Contributions of a disulfide bond to the structure, stability, and dimerization of human IgG1 antibody CH3 domain

Recombinant human monoclonal antibodies have become important protein-based therapeutics for the treatment of various diseases. The antibody structure is complex, consisting of β-sheet rich domains stabilized by multiple disulfide bridges. The dimerization of the CH3 domain in the constant region of the heavy chain plays a pivotal role in the assembly of an antibody. This domain contains a single buried, highly conserved disulfide bond. This disulfide bond was not required for dimerization, since a recombinant human CH3 domain, even in the reduced state, existed as a dimer. Spectroscopic analyses showed that the secondary and tertiary structures of reduced and oxidized CH3 dimer were similar, but differences were observed. The reduced CH3 dimer was less stable than the oxidized form to denaturation by guanidinium chloride (GdmCl), pH, or heat. Equilibrium sedimentation revealed that the reduced dimer dissociated at lower GdmCl concentration than the oxidized form. This implies that the disulfide bond shifts the monomer–dimer equilibrium. Interestingly, the dimer–monomer dissociation transition occurred at lower GdmCl concentration than the unfolding transition. Thus, disulfide bond formation in the human CH3 domain is important for stability and dimerization. Here we show the importance of the role played by the disulfide bond and how it affects the stability and monomer–dimer equilibrium of the human CH3 domain. Hence, these results may have implications for the stability of the intact antibody.