Identification of antigenic epitope for neutralizing antibody that inhibits enzymatic activity of Helicobacter pylori urease

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There may be two types of Helicobacter pylori (H.pylori) urease-specific antibodies, one is unfavorable to the body in progressing gastritis and the other is benefical in preventing bacterial growth and attachment to the gastric mucosa. To find the epitope for the latter type, a series of overlapping peptides were synthesized to identify the epitope of a mouse monoclonal antibody (mAb), termed L2, which has the capacity to generate complete suppression of the enzymatic activity of H. pylori urease. Among 79 overlapping peptides tested, a predominant epitope, UB-33 (aa 321-339; CHHLDKSIKEDVQFADSRI), was identified. Immunization with KLH-conjugated UB-33 induced UB-33-specific antibody which partially abrogated the urease activity. The minimal epitope of L2 was F8 (SIKEDVQF), whereas 6-mer peptide (KEDVQF) was the minimum for UB-33-specific rabbit sera. F8-based multiple antigenic peptides (MAP) generated UB-33-specific antibody that was much stronger than UB-33 but less potent than L2 and its minimal epitope was 6-mer (SIKEDV). The amino acid 329K seems to be critical to the L2-specific antibody response. The findings shown here provide important information on making a neutralizing vaccine to prevent H.pylori infection as well as its persistency in the stomach.