Mutational and inhibitory analysis of a catalytic antibody. Implication for drug discovery.
Résumé
Data on catalytic antibodies (abzymes) having critical roles in pathologies, for example in some auto-immune diseases accumulate at overwhelming pace. Nevertheless, the misunderstanding of how antibodies can mimic a catalytic activity may hamper the development of therapeutic tools. We thus investigated the structure function roles of residues of a catalytic antibody endowed with a β-lactamase activity. The catalytic antibody 9G4H9 was generated using the internal image properties of anti-idiotypic antibodies. The single-chain fragment was cloned and produced in Escherichia coli. Based on the structure function knowledge of β-lactamases pattern and on the tridimensional model of the scFv, five residues were selected for mutagenic analysis to learn about the contribution of putative residues in catalysis. Light chain mutants R24A, S26A, S28A, and E98A lost catalytic activity significantly. Mutant K27A retained catalytic activity but the estimated KM was affected. Kinetic outcomes support the argument that S26 and S28 function as nucleophile and E98 as general acid/base catalyst.