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Development of the Double Cyclic Peptide Ligand for Antibody Purification and Protein Detection.

Development of a peptide-based affinity matrix and detection reagent is important for biomedical research and the biopharmaceutical industry. In the present work, we designed and synthesized an immunoglobin G (IgG)-binding peptide ligand, Fc-III-4C. Fc-III-4C is composed of 15 residues, and the 4 cysteine residues form 2 disulfide bonds to generate a double cyclic structure. The binding affinity of the Fc-III-4C peptide toward human IgG was determined to be 2.45 nM (Kd), which is higher than that of IgG with Protein A/G (Pro-A/G). Importantly, the Fc-III-4C peptide displayed high affinity to various IgGs from different species. Fc-III-4C immobilized agarose beads exhibited high stability and reusability when compared with that of the Pro-A/G-immobilized beads. The conjugate of Fc-III-4C with FITC was demonstrated to be suitable for immunofluorescence detection of proteins expressed in cells. These results demonstrate that the Fc-III-4C peptide is a useful affinity ligand for antibody purification and as a protein detection reagent.