Interaction of 5‐HT3R ligands with acetylcholine binding protein by surface plasmon resonance

Abstract

The field of Ligand Gated Ion Channels (LGIC) has benefited greatly over the last several years due to the discovery of the Acetylcholine Binding Protein (AChBP) from snail Lymnaea stagnalis and Aplysia californica. Studies have utilized docking simulations, crystal structure and radio ligand binding data of the AChBP to better understand the function of ligand binding. The AChBP has also been used to characterize other cys‐loop super family LIGC including the serotonin type 3 receptor (5‐HT3R). Although homology models for the AChBP and 5‐HT3R exist there is a lack of information describing how 5‐HT ligands interact with the AChBP.Understanding how 5‐HTR ligands interact with the AChBP binding pocket is crucial knowledge for comparing the functional relationship between AChBP and 5‐HT3R ligand binding site. The goal of this work was to obtain binding data for 5‐HT3R ligands using radio‐ligand binding experiments and Surface Plasmon Resonance (SPR) as well as confirm validity of 5‐HT3R antagonist binding models based on AChBP. We evaluated the binding of 5‐HT3R agonists, partial agonists and antagonists to the AChBP. Results showed binding affinities for 5‐HT3R agonist were 500–30,000 times lower on the AChBP compared to 5‐HT3R. Binding affinities for 5‐HT3R antagonists were 2–30 lower on the AChBP compared to the 5‐HT3R (>KD). The interaction of antagonists to AChBP is similar to those present in 5‐HT3R while those residues interacting with agonists show less homology. Our docking studies supported these conclusions.