Investigation on determinants of substrate specificities of nucleotide-sugar transporters

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Nucleotide sugar transporters are very hydrophobic proteins ranging from 340 a.a. to 400 a.a. long. They reside in Golgi apparatus and/or ER membrane exposing their C- and N-terminal regions to cytosol, and are highly likely to have ten transmembrane helices. They antiport nucleotide sugars pooled in cytosol into lumen of Golgi apparatus and/or ER lumen with the corresponding nucleoside monophosphates. The transported nucleotide sugars are utilized as sugar donors by glycosyltransferases for synthesis of sugar chains of glycoproteins. glycolipids and polysaccharides.Nucleotide-sugar transporter genes constitute a gene family that was assigned as SLC (solute carrier)35 family by the HUGO gene nomenclature committee. We carried out data mining of the gene databank, and found 23 human genes which shows significant similarity each others. We classified them into 6 subfamilies, from A to F, based on their similarity, and provided the gene symbol to each of the genes.We had found hUGTrel8 (S … More LC35D2) gene that exhibits around 50% similarity with human SLC35D1 (UDP-glucuronic acid/UDP-N-acetylgalactosamine transporter), fruitfly fringe connection (frc) transporter, and nematode SQV-7 transporter, the latter two being involved in developmental and ontological processes. We demonstrated that SLC35D2 was localized in the Golgi apparatus and transported UDP-N-acetylglucosamine. These observations indicate that SLC35D2 is a good candidate for the ortholog of frc transporter.We also biochemically demonstrated that a Drosophila homolog of the human GDP-fucose transporter, the Golgi GDP-fucose transporter (Gfr), specifically transport GDP-fucose in vitro, and generated null mutants of Gfr in Drosophila. The phenotypes of the Drosophila Gfr mutants were rescued by the human GDP-fucose transporters. Hence, these null mutants are good Drosophila models of CDGIIc patients who have defective GDP-fucose transporter to investigate the possible cause of the developmental defects in the patients. Less