Assembly of a π-π Stack of ligands in the binding site of an acetylcholine-binding protein

Acetylcholine-binding protein is a water-soluble homologue of the extracellular ligand-binding domain of cys-loop receptors. It is used as a structurally accessible prototype for studying ligand binding to these pharmaceutically important pentameric ion channels, in particular to nicotinic acetylcholine receptors, due to conserved binding site residues present at the interface between two subunits. Here we report that an aromatic conjugated small molecule binds acetylcholine-binding protein in an ordered π-π stack of three identical molecules per binding site, two parallel and one antiparallel. Acetylcholine-binding protein stabilizes the assembly of the stack by aromatic contacts. Thanks to the plasticity of its ligand-binding site, acetylcholine-binding protein can accommodate the formation of aromatic stacks of different size by simple loop repositioning and minimal adjustment of the interactions. This type of supramolecular binding provides a novel paradigm in drug design. © 2013 Macmillan Publishers Limited. All rights reserved

Insight in nAChR subtype selectivity from AChBP crystal structures

International audienceNicotinic acetylcholine receptors (nAChRs) display a broad variety of subtypes, which in turn present a complex subcellular and regional expression pattern in the brain, as well as a specific pharmacological profile. The association of these nAChRs with different types of brain disease has turned them into interesting drug targets for the treatment of Alzheimer's disease or schizophrenia, or for anti-smoking compounds among others. In the same way, muscle-type nAChRs present at neuromuscular junctions are also being targeted by muscle relaxants. However, to date no high-resolution structural data is available on functional pentameric forms of membrane bound nicotinic receptors. Therefore, characterization of the selectivity profiles of different nicotinic receptor subtypes, enabling efficient drug design, is a serious issue. Over the last eight years various high resolution structures of acetylcholine binding protein (AChBP), which is homologous to the extracellular ligand binding domain of the nicotinic acetylcholine receptor, have been obtained. AChBPs in complex with different ligands have provided detailed insight into the neurotransmitter binding site of nicotinic acetylcholine receptors. We present here the various efforts towards rationalizing subtype specificity in these receptors through the structural studies of acetylcholine binding protein-ligand complexes

Assembly of a π–π stack of ligands in the binding site of an acetylcholine-binding protein

Acetylcholine-binding protein is a water-soluble homologue of the extracellular ligand-binding domain of cys-loop receptors. It is used as a structurally accessible prototype for studying ligand binding to these pharmaceutically important pentameric ion channels, in particular to nicotinic acetylcholine receptors, due to conserved binding site residues present at the interface between two subunits. Here we report that an aromatic conjugated small molecule binds acetylcholine-binding protein in an ordered π-π stack of three identical molecules per binding site, two parallel and one antiparallel. Acetylcholine-binding protein stabilizes the assembly of the stack by aromatic contacts. Thanks to the plasticity of its ligand-binding site, acetylcholine-binding protein can accommodate the formation of aromatic stacks of different size by simple loop repositioning and minimal adjustment of the interactions. This type of supramolecular binding provides a novel paradigm in drug design. © 2013 Macmillan Publishers Limited. All rights reserved

Acetylcholine binding protein (AChBP) as template for hierarchical in silico screening procedures to identify structurally novel ligands for the nicotinic receptors

Hierarchical in silico screening protocols against the agonist bound acetylcholine binding protein (AChBP) crystal structure were efficient in identifying novel chemotypes for AChBP and the human α7 receptor. Two hit structures were cocrystallized with AChBP revealing intermolecular cation-π interactions with loop C but lacking intermolecular hydrogen bonding. The compounds act as competitive α7 receptor antagonists and as non-competitive α4β2 receptor inhibitors. These results underline the usability of AChBP in structure-based in silico screening strategies in finding novel scaffolds for the α7 receptor, but also illustrates some limitations of using AChBP as bait to find competitive α4β2 receptor ligands and α7 receptor agonists. © 2011 Elsevier Ltd. All rights reserved

Fragment growing induces conformational changes in acetylcholine-binding protein: A structural and thermodynamic analysis

Optimization of fragment hits toward high-affinity lead compounds is a crucial aspect of fragment-based drug discovery (FBDD). In the current study, we have successfully optimized a fragment by growing into a ligand-inducible subpocket of the binding site of acetylcholine-binding protein (AChBP). This protein is a soluble homologue of the ligand binding domain (LBD) of Cys-loop receptors. The fragment optimization was monitored with X-ray structures of ligand complexes and systematic thermodynamic analyses using surface plasmon resonance (SPR) biosensor analysis and isothermal titration calorimetry (ITC). Using site-directed mutagenesis and AChBP from different species, we find that specific changes in thermodynamic binding profiles, are indicative of interactions with the ligand-inducible subpocket of AChBP. This study illustrates that thermodynamic analysis provides valuable information on ligand binding modes and is complementary to affinity data when guiding rational structure- and fragment-based discovery approaches