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Divergent mechanisms of steroid inhibition in the human ρ1 GABA(A) receptor

Affiliations
  • 1Dept. of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden.
  • 2Dept. of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden.
  • 3Dept. of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden. rebecca.howard@dbb.su.se.
  • 4Dept. of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden. rebecca.howard@dbb.su.se.
  • 5Dept. of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden. erik.lindahl@dbb.su.se.
  • 6Dept. of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden. erik.lindahl@dbb.su.se.

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September 6, 2024

Abstract

ρ-type γ-aminobutyric acid-A (GABA) receptors are widely distributed in the retina and brain, and are potential drug targets for the treatment of visual, sleep and cognitive disorders. Endogenous neuroactive steroids including β-estradiol and pregnenolone sulfate negatively modulate the function of ρ1 GABA receptors, but their inhibitory mechanisms are not clear. By combining five cryo-EM structures with electrophysiology and molecular dynamics simulations, we characterize binding sites and negative modulation mechanisms of β-estradiol and pregnenolone sulfate at the human ρ1 GABA receptor. β-estradiol binds in a pocket at the interface between extracellular and transmembrane domains, apparently specific to the ρ subfamily, and disturbs allosteric conformational transitions linking GABA binding to pore opening. In contrast, pregnenolone sulfate binds inside the pore to block ion permeation, with a preference for activated structures. These results illuminate contrasting mechanisms of ρ1 inhibition by two different neuroactive steroids, with potential implications for subtype-specific gating and pharmacological design.

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