Tertiary structure in N-linked oligosaccharides. Biochemistry 26,6553

ABSTRACT: Distance constraints derived from two-dimensional nuclear Overhauser effect measurements have been used to define the orientation of the Mana1-3ManP linkage in seven different N-linked oligo-saccharides, all containing the common pentasaccharide core Mana 1-6(Man(ul-3)Man~l-4GlcNAc~l-4GlcNAc. Conformational invariance of the Manal-3Manp linkage was found for those structures bearing substitutions on the Mancu1-3ManP antenna. However, the presence of either a GlcNAc residue in the @l-4 linkage to ManP ("bisecting GlcNAc") or a xylose residue in the pl-2 linkage to Man @ of the trimannosyl core was found to generate conformational transitions that were similar. These transitions were accompanied by characteristic chemical shift perturbations of proton resonances in the vicinity of the M a n a l 3 M a n p linkage. Molecular orbital energy calculations suggest that the conformational transition between the unsubstituted and substituted cores arises from energetic constraints in the vicinity of the Manal-3Manp linkage, rather than specific long-range interactions. These data taken together with ou