POTENT ENZYME-INHIBITORS DERIVED FROM DROMEDARY HEAVY-CHAIN ANTIBODIES

Evidence is provided that dromedary heavy-chain antibodies, in vivo-ma tured in the absence of light chains, are a unique source of inhibitor y antibodies. After immunization of a dromedary with bovine erythrocyt e carbonic anhydrase and porcine pancreatic alpha-amylase, it was demo nstrated that a considerable amount of heavy-chain antibodies, acting as true competitive inhibitors, circulate in the bloodstream. In contr ast, the conventional antibodies apparently do not interact with the e nzyme's active site. Next we illustrated that peripheral blood lymphoc ytes are suitable for one-step cloning of the variable domain fragment s in a phage-display vector, By bio-panning, several antigen-specific single-domain fragments are readily isolated for both enzymes. In addi tion we show that among those isolated fragments active site binders a re well represented. When produced as recombinant protein in Escherich ia coli, these active site binders appear to be potent enzyme inhibito rs when tested in chromogenic assays. The low complexity of the antige n-binding site of these single-domain antibodies composed of only thre e loops could be valuable for designing smaller synthetic inhibitors.