Mimicking the nicotinic receptor binding site by a single chain Fv selected by competitive panning from a synthetic phage library

We have developed a novel competitive method to select from a phage display library a single chain Fv which is able to mimic the alpha -bungarotoxin b inding site of the muscle nicotinic receptor. The single chain Fv was selec ted from a large synthetic library using alpha -bungarotoxin-coated magneti c beads. Toxin-bound phages were then eluted by competition with affinity p urified nicotinic receptor. Recognition of the toxin by the anti-alpha -bun garotoxin single chain Fv was very similar to that of the receptor, such as indicated by the epitope mapping of alpha -bungarotoxin through overlappin g synthetic peptides. Moreover, several positively charged residues located in the toxin second loop and in the C-terminal region were found to be cri tical, to a similar extent, for toxin recognition by the single chain Fv an d the receptor. However, although the anti-alpha -bungarotoxin single chain Fv seems to mimic the toxin binding site of the nicotinic receptor, it doe s not bind other nicotinic agonists or antagonists. Our results suggest tha t competitive selection of anti-ligand antibody phages can allow the produc tion of receptor-mimicking molecules directly and exclusively targeted at o ne specific ligand. Since physiologically and pharmacologically different l igands can produce opposite effects on receptor functions, such selective l igand decoys can have important therapeutic applications.