Screening of deoxyribonuclease I inhibitors from autodisplayed Fv-antibody library

Deoxyribonuclease (DNase) I inhibitors have been developed based on proteins, nucleotides and synthetic compounds. In this work, amino acid sequences with the activity of DNase I inhibitor were screened from an Fv-antibody library expressed on the outer membrane of Escherichia coli. The Fv-antibody indicated the heavy chain variable region (V_H) of immunoglobulin G (IgG) and the Fv-antibody library was generated with a randomized complementarity-determining region 3 (CDR3). From the Fv-antibody library, two clones were screened for their binding affinity to DNase I and expressed as soluble recombinant proteins as well as peptides. The binding affinity (K_D) to DNase I was estimated for the expressed Fv-antibodies (73.4 nM for Fv-1 and 89.0 nM for Fv-19) and synthesized peptides (279.2 nM for Peptide-1 and 243.2 nM for Peptide-19) using SPR biosensor. The inhibitory activity (IC₅₀) of the expressed Fv-antibodies (550.0 nM for Fv-1 and 660.2 nM for Fv-19) and synthetic peptides (864.5 nM for Peptide-1 and 974.6 nM for Peptide-19) was measured using agarose-gel assay and TaqMan-like fluorescence assay. These IC₅₀ values indicated that both expressed Fv-antibodies and synthesized peptides exerted an effective inhibitory activity against DNase I. The interaction between the screened inhibitors and DNase I was analyzed by docking simulation.