Noncovalent antibody catenation on a target surface drastically increases the antigen-binding avidity

Immunoglobulin G (IgG) antibodies are widely used for diagnosis and therapy. Given the unique dimeric structure of IgG, we hypothesized that, by genetically fusing a homodimeric protein (catenator) to the C-terminus of IgG, reversible catenation of antibody molecules could be induced on a surface where target antigen molecules are abundant, and that it could be an effective way to greatly enhance the antigen-binding avidity. A thermodynamic simulation shows that quite low homodimerization affinity of a catenator, e.g. dissociation constant of 100 μM, can enhance nanomolar antigen-binding avidity to a picomolar level, and that the fold enhancement sharply depends on the density of the antigen. In a proof-of-concept experiment where antigen molecules are immobilized on a biosensor tip, C-terminal fusion of a weakly homodimerizing protein to two different antibodies enhanced the antigen-binding avidity by at least 210 to 5,120 folds from the intrinsic binding avidity. Thus, the homodimerization-induced antibody catenation would be a simple, powerful and general approach to improve many antibody applications, including the detection of scarce biomarkers and targeted anticancer therapies.