Antibody-mediated activation of genetically defective Escherichia coli beta-galactosidases by monoclonal antibodies produced by somatic cell hybrids.

Abstract

Six hybridomas [from mouse spleen cell/myeloma cell hybrids] producing monoclonal antibodies against E. coli .beta.-galactosidase (.beta.-D-galactoside galoctohydrolase, EC 3.2.1.23) were derived from 2 separate somatic cell fusions. Three of these antibodies can activate defective enzymes produced by strains of E. coli carrying Z-gene point mutations. In antigen excess, 1 monoclonal antibody shows similar enzyme binding and mutant-activating capacity. Characteristically, the former reaction has a 200-fold higher equilibrium constant. The enzyme-activation reaction is a single-hit event in which 1 antibody site favors the correct conformation of 1 active center of the enzyme. Because each activating hybridoma is able to activate several, but not all point mutant enzymes tested, it appears that the correction of the genetic defect is produced by binding key sites of the protein 3-dimensional structure rather than the sites affected by the mutation.