Acetylcholine binding protein

Function

Acetylcholine binding protein (AChBP) is secreted by snails into cholinergic synapses, where it modulates transmission by binding acetylcholine (ACh). Sequence alignment revealed high similarity to the extracellular domains of the ligand-binding subunits of the nicotinic acetylcholine receptor (nAChR).

Structural highlights

The crystal structure of the AChBP homopentamer indeed provides a valuable model for identifying the nature of the ligand-binding domains and of the subunit interfaces of the nAChR. Furthermore, crystal structures of complexes of AChBP with various agonists and antagonists have provided detailed insight into the neurotransmitter binding site of nAChRs. The binding site of AChBP is located at the interface of neighboring subunits.

Relevance

Like the nAChR, AChBP - with ca. 20% sequence similarity - binds agonists and antagonists like ACh, nicotine, α-bungarotoxin, epibatidine with similar affinities hence it is a useful tool for understanding nAChR activity. Both receptors contain a Cys-Cys loop at the subunits interface as well as conserved residues at the ACh binding site.