Metal-dependent amyloid β-degrading catalytic antibody construct

Catalytic antibodies (catabodies) that degrade target antigens rapidly are rare. We describe the metal-dependence of catabody construct 2E6, an engineered heterodimer of immunoglobulin light chain variable domains that hydrolyzes amyloid beta peptides (A beta) specifically. In addition to the electrophilic phosphonate inhibitor of serine proteases, the metal chelators ethylenediaminetetraacetic acid (EDTA) and 1,10-phenanthroline completely inhibited the hydrolysis of A beta by catabody 2E6. Formation of catabody-electrophilic phosphonate inhibitor adducts was unaffected by EDTA, suggesting that the metal exerts a favorable effect on a catalytic step after the initial catabody nucleophilic attack on Aft The EDTA inactivated catabody failed to disaggregate fibrillar A beta, indicating the functional importance of the A beta hydrolytic activity. Treating the EDTA-inactivated catabody with Zn2+ or Co2+ restored the A beta hydrolytic activity, and Zn2+-induced catabody conformational transitions were evident by fluorescence emission spectroscopy. The studies reveal the absolute catabody dependence on a metal cofactor. (C) 2014 Elsevier B.V. All rights reserved.