National Institutes of Health/National Institute of Neurological Disorders and Stroke (NIH/NINDS)
R37NS085318
United States
Citation
Journal: bioRxiv / Year: 2024 Title: Structural basis of the excitatory amino acid transporter 3 substrate recognition. Authors: Biao Qiu / Olga Boudker / Abstract: Excitatory amino acid transporters (EAATs) reside on cell surfaces and uptake substrates, including L-glutamate, L-aspartate, and D-aspartate, using ion gradients. Among five EAATs, EAAT3 is the only ...Excitatory amino acid transporters (EAATs) reside on cell surfaces and uptake substrates, including L-glutamate, L-aspartate, and D-aspartate, using ion gradients. Among five EAATs, EAAT3 is the only isoform that can efficiently transport L-cysteine, a substrate for glutathione synthesis. Recent work suggests that EAAT3 also transports the oncometabolite R-2-hydroxyglutarate (R-2HG). Here, we examined the structural basis of substrate promiscuity by determining the cryo-EM structures of EAAT3 bound to different substrates. We found that L-cysteine binds to EAAT3 in thiolate form, and EAAT3 recognizes different substrates by fine-tuning local conformations of the coordinating residues. However, using purified human EAAT3, we could not observe R-2HG binding or transport. Imaging of EAAT3 bound to L-cysteine revealed several conformational states, including an outward-facing state with a semi-open gate and a disrupted sodium-binding site. These structures illustrate that the full gate closure, coupled with the binding of the last sodium ion, occurs after substrate binding. Furthermore, we observed that different substrates affect how the transporter distributes between a fully outward-facing conformation and intermediate occluded states on a path to the inward-facing conformation, suggesting that translocation rates are substrate-dependent.
Number selected: 4180263 Details: This is the number of trimer particle from the image.
Startup model
Type of model: NONE / Details: ab-initio
Final reconstruction
Number classes used: 3 / Applied symmetry - Point group: C1 (asymmetric) / Resolution.type: BY AUTHOR / Resolution: 2.58 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: cryoSPARC (ver. 3) Details: This is number of monomer from C3 expanded particles Number images used: 307042
Initial angle assignment
Type: MAXIMUM LIKELIHOOD / Software - Name: cryoSPARC (ver. 3)
Final angle assignment
Type: MAXIMUM LIKELIHOOD / Software - Name: cryoSPARC (ver. 3)
Final 3D classification
Number classes: 20 / Software - Name: RELION (ver. 3) Details: This is a local classification for monomers on expanded particles.
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