¹H NMR studies on the solution conformation of contulakin-G and analogues

The conformation of contulakin-G, a bioactive 16 amino acid O-linked glycopeptide (ZSEEGGSNAT*KKPYIL) with the disaccharide β-D-Gal(1[Formula: see text]3)α-D-GalNAc attached to the threonine residue in position 10, has been investigated by 1H NMR spectroscopy. The 1H NMR data for the non-glycosylated peptide and for two glycopeptide analogues, one with the monosaccharide α-D-GalNAc at Thr10 and one with the disaccharide β-D-Gal(1–>3)α-D-GalNAc at Ser7, all of lower bioactivity than contulakin-G, have also been collected. The chemical shifts, NOEs, temperature coefficients of amide protons, and 3JNH,αH-values suggest that all four compounds exist mainly in random coil conformations. Some transient populations of folded conformations are also present in the glycopeptides and turns, probably induced by the sugars, are present in the peptide chain around the site of glycosylation. In the two peptides O-glycosylated at Thr10, the rotation of α-D-GalNAc around the linkage between the sugar and the peptide is restricted. There is evidence for a hydrogen bond between the amide proton of α-D-GalNAc and the peptide chain that could contribute to this torsional rigidity. An intramolecular hydrogen bond between the carbohydrate and the peptide chain does not exist in the peptide O-glycosylated at the Ser7 residue. Key words: conformation, contulakin-G, NMR, O-linked glycopeptide.