Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.99.7 (sialyltransferase)
 1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cytoplasmic droplet of epididymal spermatozoa is a small localized outpouching of cytoplasm of the tail of unknown significance. EM revealed flattened saccular elements as the near exclusive membranous component of the droplet. Light and electron microscopic immunolabeling for Golgi/TGN markers showed these saccules to be reactive for antibodies to TGN38, protein affinity-purified alpha 2,6 sialyltransferase, and anti-human beta 1,4 galactosyltransferase. The saccules were isolated by subcellular fractionation and antibodies raised against this fraction immunolabeled the saccules of the droplet in situ as well as the Golgi region of somatic epithelial cells lining the epididymis. The isolated droplet fraction was enriched in galactosyltransferase and sialyltransferase activities, and endogenous glycosylation assays identified the modification of several endogenous glycopeptides. EM lectin staining in situ demonstrated galactose and N-acetyl galactosamine constituents in the saccules. Endocytic studies with cationic and anionic ferritin as well as HRP failed to identify the saccules as components of the endocytic apparatus. Epididymal spermatozoa were devoid of markers for the ER as well as the Golgi-associated coatamer protein beta-COP. It is therefore unlikely that the saccular elements of the droplet participate in vesicular protein transport. However, the identification of Golgi/TGN glycosylating activities in the saccules may be related to plasma membrane modifications which occur during epididymal sperm maturation.
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PMID:The cytoplasmic droplet of rat epididymal spermatozoa contains saccular elements with Golgi characteristics. 822 42

Spermatozoa acquire fertilizing ability during passage through the epididymis. Modification of oligosaccharide moieties on sperm surface glycoproteins are some of the biochemical changes believed to be important in the production of functionally mature spermatozoa during passage through the epididymis. In an attempt to understand the mechanism underlying these modifications, we quantified four glycosyltransferase activities (the enzymes that catalyze the transfer of sugar residues from nucleotide sugar donor to the sugar chains on glycoproteins and glycolipids) of spermatozoa and fluid from various regions of the epididymis. Our results are as follows. (1) Only 10-20% of the total glycosyltransferase activities (sialyltransferase, fucosyltransferase, galactosyltransferase, and N-acetyl glucosaminyltransferase) sedimented with the spermatozoa; the remaining 80-90% of the four enzymes were present in soluble form in the epididymal fluid. (2) When the four transferase activities were expressed per 10(6) spermatozoa, only sialyltransferase and fucosyltransferase activities showed maturation-dependent changes. The former enzyme was significantly higher on the proximal caput spermatozoa and the latter on the distal caput spermatozoa. The higher levels of the two enzymes on caput spermatozoa could be due to their binding to the endogenous sugar acceptor molecules on the sperm surface, and subsequent release following sequential sialylation and fucosylation of the molecules in the proximal and distal caput spermatozoa, respectively. (3) When spermatozoa from the proximal and distal caput, corpus, and proximal and distal cauda were incubated with fucose-labeled nucleotide sugar (GDP[14C]fucose), higher levels of radioactivity were routinely incorporated into the spermatozoa from the distal caput. (4) The [14C]fucose-labeled spermatozoa or sperm plasma membranes, when solubilized, resolved on SDS-PAGE, and visualized by autoradiography, showed that the radioactivity had been incorporated into an endogenous acceptor of 86 kDa (major component) and several minor components. Treatment of the solubilized spermatozoa with N-glycanase suggested that the [14C]fucose is mainly present on N-linked oligosaccharide units. These studies demonstrate that some of the sperm surface components are fucosylated during sperm maturation. The potential significance of the in vitro fucosylation of sperm surface components in the production of functionally mature spermatozoa is discussed.
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PMID:Glycosylation of rat sperm plasma membrane during epididymal maturation. 843 31

A molecular screen for a mouse homologue of a Drosophila carbohydrate binding protein, called Gliolectin, yielded a cDNA encoding mST3GalV/GM3 synthase (CMP-NeuAc: lactosylceramide alpha2, 3-sialyltransferase). By in situ hybridization and immunohistochemistry, mST3GalV exhibits differential expression in neural and non-neural tissues. Although expressed by all neurons in the central nervous system, neuronal populations that contribute their axons to myelinated efferent projections, such as cerebellar Purkinje cells and spinal motorneurons, demonstrate the highest ST3GalV expression. When stained with anti-mST3GalV antiserum (designated CS2), subpopulations of neurons display an elaborate Golgi apparatus, frequently extending into one or more dendritic processes. The extended spatial distribution of the neuronal Golgi apparatus, particularly in spinal motorneurons, allowed the confocal immunohistochemical colocalization of mST3GalV with markers for medial/trans-Golgi but not the cis-Golgi or trans-Golgi network, consistent with previous observations suggesting that ganglioside glycosyltransferases are enriched in late Golgi compartments. Among non-neural tissues, liver and testes demonstrate cell-type specific CS2 staining. In liver, endothelial cells lining a ring of sinusoids, concentric with the central vein, express mST3GalV. Kupffer cells are also stained with CS2 antiserum but hepatocyte expression is undetectable. In the seminiferous tubules of the testes, ST3GalV is found in somatic (Leydig, Sertoli) and early germline cells (spermatogonia and primary spermatocytes); the epididymal epithelium exhibits intense ST3GalV expression. Since GM3 is a precursor for the synthesis of a- and b-series gangliosides, the range of mST3GalV/GM3 synthase expression among various cell populations indicates that certain cell types possess greater reliance on ganglioside function than others.
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PMID:Molecular identification, tissue distribution and subcellular localization of mST3GalV/GM3 synthase. 1076 24