(+)-Catharanthine potentiates the GABAA receptor by binding to a transmembrane site at the β(+)/α(-) interface near the TM2-TM3 loop

Hugo R. Arias, Cecilia M. Borghese, Allison L. Germann, Spencer R. Pierce, Alessandro Bonardi, Alessio Nocentini, Paola Gratteri, Thanvi M. Thodati, Natalie J. Lim, R. Adron Harris, Gustav Akk

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

(+)-Catharanthine, a coronaridine congener, potentiates the γ-aminobutyric acid type A receptor (GABAAR) and induces sedation through a non-benzodiazepine mechanism, but the specific site of action and intrinsic mechanism have not been defined. Here, we describe GABAAR subtype selectivity and location of the putative binding site for (+)-catharanthine using electrophysiological, site-directed mutagenesis, functional competition, and molecular docking experiments. Electrophysiological and in silico experiments showed that (+)-catharanthine potentiates the responses to low, subsaturating GABA at β2/3-containing GABAARs 2.4–3.5 times more efficaciously than at β1-containing GABAARs. The activity of (+)-catharanthine is reduced by the β2(N265S) mutation that decreases GABAAR potentiation by loreclezole, but not by the β3(M286C) or α1(Q241L) mutations that reduce receptor potentiation by R(+)-etomidate or neurosteroids, respectively. Competitive functional experiments indicated that the binding site for (+)-catharanthine overlaps that for loreclezole, but not those for R(+)-etomidate or potentiating neurosteroids. Molecular docking experiments suggested that (+)-catharanthine binds at the β(+)/α(-) intersubunit interface near the TM2-TM3 loop, where it forms H-bonds with β2-D282 (TM3), β2-K279 (TM2-TM3 loop), and β2-N265 and β2-R269 (TM2). Site-directed mutagenesis experiments supported the in silico results, demonstrating that the K279A and D282A substitutions, that lead to a loss of H-bonding ability of the mutated residue, and the N265S mutation, impair the gating efficacy of (+)-catharanthine. We infer that (+)-catharanthine potentiates the GABAAR through several H-bond interactions with a binding site located in the β(+)/α(-) interface in the transmembrane domain, near the TM2-TM3 loop, where it overlaps with loreclezole binding site.

Original languageEnglish
Article number114993
JournalBiochemical Pharmacology
Volume199
DOIs
StatePublished - May 2022
Externally publishedYes

Keywords

  • (+)-Catharanthine
  • Coronaridine congeners
  • Electrophysiology
  • Molecular docking
  • Molecular dynamics
  • Positive allosteric modulators

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