Crystal Structure of the Monomeric Extracellular Domain of ?9 Nicotinic Receptor Subunit in Complex With ?-Conotoxin RgIA: Molecular Dynamics Insights Into RgIA Binding to ?9?10 Nicotinic Receptors.

ABSTRACT: The ?9 subunit of nicotinic acetylcholine receptors (nAChRs) exists mainly in heteropentameric assemblies with ?10. Accumulating data indicate the presence of three different binding sites in ?9?10 nAChRs: the ?9(+)/?9(-), the ?9(+)/?10(-), and the ?10(+)/?9(-). The major role of the principal (+) side of the extracellular domain (ECD) of ?9 subunit in binding of the antagonists methyllylcaconitine and ?-bungarotoxin was shown previously by the crystal structures of the monomeric ?9-ECD with these molecules. Here we present the 2.26-Å resolution crystal structure of ?9-ECD in complex with ?-conotoxin (?-Ctx) RgIA, a potential drug for chronic pain, the first structure reported for a complex between an nAChR domain and an ?-Ctx. Superposition of this structure with those of other ?-Ctxs bound to the homologous pentameric acetylcholine binding proteins revealed significant similarities in the orientation of bound conotoxins, despite the monomeric state of the ?9-ECD. In addition, ligand-binding studies calculated a binding affinity of RgIA to the ?9-ECD at the low micromolar range. Given the high identity between ?9 and ?10 ECDs, particularly at their (+) sides, the presented structure was used as template for molecular dynamics simulations of the ECDs of the human ?9?10 nAChR in pentameric assemblies. Our results support a favorable binding of RgIA at ?9(+)/?9(-) or ?10(+)/?9(-) rather than the ?9(+)/?10(-) interface, in accordance with previous mutational and functional data.

SUBMITTER: Zouridakis M 

PROVIDER: S-EPMC6504684 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature