A bait and switch hapten strategy generates catalytic antibodies for phosphodiester hydrolysis

Abstract

General base catalysis supplied by the histidine-12 (H-12) residue of ribonuclease (RNase) A has long been appreciated as a major component of the catalytic power of the enzyme. In an attempt to harness the catalytic power of a general base into antibody catalysis of phosphodiester bond hydrolysis, the quaternary ammonium phosphate 1 was used as a bait and switch hapten. Based on precedence, it was rationalized that this positively charged hapten could induce a counter-charged residue in the antibody binding site at a locus suitable for it to deprotonate the 2′-hydroxyl group of the anhydroribitol phosphodiester substrate 2. After murine immunization with hapten 1, mAb production yielded a library of 35 antibodies that bound to a BSA-1 conjugate. From this panel, two were found to catalyze the cyclization-cleavage of phosphodiester 2. Kinetic studies at pH 7.49 (Hepes, 20 mM) and 25°C showed that the most active antibody, MATT.F-1, obeyed classical Michaelis–Menten kinetics with a K _m = 104 μM, a k _cat = 0.44 min^{− 1}, and a k _cat/k _uncat = 1.7 × 10³. Hapten 1 stoichiometrically inhibits the catalytic activity of the antibody. MATT.F-1 is the most proficient antibody–catalyst (1.6 × 10⁷ M^{− 1}) yet generated for the function of phosphodiester hydrolysis and emphasizes the utility of the bait and switch hapten paradigm when generating antibody catalysts for processes for which general-base catalysis can be exploited.