Specificity in the enzymic transfer of sialic acid to the oligosaccharide branches of BI- and triantennary glycopeptides of α 1-acid glycoprotein

Abstract

Partial in vitro sialylation of biantennary and triantennary glycopeptides of α 1-acid glycoprotein using colostrum β-galactosideα(2→6) sialyltransferase followed by high resolution 1H-NMR spectroscopic analysis of the isolated products enabled the assignment of the Galβ(1→4)GlcNAcβ(1→2)Man α(1→3)Man branch as the most preferred substrate site for sialic acid attachment. The Galβ(1→4)GlcNAcβ(1→2)Man α(1→6)Man branch appeared to be much less preferred and the Galβ(1→4)GlcNAcβ(1→4)Manα(1→3)Man sequence of triantennary structures was of intermediate preference for the sialyltransferase. The specificity of the β-galactoside α(2→6) sialyltransferase is thus shown to extend to structural features beyond the terminal N -acetyllactosamine units on the oligosaccharide chains of serum glycoproteins.