Recognition of Human IgG1 by Fcγ Receptors: Structural Insights from Hydrogen-Deuterium Exchange and Fast Photochemical Oxidation of Proteins Coupled with Mass Spectrometry

Antibody-dependent cell-mediated cytotoxicity (ADCC) is an effector function of immunoglobulins (IgGs) involved in the killing of target cells by a cytotoxic effector cell. Recognition of IgG by Fc receptors expressed on natural killer cells, mostly Fc gamma III receptors (Fc gamma RIII), underpins the ADCC mechanism, thus motivating investigations of these interactions. In this paper, we describe the combination of hydrogen-deuterium exchange and fast photochemical oxidation of proteins (FPOP) coupled with mass spectrometry to study the interactions of the human IgG1/Fc gamma RIII complex. Using these orthogonal approaches, we identified critical peptide regions and residues involved in the recognition of IgG1 by Fc gamma RIII. The footprinting results are consistent with the previously published crystal structure of the IgG1 Fc/Fc gamma RIII complex. Additionally, our FPOP results reveal the conformational changes in the Fab domain upon binding of the Fc domain to Fc gamma RIII. These data demonstrate the value of footprinting as part of a comprehensive toolbox for identifying the changes in the higher-order structure of therapeutic antibodies in solution.