Specific degradation of H. pylori urease by a catalytic antibody light chain

Abstract

Catalytic antibodies capable of digesting crucial proteins of pathogenic bacteria have long been sought for potential therapeutic use. Helicobacter pylori urease plays a crucial role for the survival of this bacterium in the highly acidic conditions of human stomach. The HpU-9 monoclonal antibody (mAb) raised against H. pylori urease recognized the α-subunit of the urease, but only slightly recognized the β-subunit. However, when isolated both the light and the heavy chains of this antibody were mostly bound to the β-subunit. The cleavage reaction catalyzed by HpU-9 light chain (HpU-9-L) followed the Michaelis-Menten equation with a Km of 1.6 × 10-5 M and a kcat of 0.11 min-1, suggesting that the cleavage reaction was enzymatic. In a cleavage test using H. pylori urease, HpU-9-L efficiently cleaved the β-subunit but not the á-subunit, indicating that the degradation by HpU-9-L had a specificity. The cleaved peptide bonds in the β-subunit were L121-A122, E124-G125, S229-A230, Y241-D242, and M262-A263. BSA was hardly cleaved by HpU-9-L, again indicating the digestion by HpU-9-L was specific. In summary, we succeeded in the preparation of a catalytic antibody light chain capable of specifically digesting the β-subunit of H. pylori urease. © 2005 FEBS.