Conformational analysis of O-linked glycopeptides related to enkephalin and nuclear pore proteins

The effect of O-linked glycosylation on peptide conformation has been studied in pursuit of understanding one of the natural roles of carbohydrates, and with an interest in drug design. Solution conformations were analyzed using a combination of NMR, molecular modeling, and kinetics techniques. Variations in peptide sequence, carbohydrate, and stereochemistry of linkage were made. Glycosylation of enkephalin analogs at the Ser⁶ position of the sequence Tyr-c-[D-cys-Gly-Phe-D-cys]-Ser-Gly-CONH₂ with a glucose moiety affected only the exocyclic portion of the molecule. An α-linkage constrained the carbohydrate and lessened the impact on peptide conformation, when compared to a β-linkage. Glycosylation of nuclear pore protein models of the sequence c-[Cys-Ser-Pro-Ser-Thr-Cys] at the Ser⁴ position increased turn formation irrespective of carbohydrate identity or linkage. Glycosylation of the uncyclic form of this sequence at Ser⁴ demonstrated no conformational differences. Flexibility of the unglycosylated sequence is paramount in determining the potential impact of glycosylation since two completely different effects are observed for glycosylation of the cyclic and uncyclic sequence