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)

Cobra venom factor (CVF) is the nontoxic C-activating glycoprotein in cobra venom. It is a structural and functional analogue of complement component C3. Previous work has established that the major oligosaccharide chain of CVF is a symmetric fucosylated biantennary complex-type N-linked chain containing an alpha-galactosylated Le(x) antigenic epitope, Gal alpha 1-3Gal beta 1-4 (Fuc alpha 1-3) GlcNAc beta 1, a novel carbohydrate structure. We show that naturally occurring anti-alpha-Gal Ab present in normal human serum binds to CVF. In view of a possible human application of CVF, we studied the effect of this anti-alpha-Gal Ab on CVF function as well as the effect of oligosaccharide modification or removal on CVF activity and immunoreactivity with the anti-alpha-Gal Ab. The immunoreactivity of CVF with the anti-alpha-Gal Ab is abolished upon de-alpha-galactosylation or complete deglycosylation. De-alpha-galactosylated CVF and deglycosylated CVF were found to be equally active in forming a stable C3/C5 convertase with human factor B and in decomplementing human serum indicating that the oligosaccharide chains of CVF are not required for its C-activating function. Consistent with the unaltered functional activity, deglycosylation of the molecule caused only minor changes in secondary structure as judged by far UV circular dichroism analysis. However, the oligosaccharide chains appear to contribute to the thermal stability of CVF, because deglycosylation caused the molecule to be more sensitive to temperature. Inasmuch as rCVF produced in mammalian cells can be expected to contain sialylated oligosaccharide chains, we also prepared sialylated CVF by enzymatic sialylation of de-alpha-galactosylated and de-alpha-fucosylated CVF with 2,6-sialyltransferase. It was found that the secondary structure and the activity of sialylated CVF were unchanged compared to native CVF.
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PMID:Immunoreactivity and function of oligosaccharides in cobra venom factor. 814 97

Previous studies indicate that sialylation of lipopolysaccharide (LPS) by host CMP-N-acetylneuraminic acid (CMP-NANA) catalyzed by bacterial sialyltransferase rendered gonococci resistant to killing by phagocytes, to entry into epithelial cell lines, to killing by immune serum and complement, and to absorption of complement component C3. These results have been confirmed by comparing a sialyltransferase-deficient mutant (strain JB1) with its parent (strain F62) in appropriate tests. In contrast to F62, JB1 was very susceptible to killing by human polymorphonuclear phagocytes in opsonophagocytosis tests and incubation with CMP-NANA did not decrease the level of killing. The inherent resistance of F62 in these tests was probably due to LPS sialylation by CMP-NANA and lactate present in the phagocytes. A JB1 variant expressing the invasion-associated Opa protein was as able to enter Chang human conjunctiva epithelial cells as an Opa-positive variant of F62, suggesting that the sialyltransferase is not required for Opa-mediated entry. After incubation with CMP-NANA, the number of F62 variant gonococci entering cells but not that of JB1 variant gonococci was drastically reduced. Both JB1 and F62 were killed by incubation with rabbit antibody to gonococcal major outer membrane protein, protein I, and human complement, but only F62 was rendered resistant to the killing by incubation with CMP-NANA. Finally, both JB1 and F62 absorbed similar amounts of complement component C3 and the binding was decreased by incubation with CMP-NANA only for the wild type, F62.
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PMID:Functional characterization of a sialyltransferase-deficient mutant of Neisseria gonorrhoeae. 875 78