Influence of the Extent of Branching on Solution Conformations of Complex Oligosaccharides: A Molecular Dynamics and NMR Study of a Penta-Antennary "Bisected" N-Glycan

The solution conformation of an agalactosyl penta-antennary "bisected" N-linked glycan from hen ovomucoid has been determined using a combination of 1H-NMR NOE measurements and restrained molecular dynamics (MD) simulations. The majority of glycosidic linkages exhibited restricted torsional fluctuations about the global minimum energy configuration, of an extent which was generally less than that observed in N-linked glycans with a smaller number of antennae. The locations of terminal galactose residues in the native glycan, which exhibit branch specificity, could not readily be rationalized in terms of relative accessibility by the relevant galactosyltransferase of the various nonreducing terminal 2-acetamido-2-deoxy-D-glucopyranose (GlcNAc) residues in the agalactosyl glycan, suggesting either that the parent protein exhibits substantial control over glycosylation or that more than one transferase is responsible for galactosylation.