Conformation of glycopeptides.

The presence of carbohydrate side-chains in native glycoproteins alters a number of biochemical properties of the peptide backbone. One of the most frequently studied questions is the conformation-modifying effect of sugar incorporation into asparagine, serine and threonine residues. When N-glycosylation modifies the conformation, the resulting structures are more ordered than the peptide chain without sugar addition. For O-glycopeptides the final conformations can be either more ordered or less ordered. In any event, only the innermost carbohydrates make contact with the peptide backbone. Through-space structural changes are mostly found downstream of the O-glycosylation site. In the repeat unit of epithelial mucin-1 protein, clustering of the carbohydrates results in an easily observable stabilization of the poly-proline II helix.