A Structural Rationale for N‐Methylbicuculline Acting as a Promiscuous Competitive Antagonist of Inhibitory Pentameric Ligand‐Gated Ion Channels. (12th February 2020)

• Record Type: Journal Article
• Authors: Jones, Mathew J.; Dawson, Alice; Hales, Tim G.; Hunter, William N.
• Is Part Of: Chembiochem. Volume 21:Number 10(2020)
• Page Start: 1526
• Page End: 1533
• Publication Date: 2020-02-12
• Subjects: acetylcholine-binding proteins -- alkaloids -- competitive antagonists -- crystal structures -- GABAA receptors -- glycine receptor; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pharmaceutical chemistry -- Periodicals; 572
• DOI: 10.1002/cbic.201900680
• Languages: English
• ISSNs: 1439-4227

Abstract

Abstract: Bicuculline, a valued chemical tool in neurosciences research, is a competitive antagonist of specific GABAA receptors and affects other pentameric ligand‐gated ion channels including the glycine, nicotinic acetylcholine and 5‐hydroxytryptamine type 3 receptors. We used a fluorescence‐quenching assay and isothermal titration calorimetry to record low‐micromolar dissociation constants for N ‐methylbicuculline interacting with acetylcholine‐binding protein and an engineered version called glycine‐binding protein (GBP), which provides a surrogate for the heteromeric interface of the extracellular domain of the glycine receptor (GlyR). The 2.4 Å resolution crystal structure of the GBP: N ‐methylbicuculline complex, sequence and structural alignments reveal similarities and differences between GlyR and the GABAA receptor–bicuculline interactions. N ‐methylbicuculline displays a similar conformation in different structures, but adopts distinct orientations enforced by interactions and steric blocks with key residues and plasticity in the binding sites. These features explain the promiscuous activity of bicuculline against the principal inhibitory pentameric ligand‐gated ion channels in the CNS. Abstract : Any which way? Binding data and the structure of an engineered acetylcholine‐binding protein with N ‐methylbicuculline, a promiscuous antagonist of pentameric ligand‐gated ion channels, are reported. The antagonist appears to adopt a similar conformation but different orientations in inhibitory glycine and GABAA receptors.