The relation of three-dimensional structure to biosynthesis in the N-linked oligosaccharides

The three-dimensional structures are presented for representative N-linked oligosaccharides drawn from four major structural classes. The nuclear magnetic resonance evidence leading to these structures is summarized and the conclusions are compared with those obtained from potential energy calculations and from the crystal structures of fragments. The major finding is that the Man alpha 1-3 arm structure is invariant throughout the series, whereas the Man alpha 1-6 arm has two possible orientations in some structures and a single orientation in others. Finally, the three-dimensional structures permit a rationalization of the substrate specificity of several key enzymes in the biosynthetic pathway.