cellular metabolism. Withania somnifera is a medically important plant, known for a variety of pharmacologically important withanolides and their glycosides. In this ... >> More

  Sterol glycosyltransferases catalyze the synthesis of diverse glycosteroids in plants, leading to a change in their participation in cellular metabolism. Withania somnifera is a medically important plant, known for a variety of pharmacologically important withanolides and their glycosides. In this study, a cytosolic sterol glucosyltransferase was purified 3406 fold to near homogeneity from W. somnifera leaves and studied for its biochemical and kinetic properties. The purified enzyme was active with UDP-glucose but not with UDP-galactose as sugar donor. It exhibited broad sterol specificity by glucosylating a variety of sterols and phytosterols with 3beta-OH group. It showed a low level of activity with flavonoids and isoflavonoids. The enzyme gave maximum K(cat)/K(m) value (0.957) for 24-methylenecholesterol that resembles aglycone structure of pharmacologically important sitoindosides VII and VIII from W. somnifera. The enzyme follows ordered sequential bisubstrate mechanism of reaction, in which UDP-glucose and sterol are the first and second binding substrates. This is the first detailed kinetic study on purified plant cytosolic sterol glucosyltransferases. Results on peptide mass fingerprinting and substrate specificity suggested that the enzyme belongs to the family of secondary metabolite glucosylating glucosyltransferases. The enzyme activity exhibited a rapid in vivo response to high temperature and salicylic acid treatment of plants, suggesting its physiological role in abiotic and biotic stress. << Less

  Biochim Biophys Acta 1774:392-402(2007) [PubMed] [EuropePMC]

  This publication is cited by 9 other entries.