Antibody-Mediated Screening of Peptide Inhibitors for Monoamine Oxidase‑B (MAO-B) from an Autodisplayed FV Library

Inhibitors for monoamine oxidase-B (MAO-B) were screened from an FV library with a randomized complementarity-determining region 3 (CDR3) region using a monoclonal antibody against dopamine. As the first step, the FV library was expressed on the outer membrane of E. coli by site-directed mutagenesis of the randomized CDR3 region. Among the FV library, variants with a binding affinity to monoclonal antibodies against dopamine were screened and cloned. From the comparison of the binding activity of the screened clones to a control clone with a modified FV antibody (only with CDR1 and CDR2), the CDR3 regions of screened clones were determined to directly interact with the monoclonal antibody against dopamine. These CDR3 sequences were then synthesized as mimotopes (mimicking peptides) of dopamine. The inhibitory activity of two mimotopes against MAO-B was analyzed using HeLa cells overexpressing MAO-B, as well as using activated human astrocytes; their inhibitory activity was compared to that of a commercial inhibitor of MAO-B, selegiline. The inhibition efficiency of the two mimotopes (in comparison with selegiline) was estimated to be 67.2% and 69.4% in the HeLa cells and 64.4% and 58.0% in the human astrocytes. The gene expression pattern in astrocytes after treatment with the two mimotopes was also analyzed and compared with that in the human astrocytes treated with selegiline. Finally, the interaction between two mimotopes and MAO-B was analyzed using docking simulation, and the candidate regions of MAO-B for the interaction with each mimotope were explored through the docking simulation.