Bovine colostrum CMP-NeuAc:Galβ(1→4)GlcNAc-R α(2→6)-sialyltransferase is involved in the synthesis of the terminal NeuAc α(2→6)GalNAcβ(1→4)GlcNAc sequence occurring on N-linked glycans of bovine milk glycoproteins

Abstract

Bovine colostrum CMP-NeuAc:Gal beta(-->4)GlcNAc-R alpha(2-->6)-sialyltransferase (alpha 6-sialyltransferase) appears to be capable of catalysing alpha 6-sialylation of the disaccharide GalNAc beta(1-->4)GlcNAc to yield the trisaccharide NeuAc alpha(2-->6)GalNAc beta(1-->4)GlcNAc. This provides an enzymic basis for the occurrence of this sialylated structure on the N-linked glycans of a number of bovine milk glycoproteins. Competition experiments using Gal beta(1-->4)GlcNAc and GalNAc beta(-->4)GlcNAc as acceptors indicate that both substrates are recognized by a single active site on the alpha 6-sialyltransferase. Extrapolation of these results suggests that the NeuAc alpha(2-->6)GalNAc beta(1-->4)GlcNAc structural element occurring on the N-linked glycans of several human glycoproteins are similarly synthesized by the action of a Gal beta(1-->4)GlcNAc-R alpha(2-->6)-sialyltransferase.

Alpha-lactalbumin affects the acceptor specificity of Lymnaea stagnalis albumen gland UDP-GalNAc:GlcNAc beta-R beta 1-->4-N-acetylgalactosaminyltransferase: synthesis of GalNAc beta 1-->4Glc.

“…In the presence of this protein the Km for Me-3,6-Me2HexN(Me)Ac (Table 3), indicating that a disaccharide had been formed consisting of a terminal Nacetylhexosamine linked to the C-4 of another N-acetylhexosamine residue. Earlier this product had been identified as GalNAc,31-> 4GlcNAc by 1H-NMR spectroscopy (37). Incubation of ,34-GalNAcT, UDP-GalNAc, and Glc in the presence of a-LA resulted in a disaccharide that upon methylation analysis yielded two major products in almost equimolar amounts, Me-3,4,6-Me3HexN(Me)Ac and Me-2,3,6-Me3Hex (Table 3), in addition to two minor products, Me-2,3-Me2Hex and Me-2,6-Me2Hex, which probably resulted from some undermethylation or demethylation.…”

Conversion of GalNAcβ(1–4)GlcNAcβ‐OMe into GalNAcβ(1–4)‐[Fucα(1–3)]GlcNAcβ‐OMe using human milk α3/4‐fucosyltransferase synthesis of a novel terminal element in glycoprotein glycans

“…This finding implies that for a Galfl(l~)GlcNAcfll-R specific fucosyltransferase the OH group at C-2' can be replaced by a NAc group without a gross effect on the enzyme activity. Interestingly, it has been found previously that the Galfl(1M)GlcNAcfll-R ~(2-6)-sialyltransferase whether isolated from rat liver [10,21] or bovine colostrum [22] also can act on GalNAcfl(1-4)GlcNAcfll-R with high efficiency. In view of these results it will be of interest to investigate whether other Galfl(1M)GlcNAcfll-R specific glycosyltransferases such as a(2 3)-sialyltransferase [23], a3-galactosyltransferase [24] and fl3-N-acetylglucosaminyltransferase [25] are similarly capable of acting on GalNAcfl(1-4)GlcNAcfll-R.…”

Functional Characterization of Drosophila Sialyltransferase

“…Bovine and rat ST6Gal I sialyltransferases have been shown to utilize LacdiNAc as an acceptor in vitro (49,73,74), and the existence of sialylated LacdiNAc on mammalian glycoproteins suggests that these sialyltransferases, in addition to LacNAc, may also sialylate LacdiNAc termini in vivo. However, all previously characterized ST6Gal I sialyltransferases preferred LacNAc-terminating acceptors to other structures (57), including LacdiNAc (49,73,74). The recently characterized hST6Gal II also exhibited a preference for LacNAc, but its activity toward LacdiNAc structures was not examined (7,8).…”