Localisation of a protein core-specific epitope from gastrointestinal mucin (MUC2). The effect of epitope immobilisation on antibody recognition.

Human intestinal mucins are high molecular weight glycoproteins which protect and lubricate the epithelium of the gastrointestinal tract. In cases of malignant disease, mucins are abnormally expressed, overproduced or underglycosylated. This feature may enable the mucins to serve as tumour markers. The MUC2 mucin largely consists of a variable number of tandem repeats of a 23 amino acid sequence, 1PTTTPITTTTTVTPTPTPTGTQT23. In this study we have localised the minimal and the optimal epitope within this region by the previously developed protein core specific 996 monoclonal antibody using synthetic peptides. Several overlapping and truncated peptides related to the tandem repeat unit have been prepared by solid-phase methodology. Other mucin peptides were synthesised on the tips of polyethylene pins, and these remained C-terminally attached to the pins for comparative investigations. The interaction of the 996 monoclonal antibody with the synthetic peptides was studied either in solution by competition RIA or on immobilised peptides by indirect ELISA experiments. These experiments show that the minimal epitope recognised by the 996 antibody is the Ac-19TGTQ22 (IC50=3100 microM in solution). For the optimal 996 antibody binding in solution the 16PTPTGTQ22 heptapeptide (IC50 = 3 microM) is required.