Impact of methionine oxidation on the binding of human IgG1 to FcRn and Fcγ receptors

Methionine oxidation commonly occurs in the Fc fragment of therapeutic monoclonal antibodies; however, its impact on antibody function has not been addressed. Using surface plasmon resonance and cell binding assays, we examined the impact of methionine oxidation on the binding of two humanized IgG1 antibodies to Fcγ receptors (FcγR) and to the neonatal Fc receptor (FcRn). A panel of FcγRs, including FcγRI, FcγRIIa–131H, FcγRIIa–131R, FcγRIIb/c, FcγRIII ALF, FcγRIII ALV, and FcγRIIIb was evaluated. The binding of oxidized IgG1 molecules to individual receptors remained the same with the exception of FcγRIIa where a subtle decrease in binding to the 131H allele was observed. In contrast, but in agreement with recently reported structural changes associated with Met oxidation, binding to FcRn was significantly affected. An increase in KD values at pH 6.0 was observed with increasing degree of oxidation, reaching several-fold greater value in highly oxidized samples. To our knowledge this is the first report demonstrating that chemical degradations in the constant region of monoclonal antibodies can impact their function and it highlights the importance of avoiding oxidation in therapeutic antibodies.