pH and Conformation Modulate Copper-Mediated Site-Specific Degradation of the IgG1 Hinge Region

Abstract

Fragmentation in the hinge region of an IgG1 monoclonal antibody (mAb) can impact product stability, potentially causing changes in potency and efficacy. Metals ions, such as Cu2+, can bind to the mAb and undergo hydrolysis and/ or oxidation, which can lead to cleavage of the molecule. To better understand the mechanism of Cu2+-mediated mAb fragmentation, hinge region cleavage products and their rates of formation were studied as a function of pH with and without Cu2+. More detailed analysis of the chemical changes was investigated using model linear and cyclic peptides (with the sequence of SCDKTHTC) derived from the upper hinge region of the mAb. Cu2+ mediated fragmentation was determined to be predominantly via a hydrolytic pathway in solution. The sites and products of hydrolytic cleavage are pH and strain dependent. In more acidic environments, rates of Cu2+ induced hinge fragmentation are significantly slower than at higher pH. Although the degradation reaction rates between the linear and cyclic peptides are not significantly different, the products of degradation vary. mAb fragmentation can be reduced by modifying His, which is a potential metal binding site and a known ligand in other metalloproteins. These results suggest that a charge may contribute to stabilization of a specific molecular structure involved in hydrolysis, leading to the possible formation of a copper binding pocket that causes increased susceptibility of the hinge region to degradation.