title: Characterization of AtNST-KT1, a novel UDP-galactose transporter from Arabidopsis thaliana.
abstract: Nucleotide sugar transporters (NST) mediate the transfer of nucleotide sugars from the cytosol into the lumen of the endoplasmatic reticulum and the Golgi apparatus. Because the NSTs show similarities with the plastidic phosphate translocators (pPTs), these proteins were grouped into the TPT/NST superfamily. In this study, a member of the NST-KT family, AtNST-KT1, was functionally characterized by expression of the corresponding cDNA in yeast cells and subsequent transport experiments. The histidine-tagged protein was purified by affinity chromatography and reconstituted into proteoliposomes. The substrate specificity of AtNST-KT1 was determined by measuring the import of radiolabelled nucleotide mono phosphates into liposomes preloaded with various unlabelled nucleotide sugars. This approach has the advantage that only one substrate has to be used in a radioactively labelled form while all the nucleotide sugars can be provided unlabelled. It turned out that AtNST-KT1 represents a monospecific NST transporting UMP in counterexchange with UDP-Gal but did not transport other nucleotide sugars. The AtNST-KT1 gene is ubiquitously expressed in all tissues. AtNST-KT1 is localized to Golgi membranes. Thus, AtNST-KT1 is most probably involved in the synthesis of galactose-containing glyco-conjugates in plants.
authors.affiliation: Botanisches Institut, Universität zu Köln, Gyrhofstrasse 15, 50931 Köln, Germany.
authors.forename: Inga
authors.initials: I
authors.lastname: Rollwitz
authors.forename: Marcella
authors.initials: M
authors.lastname: Santaella
authors.forename: Diana
authors.initials: D
authors.lastname: Hille
authors.forename: Ulf-Ingo
authors.initials: UI
authors.lastname: Flügge
authors.forename: Karsten
authors.initials: K
authors.lastname: Fischer
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D006056:Golgi Apparatus / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D013379:Substrate Specificity; D000099237:UDP-Galactose Translocators
chemical_list: D029681:Arabidopsis Proteins; D009004:Monosaccharide Transport Proteins; D000099237:UDP-Galactose Translocators