A catalytic antibody heavy chain HpU-2 degrading its epitope peptide and H. pylori urease

The HpU-2 monoclonal antibody (mAb) raised against Helicobacter pylori urease mainly recognized the α-subunit of the urease. On the other hand, the heavy chain of HpU-2 mAb (HpU-2-H) isolated from the parent mAb recognized both the α- and β-subunit, in which the β-subunit was recognized more strongly than the β-subunit. HpU-2-H cleaved a peptide, SVELIDIGGNRRIFGFNALVD, which is the epitope sequence recognized by HpU-2 mAb, showing a double-phase reaction profile at 25 °C in a phosphate buffer. After an induction time of 24 h, the cleavage of the peptide was initiated by HpU-2-H at a high rate and it was completed at 80 h of incubation. By mass spectroscopy, two main fragmented peptides, SVELIDIGGNRR and SVELIDIGGNRRIFG, were identified. In addition, many small peptide fragments were produced by successive cleavage of the fragmented peptides. Cleavage tests for H. pylori urease by HpU-2-H revealed that the β-subunit of the urease was cleaved first and completely decomposed at 20 h of incubation. Cleavage of the α-subunit started after the complete decomposition of the β-subunit. These cleavage results were in good agreement with the immunological features of HpU-2-H. The irrelevant proteins, BSA and HSA, were hardly cleaved by HpU-2-H.