Solution structure of the all l- and d-amino acid-substituted mucin 2 epitope peptides

High-molecular-weight mucin 2 (MUC2) glycoproteins show an aberrant glycosylation pattern when expressed in human colon carcinoma: the oligosaccharide chains are shorter and some are missing. In our ongoing effort of MUC2 vaccine development, we have solved the NMR structure of the all l-amino acid and various d-amino acid-substituted derivatives of the peptide TPTPTGTQTPT, previously identified as an epitope within the tandem repeat unit of the MUC2 glycoprotein. In the all l-amino acid containing peptide and in peptide tpTPTGTQtpt (where lowercase letters mark the position of d-amino acids) we identified a type I β-turn spanning through residues 3TPTG 6 and 5TGTQ 8, respectively. Our structural findings are in good agreement with the antibody recognition properties of the investigated peptides and demonstrate that peptides with good stability against enzymatic degradation can be designed with good antibody binding characteristics.