SQV-7, a protein involved in Caenorhabditis elegans epithelial invagination and early embryogenesis, transports UDP-glucuronic acid, UDP- N - acetylgalactosamine, and UDP-galactose

Abstract

Caenorhabditis elegans sqv mutants are defective in vulval epithelial invagination and have a severe reduction in hermaphrodite fertility. The gene sqv-7 encodes a multitransmembrane hydrophobic protein resembling nucleotide sugar transporters of the Golgi membrane. A Golgi vesicle enriched fraction of Saccharomyces cerevisiae expressing SQV-7 transported UDP-glucuronic acid, UDP-N-acetylgalactosamine, and UDP-galactose (Gal) in a temperature-dependent and saturable manner. These nucleotide sugars are competitive, alternate, noncooperative substrates. The two mutant sqv-7 missense alleles resulted in a severe reduction of these three transport activities. SQV-7 did not transport CMP-sialic acid, GDP-fucose, UDP-N-acetylglucosamine, UDP-glucose, or GDPmannose. SQV-7 is able to transport UDP-Gal in vivo, as shown by its ability to complement the phenotype of Madin-Darby canine kidney ricin resistant cells, a mammalian cell line deficient in UDP-Gal transport into the Golgi. These results demonstrate that unlike most nucleotide sugar transporters, SQV-7 can transport multiple distinct nucleotide sugars. We propose that SQV-7 translocates multiple nucleotide sugars into the Golgi lumen for the biosynthesis of glycoconjugates that play a pivotal role in development.M ost cell surface and secreted proteins and some lipids undergo covalent modifications by the addition of carbohydrates (1, 2). These macromolecules play essential roles in multicellular organisms by participating in normal embryonic development and cell-cell and cell-matrix interactions. The carbohydrate-deficient glycoprotein syndromes, a group of autosomal recessive multisystemic diseases characterized by defective glycosylation of N-glycans, and studies of null mutations of N-glycan biosynthetic enzymes in mice provide strong evidence that the glycan moieties of glycoproteins play essential roles in the normal development and physiology of mammals and probably of all multicellular organisms (3-5). Disorders affecting the assembly of the glycosaminoglycan moieties of proteoglycans suggest the importance of these macromolecules in connective tissue, cartilage, and bone development (3). Heparan sulfate glycosaminoglycans (GAGs) are critical components of Wingless and fibroblast growth factor signaling in Drosophila melanogaster, and defects in heparan sulfate GAG assembly are associated with effects on Drosophila embryonic development, such as abnormalities in segment-polarity cuticle patterns and in mesodermal and tracheal cell migrations (6-9). Mutations of the EXT genes, a tumor suppressor family that includes glycosyltransferases involved in polymerization of heparan sulfates, have been associated with hereditary multiple exostoses, a skeletal dysplasia characterized by multiple cartilage-capped skeletal tumors (10).Nucleotide sugar transporters translocate nucleotide sugars from the cytosol, their site of synthesis, into the lumen of the Golgi apparatus, where they are used as sugar-donor substrates by glycosyltransferases (11). Yeast, Leishmania do...

The Fine Structure of Caenorhabditis elegans N-Glycans

“…Once this system is in place, the effect that aberrant glycan biosynthesis has at the multicellular level can be more clearly understood. Such an effect has been shown by the study of the sqv mutants where metabolic error in chondroitin biosynthesis leads to malformation of the nematode vulva (5,6).…”

“…1, pools A-E) for fine structural deter-mination of major pool isomers was accomplished (Table II, Figs. [3][4][5][6][7][8].…”

Molecular Cloning and Characterization of a Human Multisubstrate Specific Nucleotide-sugar Transporter Homologous to Drosophila fringe connection

“…In Caenorhabditis elegans, sqv-7 mutants show a defect in vulva formation, with epithelial invaginations, during ontogeny (6). SQV-7 has been identified as a transporter of UDP-glucuronic acid (UDP-GlcUA), UDP-galacose (UDP-Gal), and UDP-N-acetylgalactosamine (UDP-GalNAc) (7). Biochemical analysis of sqv-7 mutants has demonstrated defects in both chondroitin and heparan sulfate biosynthesis in vivo (8).…”

The clinical relevance of glycobiology

“…These structures vary significantly between cell types and at different stages of mammalian development and probably play important roles in the interaction of a cell with its cellular and fluid environment (3)(4)(5). Glycoproteins and proteoglycans are essential for normal development in mice (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16), Drosophila melanogaster (17)(18)(19)(20), and Caenorhabditis elegans (18,(21)(22)(23)(24)(25)(26). Table 1 lists mice with null mutations in genes required for glycosylation; other null mutant mice are described in reviews by Stanley (9) and Varki and Marth (11).…”