Differential recognition of glycoprotein acceptors by terminal glycosyltransferases

Open Access
Publisher Website
Google Scholar
Abstract
The factors regulating modifications of terminal β-Gal residues in lactosaminyl (Gaiβ→4GlcNAcβ→R) units in intact glycoproteins are not well understood. To examine these factors, rat liver α2,3 sialyltransferase (α2,3ST) and α2,6 sialyltransferase (α2,6ST) and the murine α1,3 galac-tosyltransferase (α1,3GT) were incubated with a variety of well-defined desialylated glycoproteins and with glycoproteins in extracts of the Lec2 mutant CHO cells. Lec2 cells constitutively synthesize nonsialylated glycoproteins with terminal lactosaminyl sequences. The results demonstrate that each enzyme displays preferences for glycoprotein acceptors and in the types of N-glycans recognized. The a2,3ST, in contrast to the α2,6ST and α,3GT, prefers more branched N-glycans compared to diantennary N-glycans. However, only the α1,3GT is able to efficiently modify polylactosamines (3Galβ1→4GlcNAcβ1→)n in N-glycans. Glycopeptides were also prepared by proteolysis of Lec2 glycoproteins and tested as acceptors compared to intact Lec2 glycoproteins. The α2,6ST and α,3GT utilized intact glycoproteins and glycopeptides with a 2-fold preference for the former over the latter. In contrast, the α2,3ST showed a 20-fold preference for intact glycoproteins over glycopeptides. These results demonstrate that each of these terminal glycosyltransferases differentially recognizes glycans and glycoprotein acceptors, and that the α2,3ST requires peptide features for efficient utilization of branched N-glycan acceptors.

This publication has 0 references indexed in Scilit: