Antibody domain mutants demonstrate autonomy of the antigen binding site.

We have constructed derivatives of a lambda I light chain-bearing anti-(4-hydroxy,3-nitrophenyl)acetyl (NP) antibody which have the V regions exchanged between heavy chains and light chains of the kappa or lambda I type. These antibodies are assembled and secreted normally, and bind haptenic and macromolecular ligands like the wild-type; similar results are obtained for monovalent heterodimers of VHCL and lambda I light chains. The observed independence of the binding site from the constant region context argues against a role of longitudinal interactions between constant and variable domains in antigen recognition, and therefore against cooperativity between binding sites.