Bisecting GlcNAc restricts conformations of branches in model N-glycans with GlcNAc termini

Bisected N-glycans play significant roles in tumor migration and Alzheimer's disease through modulating the action and localization of their carrier proteins. Such biological functions are often discussed in terms of the conformation of the attached N-glycans with or without bisecting GlcNAc. To obtain insights into the effects of bisecting GlcNAc on glycan conformation, a systematic NMR structural analysis was performed on two pairs of synthetic N-glycans, with and without bisecting GlcNAc. The analysis reveals that terminal GlcNAcs and bisecting GlcNAc cooperate to restrict the conformations of both the alpha 1-3 and alpha 1-6 branches of N-glycans. H-1 and C-13 chemical shift comparisons suggest that bisecting GlcNAc directly modulates local conformation. Unique NOE correlations between core-mannose and the alpha 1-3 branch mannose as well as the (3)J(C)-H constant of the glycoside linkage indicate that bisecting GlcNAc restricts the conformation of the 1-3 branch. The angles of the glycosidic bonds between core-mannose and alpha 1-6 branch mannose derived from (3)J(C)-H and 3JH-H coupling constants show that terminal GlcNAcs restrict the distribution of the psi angle to 180 degrees and the bisecting GlcNAc increases the distribution of the omega angle +60 degrees in the presence of terminal GlcNAcs. It is feasible that restriction of branch conformations by bisecting GlcNAc has important consequences for protein-glycan interplay and following biological events. (C) 2017 Elsevier Ltd. All rights reserved.