title: 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.
abstract: 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.
authors.affiliation: Department of Horticulture, the University of Adelaide, Waite Campus PMB1, Glen Osmond SA 5064, South Australia, Australia.
authors.forename: P R
authors.initials: PR
authors.lastname: Jones
authors.forename: B L
authors.initials: BL
authors.lastname: Moller
authors.forename: P B
authors.initials: PB
authors.lastname: Hoj
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D002523:Edible Grain / Q000201:enzymology* / Q000235:genetics; D005964:Glucosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009570:Nitriles / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D003313:Zea mays / Q000201:enzymology
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D009570:Nitriles; D011994:Recombinant Proteins; D005964:Glucosyltransferases; C402689:cyanohydrin beta-glucosyltransferase; C011220:dhurrin