Analysis of the linear epitope for Fc-binding on the mouse IgG Fc receptor (moFcγRI) by synthetic peptide

To identify the linear epitope for Fc-binding to the mouse immunoglobulin G (IgG) Fc receptor (moFcγRI), peptides derived from the membrane-distal extracellular domain (EC2) of moFcγRI, corresponding to the homologous region of human FcγRI (huFcγRI) and huFcγRII, were synthesized. Using a dot-blot assay, six peptides were tested. The results showed that the moRI3 peptide (CVFYRNGKSFQFS) could combine with mouse IgG efficiently. A competitive enzyme-linked immunosorbent assay (ELISA) showed that the IC50 value of the moRI3 peptide was 38.03 mM. The moRI3 peptide could inhibit the combination of mouse IgG to the transfected COS 7 cells significantly with an IC50 value of 72.68 mM. The IgG-binding region of moFcγRI was also localized in the C'-E loop of the EC2 domain as predicted according to huFcγRI and huFcγRII. We predicted that the minimum effective IgG-binding region of moFcγRI may be the peptide 153SFQFSS158. The linear epitope for immunoglobulin-binding to mouse FcγR is also described. Thus, we generated a peptide that targets a fundamental aspect of ligand recognition by this receptor class.