title: Small-scale molecular motions accomplish glutamate uptake in human glutamate transporters.
abstract: Glutamate transporters remove glutamate from the synaptic cleft to maintain efficient synaptic communication between neurons and to prevent glutamate concentrations from reaching neurotoxic levels. Glutamate transporters play an important role in ischemic neuronal death during stroke and have been implicated in epilepsy and amytropic lateral sclerosis. However, the molecular structure and the glutamate-uptake mechanism of these transporters are not well understood. The most recent models of glutamate transporters have three or five subunits, each with eight transmembrane domains, and one or two membrane-inserted loops. Here, using fluorescence resonance energy transfer (FRET) analysis, we have determined the relative position of the extracellular regions of these domains. Our results are consistent with a trimeric glutamate transporter with a large (>45 A) extracellular vestibule. In contrast to other transport proteins, our FRET measurements indicate that there are no large-scale motions in glutamate transporters and that glutamate uptake is accompanied by relatively small motions around the glutamate-binding sites. The large extracellular vestibule and the small-scale conformational changes could contribute to the fast kinetics predicted for glutamate transporters. Furthermore, we show that, despite the multimeric nature of glutamate transporters, the subunits function independently.
authors.affiliation: Neurological Sciences Institute, Oregon Health and Science University, Beaverton, Oregon 97006, USA.
authors.forename: Hans P
authors.initials: HP
authors.lastname: Koch
authors.forename: H Peter
authors.initials: HP
authors.lastname: Larsson
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D000818:Animals; D016880:Anisotropy; D003545:Cysteine / Q000737:chemistry; D005260:Female; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes / Q000737:chemistry; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008301:Maleimides / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D009038:Motion; D016297:Mutagenesis, Site-Directed; D009865:Oocytes; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000502:physiology; D012235:Rhodamines / Q000737:chemistry; D013329:Structure-Activity Relationship; D027981:Symporters / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D014982:Xenopus laevis
chemical_list: C504424:Alexa Fluor 488 C5-maleimide; D027322:Amino Acid Transport System X-AG; D005456:Fluorescent Dyes; D050491:Glutamate Plasma Membrane Transport Proteins; D008301:Maleimides; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D012235:Rhodamines; D027981:Symporters; D018698:Glutamic Acid; D003545:Cysteine
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