Synthesis of Mucin Peptide Epitopes

Abstract

The MUC-1 mucin is a heavily glycosylated transmembrane protein found on the apical surface of the epithelial cells that contains a short cytoplasmic end and a long extracellular domain consisting of multiple 20-amino acid tandem repeat domains. In tumor cells, muc1 mucin has an alteration of the glyco chains, which makes it no longer restricted to the apical surface of the membrane and covers the entire cell surface. This study focusses on synthesizing mucin peptide epitopes that can possibly interact with the mucin monoclonal antibody. Three mucin epitopes were synthesized based on the tandem repeat domain sequence GVTSAPD, with the proline residue substituted with gamma-aminobutyric acid (GABA), D-α- phenylglycine (D-PHG) and L-α-phenylglycine (PHG). The LCMS displayed one single peak for GABA (634.3073u) and two separate peaks for D-PHG (682.3399u and 682.3331u), and PHG (682.3092u and 682.3134u). The two separate peaks of PHG and D-PHG are due to the two different steric conformers of L- and D-PHG. 2D proton NMR was used to confirm the peptide sequence. Antibody-epitope binding studies showed that the PHG derivatives can bind the antibody at the aromatic residues.