Mapping the locations of the epitopes of five monoclonal antibodies to the core protein of dermatan sulfate proteoglycan II (decorin)

Antibodies to dermatan sulfate proteoglycan II (decorin) have been used to study various aspects of the structure, function, and occurrence of this proteoglycan. The epitopes of five monoclonal antibodies (7B1, 5D1, 3B3, 6D6, and 1XA) were localized to specific cyanogen bromide fragments of the protein core separated by gel filtration. One large (159 residue) cyanogen bromide peptide was further digested with endoproteinase Lys-C and the peptides separated by reversed phase high performance liquid chromatography. In this way sequences of a suitable length (21-52 residues) for epitope mapping by synthesis of overlapping hexa- and octapeptides were identified. For each of the five monoclonal antibodies a short linear sequence with antigenic activity, from 4 to 8 amino acids long, depending on the particular antibody, was identified. The locations of the epitopes were correlated with various properties of the protein core predicted from the known amino acid sequence. It was observed that, at most, only one was localized in a region predicted to involve a beta-turn. Although four epitopes were in regions predicted to be moderately hydrophilic, accessible, and flexible, one was located in a hydrophobic sequence predicted to be highly inflexible and inaccessible. The implications of this observation in relation to the function of this proteoglycan are discussed.