CONFORMATIONAL ISOMERISM AND THE DIVERSITY OF ANTIBODIES

The fact that one cell encodes a single antibody sequence does not nec essarily mean that the resulting antibody folds into a single structur e, although this is a common assumption. Here we challenge this view a nd suggest that many antibodies do not have a single conformation at t he combining site. The basis for this proposal comes from the kinetic analysis of a set of murine hybridomas derived from defined stages of the immune response to 2-phenyl-5-oxazolone (Ox). Among them we have i dentified three antibodies that exhibit complex hapten-binding kinetic s. We observed biphasic or triphasic reactions in stopped-flow fluores cence experiments, indicating that ligand binding involved isomerizati on, as well as associative steps. The existence of an equilibrium betw een at least two antibody conformations, with ligands binding preferen tially to one form, was deduced from the variation with hapten concent ration of the apparent rate of each phase.