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)

L-Fucose and N-acetylneuraminic (sialic) acid occupy terminal positions on the oligosaccharide side-chains of human cervical mucin but the addition of both these monosaccharides to the same carbohydrate acceptor residue is kinetically unfavourable. The following evidence suggests that the levels of L-fucose are more sensitive to regulation than those of N-acetylneuraminic acid: (1) tissue levels of sialyltransferase (EC 2.4.99.1) activity are 20-30 times greater than those of fucosyltransferase (EC 2.4.1.68); (2) both glycosyltransferases are susceptible to inhibition by their nucleotide products but a comparison of the Ki and the apparent Km of these enzymes shows that modulation of fucosyltransferase is more probable; (3) Postsecretory removal of L-fucose from cervical mucin is probably due to the high levels of mucus-associated alpha-L-fucosidase. Furthermore the activity of this enzyme is probably modulated by the pH gradient within the cervix. Mucin glycosylation can be visualized by autoradiography using [3H]L-fucose applied to cervical explants in organ culture. Mucus production during this process is not sensitive to exogenous ovarian steroid hormones, though in other aspects the secretory process appears normal. It is proposed that the cyclicity of mucus rheology is not directly influenced by an action of these hormones on mucin synthesis or hydration.
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PMID:Terminal glycosylation in human cervical mucin. 656 36

Mucin type O-glycans with core 2 branches are distinct from nonbranched O-glycans, and the amount of core 2 branched O-glycans changes dramatically during T cell differentiation. This oligosaccharide is synthesized only when core 2 beta-1, 6-N-acetylglucosaminyltransferase (C2GnT) is present, and the expression of this glycosyltransferase is highly regulated. To understand how O-glycan synthesis is regulated by the orderly appearance of glycosyltransferases that form core 2 branched O-glycans, the subcellular localization of C2GnT was determined by using antibodies generated that are specific to C2GnT. The studies using confocal light microscopy demonstrated that C2GnT was localized mainly in cis to medial-cisternae of the Golgi. We then converted C2GnT to a trans-Golgi enzyme by replacing its Golgi retention signal with that of alpha-2,6-sialyltransferase, which resides in trans-Golgi. Chinese hamster ovary cells expressing wild type C2GnT and the chimeric C2GnT were then subjected to oligosaccharide analysis. The results obtained clearly indicate that the conversion of C2GnT into a trans-Golgi enzyme resulted in a substantial decrease of core 2 branched oligosaccharides. These results, taken together, strongly suggest that the predominance of core 2 branched oligosaccharides in those cells expressing C2GnT is due to the fact that C2GnT is located earlier in the Golgi than alpha-2,3-sialyltransferase that competes with C2GnT for the common substrate. Furthermore, alteration of Golgi localization renders the chimeric C2GnT much less efficient in synthesizing core 2 branched oligosaccharides, indicating the critical role of orderly subcellular localization of glycosyltransferases.
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PMID:Altered Golgi localization of core 2 beta-1,6-N-acetylglucosaminyltransferase leads to decreased synthesis of branched O-glycans. 927 27