Three residues in CDR-H3 are important for antigen-antibody binding.

<p>The binding activities of alanine scanning mutants of CDR-H3 (<b>A</b>) and CDR-L3 (<b>B</b>) were analyzed by ELISA. <b>C</b>, Quantitative dissociation kinetics of indicated mutants were analyzed by surface plasmon resonance. HER2-ECD protein was immobilized on a CM5 sensor chip followed by exposure to indicated mutant Fab antibodies. The 100% association was defined as the response unit (RU) at 200 seconds from the beginning of Fab injection. <i>k</i>_off values were calculated using the BIAevaluation software.