title: Mechanical stability of the antibody domain CH3 homodimer in different oxidation states.
abstract: The CH3 homodimer at the C-terminal end of the antibody heavy chain is the key noncovalent interaction stabilizing antibody proteins. Here, we use single-molecule force spectroscopy to investigate the dissociation mechanics of CH3 as a proxy for antibody mechanical stability. We find the CH3 homodimer to be a highly stable complex, and its dissociation force of >150 pN at a loading rate of ≈5500 pN/s exceeds the stability of most protein-protein interactions studied to date. Separated CH3 monomers, on the other hand, are mechanically labile and only short-lived. Each CH3 monomer contains a conserved buried disulfide bridge, and we find that the successive reduction of one or both disulfide bridges in the dimer results in a stepwise decrease of the dissociation force. This suggests a structural role of the disulfide bridges helping to mold the high-affinity domain-domain interface, even though they are neither required for nor directly involved in dimerization. Taken together, our results set a limit on how much force a single antibody can bear and reveal the CH3 homodimer as a mechanical fastener that prevents antibody dissociation.
authors.affiliation: Physik Department E22, Technische Universität München , James-Franck-Straße 1, 85748 Garching, Germany.
authors.forename: Morten
authors.initials: M
authors.lastname: Bertz
authors.forename: Johannes
authors.initials: J
authors.lastname: Buchner
authors.forename: Matthias
authors.initials: M
authors.lastname: Rief
mesh_terms: D001696:Biomechanical Phenomena; D004220:Disulfides / Q000737:chemistry; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry*; D055595:Mechanical Phenomena; D008958:Models, Molecular; D018384:Oxidative Stress; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary
chemical_list: D004220:Disulfides; D007143:Immunoglobulin Heavy Chains