Structural determinants of selective alpha-conotoxin binding to a nicotinic acetylcholine receptor homolog AChBP

The nicotinic acetylcholine receptor (nAChR) is the prototype member of the super-family of pentameric ligand-gated ion channels. How the extracellular ligand-binding domain coordinates selective binding of ligand molecules to different subtypes of the receptor is unknown at the structural level. Here, we present the 2.2-Å crystal structure of a homolog of the ligand-binding domain of the nAChR, Aplysia californica AChBP (Ac-AChBP), in complex with α-conotoxin ImI. This conotoxin is unique in its selectivity toward the neuronal