Epitopes of Escherichia coli ribosomal protein S13

To analyze the immunochemical structure of Escherichia coli ribosomal protein S13 and its organization in situ, we have generated and characterized 22 S13-specific monoclonal antibodies. We used a competitive enzyme-linked immunosorbent assay to divide them into groups based on their ability to inhibit binding of one another. The discovery of five groups with distinct binding properties suggested that a minimum of five distinct determinants on S13 are recognized by our monoclonal antibodies. The locations of the epitopes detected by these monoclonal antibodies have been mapped on S13 peptides. Three monoclonal antibodies bind a S13 C-terminal 34-residue segment. All the other 19 monoclonal antibodies bind a S13 N-terminal segment of about 80 residues. The binding sites of these 19 monoclonal antibodies have been further mapped to subfragments of peptides. Two monoclonal antibodies recognized S131-22; three monoclonal antibodies bound to S131-40; the binding sites of three other antibodies have been located in S1323-80, with epitopes possibly associated with residues 40-80. The remaining 11 monoclonal antibodies did not bind to these subfragments. These data provide molecular basis to the structure of S13 epitopes, whose in situ accessibility may reveal the S13 organization on the ribosome.