The interaction of the acetylcholine receptor (AChR) binding site domain with specific antibodies and with α-bungarotoxin (α-BTX) has been compared. The cloned and expressed ligand binding domain of the mouse AChR α-subunit binds α-BTX, whereas the mongoose-expressed domain is not recognized by α-BTX. On the other hand, both the mouse and mongoose domains bind to the site-specific monoclonal antibody 5.5. These results demonstrate that the structural requirements for binding of α-BTX and mcAb 5.5, both of which interact with the AChR binding site, are distinct from each other.
