TY - JOUR
T1 - Curariform antagonists bind in different orientations to acetylcholine-binding protein
AU - Gao, Fan
AU - Bren, Nina
AU - Little, Alicia
AU - Wang, Hai Long
AU - Hansen, Scott B.
AU - Talley, Todd T.
AU - Taylor, Palmer
AU - Sine, Steven M.
PY - 2003/6/20
Y1 - 2003/6/20
N2 - Acetylcholine-binding protein (AChBP) recently emerged as a prototype for relating structure to function of the ligand binding domain of nicotinic acetylcholine receptors (AChRs). To understand interactions of competitive antagonists at the atomic structural level, we studied binding of the curare derivatives d-tubocurarine (d-TC) and metocurine to AChBP using computational methods, mutagenesis, and ligand binding measurements. To account for protein flexibility, we used a 2-ns molecular dynamics simulation of AChBP to generate multiple snapshots of the equilibrated dynamic structure to which optimal docking orientations were determined. Our results predict a predominant docking orientation for both d-TC and metocurine, but unexpectedly, the bound orientations differ fundamentally for each ligand. At one subunit interface of AChBP, the side chain of Tyr-89 closely approaches a positively charged nitrogen in d-TC but is farther away from the equivalent nitrogen in metocurine, whereas, at the opposing interface, side chains of Trp-53 and Gln-55 closely approach the metocurine scaffold but not that of d-TC. The different orientations correspond to ∼170° rotation and ∼30° degree tilt of the curare scaffold within the binding pocket. Mutagenesis of binding site residues in AChBP, combined with measurements of ligand binding, confirms the different docking orientations. Thus structurally similar ligands can adopt distinct orientations at receptor binding sites, posing challenges for interpreting structure-activity relationships for many drugs.
AB - Acetylcholine-binding protein (AChBP) recently emerged as a prototype for relating structure to function of the ligand binding domain of nicotinic acetylcholine receptors (AChRs). To understand interactions of competitive antagonists at the atomic structural level, we studied binding of the curare derivatives d-tubocurarine (d-TC) and metocurine to AChBP using computational methods, mutagenesis, and ligand binding measurements. To account for protein flexibility, we used a 2-ns molecular dynamics simulation of AChBP to generate multiple snapshots of the equilibrated dynamic structure to which optimal docking orientations were determined. Our results predict a predominant docking orientation for both d-TC and metocurine, but unexpectedly, the bound orientations differ fundamentally for each ligand. At one subunit interface of AChBP, the side chain of Tyr-89 closely approaches a positively charged nitrogen in d-TC but is farther away from the equivalent nitrogen in metocurine, whereas, at the opposing interface, side chains of Trp-53 and Gln-55 closely approach the metocurine scaffold but not that of d-TC. The different orientations correspond to ∼170° rotation and ∼30° degree tilt of the curare scaffold within the binding pocket. Mutagenesis of binding site residues in AChBP, combined with measurements of ligand binding, confirms the different docking orientations. Thus structurally similar ligands can adopt distinct orientations at receptor binding sites, posing challenges for interpreting structure-activity relationships for many drugs.
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U2 - 10.1074/jbc.M301151200
DO - 10.1074/jbc.M301151200
M3 - Article
C2 - 12682067
AN - SCOPUS:0038603859
SN - 0021-9258
VL - 278
SP - 23020
EP - 23026
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 25
ER -