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The Binding Site of Acetylcholine Receptor
Author(s) -
FUCHS SARA,
KASHER RONI,
BALASS MOSHE,
SCHERF TALI,
HAREL MICHAL,
FRIDKIN MATI,
SUSSMAN JOEL L.,
KATCHALSKIKATZIR EPHRAIM
Publication year - 2003
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1196/annals.1254.011
Subject(s) - acetylcholine receptor , peptide , chemistry , binding site , mimotope , stereochemistry , nicotinic acetylcholine receptor , peptide library , ligand (biochemistry) , nuclear magnetic resonance spectroscopy , protein structure , receptor , torpedo , phage display , peptide sequence , biochemistry , gene
A bstract : Our group has been employing short synthetic peptides, encompassing sequences from the acetylcholine receptor (AChR) α‐subunit for the analysis of the binding site of the AChR. A 13‐mer peptide mimotope, with similar structural motifs to the AChR binding region, was selected by α‐bungarotoxin (α‐BTX) from a phage‐display peptide library. The solution structure of a complex between this library‐lead peptide and α‐BTX was solved by NMR spectroscopy. On the basis of this NMR study and on structure‐function analysis of the AChR binding site, and in order to obtain peptides with higher affinity to α‐BTX, additional peptides resulting from systematic residue replacement in the lead peptide were designed and characterized. Of these, four peptides, designated high‐affinity peptides (HAPs), homologous to the binding region of the AChR, inhibited the binding of α‐BTX to the AChR with an IC 50 of 2 nM. The solution and crystal structures of complexes of α‐BTX with HAP were solved, demonstrating that the HAP fits snugly to α‐BTX and adopts a β‐hairpin conformation. The X‐ray structures of the bound HAP and the homologous loop of the acetylcholine binding protein (AChBP) are remarkably similar. Their superposition results in a model indicating that α‐BTX wraps around the receptor binding‐site loop and, in addition, binds tightly at the interface of two of the receptor subunits, where it inserts a finger into the ligand‐binding site. Our proposed model explains the strong antagonistic activity of α‐BTX and accommodates much of the biochemical data on the mode of interaction of α‐BTX with the AChR.