Publications

• Metabolic engineering of dhurrin in transgenic Arabidopsis plants with marginal inadvertent effects on the metabolome and transcriptome.

  Kristensen C., Morant M., Olsen C.E., Ekstroem C.T., Galbraith D.W., Moeller B.L., Bak S.

  Focused and nontargeted approaches were used to assess the impact associated with introduction of new high-flux pathways in Arabidopsis thaliana by genetic engineering. Transgenic A. thaliana plants expressing the entire biosynthetic pathway for the tyrosine-derived cyanogenic glucoside dhurrin as ... >> More

  Focused and nontargeted approaches were used to assess the impact associated with introduction of new high-flux pathways in Arabidopsis thaliana by genetic engineering. Transgenic A. thaliana plants expressing the entire biosynthetic pathway for the tyrosine-derived cyanogenic glucoside dhurrin as accomplished by insertion of CYP79A1, CYP71E1, and UGT85B1 from Sorghum bicolor were shown to accumulate 4% dry-weight dhurrin with marginal inadvertent effects on plant morphology, free amino acid pools, transcriptome, and metabolome. In a similar manner, plants expressing only CYP79A1 accumulated 3% dry weight of the tyrosine-derived glucosinolate, p-hydroxybenzylglucosinolate with no morphological pleitropic effects. In contrast, insertion of CYP79A1 plus CYP71E1 resulted in stunted plants, transcriptome alterations, accumulation of numerous glucosides derived from detoxification of intermediates in the dhurrin pathway, and in loss of the brassicaceae-specific UV protectants sinapoyl glucose and sinapoyl malate and kaempferol glucosides. The accumulation of glucosides in the plants expressing CYP79A1 and CYP71E1 was not accompanied by induction of glycosyltransferases, demonstrating that plants are constantly prepared to detoxify xenobiotics. The pleiotrophic effects observed in plants expressing sorghum CYP79A1 and CYP71E1 were complemented by retransformation with S. bicolor UGT85B. These results demonstrate that insertion of high-flux pathways directing synthesis and intracellular storage of high amounts of a cyanogenic glucoside or a glucosinolate is achievable in transgenic A. thaliana plants with marginal inadvertent effects on the transcriptome and metabolome. << Less

  Proc. Natl. Acad. Sci. U.S.A. 102:1779-1784(2005) [PubMed] [EuropePMC]

  This publication is cited by 7 other entries.

• Determination of catalytic key amino acids and UDP sugar donor specificity of the cyanohydrin glycosyltransferase UGT85B1 from Sorghum bicolor. Molecular modeling substantiated by site-specific mutagenesis and biochemical analyses.

  Thorsoee K.S., Bak S., Olsen C.E., Imberty A., Breton C., Moeller B.L.

  Plants produce a plethora of structurally diverse natural products. The final step in their biosynthesis is often a glycosylation step catalyzed by a family 1 glycosyltransferase (GT). In biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor, the UDP-glucosyltransferase UGT85B1 catal ... >> More

  Plants produce a plethora of structurally diverse natural products. The final step in their biosynthesis is often a glycosylation step catalyzed by a family 1 glycosyltransferase (GT). In biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor, the UDP-glucosyltransferase UGT85B1 catalyzes the conversion of p-hydroxymandelonitrile into dhurrin. A structural model of UGT85B1 was built based on hydrophobic cluster analysis and the crystal structures of two bacterial GTs, GtfA and GtfB, which each showed approximately 15% overall amino acid sequence identity to UGT85B1. The model enabled predictions about amino acid residues important for catalysis and sugar donor specificity. p-Hydroxymandelonitrile and UDP-glucose (Glc) were predicted to be positioned within hydrogen-bonding distance to a glutamic acid residue in position 410 facilitating sugar transfer. The acceptor was packed within van der Waals distance to histidine H23. Serine S391 and arginine R201 form hydrogen bonds to the pyrophosphate part of UDP-Glc and hence stabilize binding of the sugar donor. Docking of UDP sugars predicted that UDP-Glc would serve as the sole donor sugar in UGT85B1. This was substantiated by biochemical analyses. The predictive power of the model was validated by site-directed mutagenesis of selected residues and using enzyme assays. The modeling approach has provided a tool to design GTs with new desired substrate specificities for use in biotechnological applications. The modeling identified a hypervariable loop (amino acid residues 156-188) that contained a hydrophobic patch. The involvement of this loop in mediating binding of UGT85B1 to cytochromes P450, CYP79A1, and CYP71E1 within a dhurrin metabolon is discussed. << Less

  Plant Physiol. 139:664-673(2005) [PubMed] [EuropePMC]

• The in vitro substrate regiospecificity of recombinant UGT85B1, the cyanohydrin glucosyltransferase from Sorghum bicolor.

  Hansen K.S., Kristensen C., Tattersall D.B., Jones P.R., Olsen C.E., Bak S., Moeller B.L.

  The in vitro substrate specificity of UDP-glucose:p-hydroxymandelonitrile-O-glucosyltransferase from Sorghum bicolor (UGT85B1) was examined using a range of potential acceptor molecules, including cyanohydrins, terpenoids, phenolics, hexanol derivatives and plant hormones. Qualitative enzyme activ ... >> More

  The in vitro substrate specificity of UDP-glucose:p-hydroxymandelonitrile-O-glucosyltransferase from Sorghum bicolor (UGT85B1) was examined using a range of potential acceptor molecules, including cyanohydrins, terpenoids, phenolics, hexanol derivatives and plant hormones. Qualitative enzyme activity assays employing 20 different putative substrates were performed and 15 proved to be glucosylated using recombinant UGT85B1 isolated from Escherichia coli. K(m) and k(cat) values were determined for nine of these substrates including mandelonitrile, geraniol, nerol and beta-citronellol, 2-hydroxy-3-methoxybenzyl alcohol, 1-hexanol, cis-3-hexen-1-ol, 3-methyl-3-buten-1-ol and 3-methyl-2-buten-1-ol. UGT85B1 has a rather broad substrate specificity in vitro but shows regiospecificity, demanding the presence of a sterically unhindered hydroxyl group e.g. as part of a cyanohydrin function, as a primary alcohol or as a phenolic hydroxyl group and being influenced by the stereochemistry and/or interactive chemistry of the substituents on the hydroxyl-bearing carbon atom. << Less

  Phytochemistry 64:143-151(2003) [PubMed] [EuropePMC]

• Dhurrin synthesis in sorghum is regulated at the transcriptional level and induced by nitrogen fertilization in older plants.

  Busk P.K., Moller B.L.

  The content of the cyanogenic glucoside dhurrin in sorghum (Sorghum bicolor L. Moench) varies depending on plant age and growth conditions. The cyanide potential is highest shortly after onset of germination. At this stage, nitrogen application has no effect on dhurrin content, whereas in older pl ... >> More

  The content of the cyanogenic glucoside dhurrin in sorghum (Sorghum bicolor L. Moench) varies depending on plant age and growth conditions. The cyanide potential is highest shortly after onset of germination. At this stage, nitrogen application has no effect on dhurrin content, whereas in older plants, nitrogen application induces an increase. At all stages, the content of dhurrin correlates well with the activity of the two biosynthetic enzymes, CYP79A1 and CYP71E1, and with the protein and mRNA level for the two enzymes. During development, the activity of CYP79A1 is lower than the activity of CYP71E1, suggesting that CYP79A1 catalyzes the rate-limiting step in dhurrin synthesis as has previously been shown using etiolated seedlings. The site of dhurrin synthesis shifts from leaves to stem during plant development. In combination, the results demonstrate that dhurrin content in sorghum is largely determined by transcriptional regulation of the biosynthetic enzymes CYP79A1 and CYP71E1. << Less

  Plant Physiol 129:1222-1231(2002) [PubMed] [EuropePMC]

  This publication is cited by 5 other entries.

• The UDP-glucose:p-hydroxymandelonitrile-O-glucosyltransferase that catalyzes the last step in synthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor. Isolation, cloning, heterologous expression, and substrate specificity.

  Jones P.R., Moeller B.L., Hoej P.B.

  The final step in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor is the transformation of the labile cyanohydrin into a stable storage form by O-glucosylation of (S)-p-hydroxymandelonitrile at the cyanohydrin function. The UDP-glucose:p-hydroxymandelonitrile-O-glucosyltran ... >> More

  The final step in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor is the transformation of the labile cyanohydrin into a stable storage form by O-glucosylation of (S)-p-hydroxymandelonitrile at the cyanohydrin function. The UDP-glucose:p-hydroxymandelonitrile-O-glucosyltransferase was isolated from etiolated seedlings of S. bicolor employing Reactive Yellow 3 chromatography with UDP-glucose elution as the critical step. Amino acid sequencing allowed the cloning of a full-length cDNA encoding the glucosyltransferase. Among the few characterized glucosyltransferases, the deduced translation product showed highest overall identity to Zea mays flavonoid-glucosyltransferase (Bz-Mc-2 allele). The substrate specificity of the enzyme was established using isolated recombinant protein. Compared with endogenous p-hydroxymandelonitrile, mandelonitrile, benzyl alcohol, and benzoic acid were utilized at maximum rates of 78, 13, and 4%, respectively. Surprisingly, the monoterpenoid geraniol was glucosylated at a maximum rate of 11% compared with p-hydroxymandelonitrile. The picture that is emerging regarding plant glucosyltransferase substrate specificity is one of limited but extended plasticity toward metabolites of related structure. This in turn ensures that a relatively high, but finite, number of glucosyltransferases can give rise to the large number of glucosides found in plants. << Less

  J. Biol. Chem. 274:35483-35491(1999) [PubMed] [EuropePMC]