Development and Characterization of Peptide Ligands of Immunoglobulin G Fc Region

Affinity chromatography based on bacterial immunoglobulin (Ig)-binding proteins represents the cornerstone of therapeutic antibody downstream processing. However, there is a pressing need for more robust affinity ligands that would withstand the harsh column sanitization conditions, while still displaying high selectivity for antibodies. Here, we report the development of linear peptide IgG ligands, identified from combinatorial phage-display library screens. The lead peptide was shown to compete with staphylococcal protein A for the IgG Fc region. Trimming analysis and alanine scanning revealed the minimal structural requirements of the peptide for Fc binding, and the minimized peptide GSYWYQVWF recognized all human IgG subtypes. Mutation of glutamine located at the nonessential position 6 to aspartate led to the optimized peptide GSYWYDVWF with 18-fold higher affinity ( K_D app. 0.6 μM) compared to the parent peptide. When coupled to paramagnetic beads or a chromatographic matrix, the optimized ligand was shown to selectively enrich antibodies from complex protein mixtures.