Large domain movements through the lipid bilayer mediate substrate release and inhibition of glutamate transporters

Elife. 2020 Nov 6;9:e58417. doi: 10.7554/eLife.58417.

Abstract

Glutamate transporters are essential players in glutamatergic neurotransmission in the brain, where they maintain extracellular glutamate below cytotoxic levels and allow for rounds of transmission. The structural bases of their function are well established, particularly within a model archaeal homolog, sodium, and aspartate symporter GltPh. However, the mechanism of gating on the cytoplasmic side of the membrane remains ambiguous. We report Cryo-EM structures of GltPh reconstituted into nanodiscs, including those structurally constrained in the cytoplasm-facing state and either apo, bound to sodium ions only, substrate, or blockers. The structures show that both substrate translocation and release involve movements of the bulky transport domain through the lipid bilayer. They further reveal a novel mode of inhibitor binding and show how solutes release is coupled to protein conformational changes. Finally, we describe how domain movements are associated with the displacement of bound lipids and significant membrane deformations, highlighting the potential regulatory role of the bilayer.

Keywords: E. coli; GltPh; glutamate transporters; ion-coupled membrane transporters; membrane structure; molecular biophysics; structural biology.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Transport System X-AG / chemistry*
  • Amino Acid Transport System X-AG / genetics
  • Amino Acid Transport System X-AG / metabolism*
  • Archaeal Proteins / chemistry*
  • Archaeal Proteins / genetics
  • Archaeal Proteins / metabolism*
  • Biological Transport
  • Cryoelectron Microscopy
  • Glutamic Acid / chemistry
  • Glutamic Acid / metabolism
  • Kinetics
  • Lipid Bilayers / chemistry
  • Lipid Bilayers / metabolism
  • Models, Molecular
  • Protein Domains
  • Pyrococcus horikoshii / chemistry
  • Pyrococcus horikoshii / genetics
  • Pyrococcus horikoshii / metabolism*
  • Sodium / chemistry
  • Sodium / metabolism

Substances

  • Amino Acid Transport System X-AG
  • Archaeal Proteins
  • Lipid Bilayers
  • Glutamic Acid
  • Sodium