title: Transport dynamics in a glutamate transporter homologue.
abstract: Glutamate transporters are integral membrane proteins that catalyse neurotransmitter uptake from the synaptic cleft into the cytoplasm of glial cells and neurons. Their mechanism of action involves transitions between extracellular (outward)-facing and intracellular (inward)-facing conformations, whereby substrate binding sites become accessible to either side of the membrane. This process has been proposed to entail transmembrane movements of three discrete transport domains within a trimeric scaffold. Using single-molecule fluorescence resonance energy transfer (smFRET) imaging, we have directly observed large-scale transport domain movements in a bacterial homologue of glutamate transporters. We find that individual transport domains alternate between periods of quiescence and periods of rapid transitions, reminiscent of bursting patterns first recorded in single ion channels using patch-clamp methods. We propose that the switch to the dynamic mode in glutamate transporters is due to separation of the transport domain from the trimeric scaffold, which precedes domain movements across the bilayer. This spontaneous dislodging of the substrate-loaded transport domain is approximately 100-fold slower than subsequent transmembrane movements and may be rate determining in the transport cycle.
authors.affiliation: Department of Physiology and Biophysics, Weill Cornell Medical College, 1300 York Avenue, New York, New York 10064, USA.
authors.forename: Nurunisa
authors.initials: N
authors.lastname: Akyuz
authors.forename: Roger B
authors.initials: RB
authors.lastname: Altman
authors.forename: Scott C
authors.initials: SC
authors.lastname: Blanchard
authors.forename: Olga
authors.initials: O
authors.lastname: Boudker
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001224:Aspartic Acid / Q000737:chemistry; D001692:Biological Transport; D031541:Fluorescence Resonance Energy Transfer; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D043902:Pyrococcus horikoshii / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000737:chemistry
chemical_list: D027322:Amino Acid Transport System X-AG; D001224:Aspartic Acid; D012964:Sodium