β‐Galactosidase: Immune recognition of conformation and mechanism of antibody‐induced catalytic activation

Activation of mutant β‐galactosidase by antibodies can be explained by a “selection” mechanism in which the antibody binds and stabilizes those mutants in a native‐like conformation and by an “induction” mechanism where binding of the antibody itself induces a conformational change activating β‐galactosidase. The “selection” hypothesis was tested by passing β‐galactosidase through a column packed with monoclonal antibody‐derivatized Sepharose. The antibody retains the active, in preference to the inactive, proteins. The “induction” mechanism was tested by mixing antibody–Sepharose with mutant β‐galactosidase and measuring enzyme activity before mixing and that remaining in the supernatant. The activity of the antibody–Sepharose pellet exceeded the sum of the original activity plus supernatant activity. As a result of these experiments, both mechanisms are found to be operative.