Understanding the Impact of Methionine Oxidation on the Biological Functions of IgG1 Antibodies Using Hydrogen/Deuterium Exchange Mass Spectrometry.

Hydrogen/deuterium exchange mass spectrometry (HDX MS) was used in two case studies to evaluate the impact of methionine (Met) oxidation on the biological functions of IgG1 antibodies. In the first case study, linear correlations were observed between the oxidation of the conserved Fc methionine residues and the loss of neonatal Fc receptor (FcRn) binding and complement-dependent cytotoxicity (CDC) activity. Both heavy chain (HC) residues Met257 and Met433 were located near the FcRn binding interface as indicated by HDX MS and structural modeling; however, HC Met257 oxidation was further demonstrated to have a more significant impact on FcRn binding than HC Met433 oxidation. In addition, oxidation of HC Met257 and HC Met433 could disrupt protein conformation at the C2-C3 interface and prevent IgG oligomerization, which is needed for C1q binding and subsequent CDC activity. In the second case study, HDX MS demonstrated that oxidation of the two complementary determining region (CDR) methionine residues had little or no impact on antigen binding of the antibody. Together, these results suggested that HDX MS is a powerful tool for evaluating the impact of individual post translational modifications (PTMs) on the biological activities of antibodies, even when the PTM levels are relatively low. The high selectivity and sensitivity of this method makes it a valuable tool for assisting the critical quality attributes (CQAs) assessment of antibodies.