title: The biosynthesis of GDP-D-arabinopyranose in Crithidia fasciculata: characterization of a D-arabino-1-kinase activity and its use in the synthesis of GDP-[5-3H]D-arabinopyranose.
abstract: GDP-D-arabinopyranose (GDP-D-Ara) is the precursor of the uncommon D-arabinopyranose residues present in the glycoconjugates of a few trypanosomatid parasites. Biosynthetic labelling experiments with Crithidia fasciculata showed that GDP-D-Ara could be labelled with [3H]D-Ara, [2-3H]D-Glc and [6-3H]D-Glc, but not with [1-3H]D-Glc, suggesting that D-Ara can be either taken up directly by the parasite or derived from D-Glc through a pathway involving the loss of carbon C-1. In vivo pulse-chase experiments indicated that D-Ara was sequentially incorporated into D-Ara-1-PO4 and GDP-D-Ara prior to transfer to the acceptor glycoconjugate, lipoarabinogalactan. An MgATP-dependent D-arabino-1-kinase activity present in soluble extracts of C. fasciculata was purified away from phosphatase activities by size-exclusion chromatography. The D-arabino-1-kinase had an apparent molecular mass of 600 kDa, a neutral optimum pH, and displayed substrate inhibition at D-Ara concentrations above 100 microM. It had a KmATP of 1.7 mM and a KmAra of 24 microM. Competition studies indicated that the orientation of every single hydroxyl residue was important for D-Ara recognition by the enzyme, but that methyl or hydroxymethyl groups could be tolerated as equatorial substituents on C-5 of D-Ara. The partially purified D-arabino-1-kinase activity was used in the chemico-enzymic synthesis of GDP-[5-3H]D-Ara from [6-3H]D-GlcN.
authors.affiliation: Department of Biochemistry, University of Dundee, UK.
authors.forename: P
authors.initials: P
authors.lastname: Schneider
authors.forename: A
authors.initials: A
authors.lastname: Nikolaev
authors.forename: M A
authors.initials: MA
authors.lastname: Ferguson
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D016831:Crithidia fasciculata / Q000201:enzymology*; D005685:Galactans / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D017261:Glycosylphosphatidylinositols / Q000378:metabolism; D006156:Guanosine Diphosphate Sugars / Q000096:biosynthesis*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008970:Molecular Weight; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D013379:Substrate Specificity; D014316:Tritium
chemical_list: D005685:Galactans; D017261:Glycosylphosphatidylinositols; D006156:Guanosine Diphosphate Sugars; D014316:Tritium; C088421:guanidine diphosphate-arabinopyranose; D000255:Adenosine Triphosphate; C095989:D-arabino-1-kinase; D017853:Phosphotransferases (Alcohol Group Acceptor); D005947:Glucose; C005653:arabinogalactan