Kinetics-Based Structural Requirements of Human Immunoglobulin G Binding Peptides

[Image: see text] Currently, antibodies are widely used not only in research but also in therapy. Hence, peptides that selectively bind to the fragment crystallizable site of an antibody have been extensively utilized in various research efforts such as the preparation of antibody–drug conjugates (ADC). Consequently, appropriate peptides that bind to immunoglobulin G (IgG) with a specific K(d) value and also k(on) and k(off) values will be useful in different applications, and these kinetic parameters have been perhaps overlooked but are key to development of peptide ligands with advantageous binding properties. We prepared structural derivatives of IgG-binding peptide 1 and evaluated the binding affinity and kinetic rates of the products by surface plasmon resonance assay and isothermal titration calorimetry to obtain novel peptides with beneficial antibody binding properties. In this way, 15-Lys8Leu with fast-binding and slow-release features was obtained through a shortened peptide 15-IgBP. On the other hand, we successfully obtained distinctive peptide, 15-Lys8Tle, with a similar K(d) value but with k(on) and k(off) values that were as much as six-fold different from those of 15-IgBP. These new peptides are useful for the elucidation of kinetic effects on the function of IgG-binding peptides and various applications of antibody or antibody–drug interactions, such as immunoliposome, ADC, or half-life extension strategy, by using a peptide with the appropriate kinetic features.