'Wave-type' structure of a synthetic hexaglycosylated decapeptide: A part of the extracellular domain of human glycophorin A

The three-dimensional structure of a glycopeptide, His-Thr*-Ser*-Thr*-Ser*- Ser*-Ser*-Val-Thr-Lys, with 2-acetamido-2-deoxy-alpha-D-galactose (GalNAc) residues linked to six adjacent amino acids from Thr-10 to Ser-15, was stud ied by NMR spectroscopy and molecular dynamics (MD) simulations. The hexagl ycosylated decapeptide is part of the extracellular domain of human glycoph orin A and shows an extended structure of the peptide backbone due to O-gly cosylation. Furthermore, each GalNAc residue exhibits one and only one NOE contact from the NHAc proton to the backbone amide proton of the amino acid that the sugar is directly bound to. This indicates a strong preference fo r the orientation of all GalNAc residues towards the N-terminus. NOE build- up curves were used to determine 42 inter-proton distances that, in connect ion with phi angles of the peptide backbone obtained from (3)J-coupling con stants, resulted in constraints for a MD simulation in water. The NMR data and the MD simulations show a preference for an extended backbone structure . The GalNAc residues are located alternatingly on opposite sides of the ba ckbone and reduce the flexibility of the peptide backbone. The conformation of the molecule is relatively rigid and shows a 'wave-type' 3D structure o f the peptide backbone within the glycosylation cluster. This new structura l element is also supported by the unusual CD spectrum of the glycopeptide.