4p19
Closed, apo inward-facing state of the glutamate transporter homologue GltPh
Structural highlights
FunctionGLT_PYRHO Sodium-dependent, high-affinity amino acid transporter that mediates aspartate uptake (PubMed:17435767, PubMed:19380583, PubMed:17230192, Ref.11). Has only very low glutamate transport activity (PubMed:19380583, PubMed:17230192). Functions as a symporter that transports one amino acid molecule together with two or three Na(+) ions, resulting in electrogenic transport (PubMed:17435767, PubMed:19380583, Ref.11). Na(+) binding enhances the affinity for aspartate (PubMed:19380583, Ref.11). Mediates Cl(-) flux that is not coupled to amino acid transport; this avoids the accumulation of negative charges due to aspartate and Na(+) symport (PubMed:17435767). In contrast to mammalian homologs, transport does not depend on pH or K(+) ions (PubMed:19380583).[1] [2] [3] [PDB:4P19] Publication Abstract from PubMedMembrane transporters that clear the neurotransmitter glutamate from synapses are driven by symport of sodium ions and counter-transport of a potassium ion. Previous crystal structures of a homologous archaeal sodium and aspartate symporter showed that a dedicated transport domain carries the substrate and ions across the membrane. Here, we report new crystal structures of this homologue in ligand-free and ions-only bound outward- and inward-facing conformations. We show that after ligand release, the apo transport domain adopts a compact and occluded conformation that can traverse the membrane, completing the transport cycle. Sodium binding primes the transport domain to accept its substrate and triggers extracellular gate opening, which prevents inward domain translocation until substrate binding takes place. Furthermore, we describe a new cation-binding site ideally suited to bind a counter-transported ion. We suggest that potassium binding at this site stabilizes the translocation-competent conformation of the unloaded transport domain in mammalian homologues. Coupled ion binding and structural transitions along the transport cycle of glutamate transporters.,Verdon G, Oh S, Serio RN, Boudker O Elife. 2014 May 19:e02283. doi: 10.7554/eLife.02283. PMID:24842876[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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