5 research outputs found
SIALYLTRANSFERASES; THEIR SPECIFICITY AND THEIR USE IN CARBOHYDRATE REMODELLING.
In order to apply sialyltransferases in the remodelling of the
carbohydrate chains on biologically active glycoproteins, it is a
prerequisite to know the fine specificity of these enzymes. In this
report the specificity of several sialyltransferses involved in the
sialylation of O- and N-linked oligosaccharide chains is reviewed.
Also novel results on the branch specificity of a3- and a6-sialyltransferase
are reported.
The potential application of these enzymes in carbohydrate
remodelling was studied using human chorionic gonadotropin (hCG) as a
model glycoprotein. Differently sialylated preparations of this
hormone were obtained and tested for their stimulatory effect on
steroidogenesis in Leydig cells in vitro. Asialo-hCcG appeared to be
only 45% as effective as native hCG. a3-Resialylation of the O-linked
chains on the ß-subunit of this hormone did not restore the
biological activity to a higher level. By contrast, 55% a6-
resialylation of the N-linked chains yielded a preparation which was
almost as active as native hCG. Interestingly, further sialylation by
the a6-sialyltransferase resulted in a decrease of the bio-activity
to levels lower than obtained with asialo-hcG.
It is concluded that the lectin-carbohydrate binding, which is
part of the process that triggers the biological respons of the
target cell can be mimicked by N-linked chains carrying a6-linked
sialic acid. However, too high a density of such residues interferes
with this interaction
Porcine submaxillary mucin contains alpha23- and alpha26-linked n-acetyl- and n-glycolyl-neuraminic acid
LacdiNAc-glycans constitute a parasite pattern for galectin-3-mediated immune recognition
Although Gal beta 1-4GlcNAc (LacNAc) moieties are the most common constituents of N-linked glycans on vertebrate proteins, GalNAc beta 1-4GlcNAc (LacdiNAc, LDN)-containing glycans are widespread in invertebrates, such as helminths. We postulated that LDN might be a molecular pattern for recognition of helminth parasites by the immune system. Using LDN-based affinity chromatography and mass spectrometry, we have identified galectin-3 as the major LDN-binding protein in macrophages. By contrast, LDN binding was not observed with galectin-1. Surface plasmon resonance (SPR) analysis and a solid phase binding assay demonstrated that galectin-3 binds directly to neoglycoconjugates carrying LDN glycans. In addition, galectin-3 bound to Schistosoma mansoni soluble egg Ags and a mAb against the LDN glycan inhibited this binding, suggesting that LDN glycans within S. mansoni soluble egg Ags contribute to galectin-3 binding. Immunocytochemistry demonstrated high levels of galectin-3 in liver granulomas of S. mansoni-infected hamsters, and a colocalization of galectin-3 and LDN glycans was observed on the parasite eggshells. Finally, we demonstrate that galectin-3 can mediate recognition and phagocytosis of LDN-coated particles by macrophages. These findings provide evidence that LDN-glycans constitute a parasite pattern for galectin-3-mediated immune recognitio