Dokument: Transport dynamics in secondary active glutamate transporters
| Titel: | Transport dynamics in secondary active glutamate transporters | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=61999 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20230405-114939-4 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Groß-Esser, Felix [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Fahlke, Christoph [Gutachter] Prof. Dr. Gohlke, Holger [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 570 Biowissenschaften; Biologie | |||||||
| Beschreibung: | Clearance of glutamate from the synaptic cleft is a vital component of synaptic sig-
nal transmission. Excitatory amino acid transporters (EAATs) are secondary active transporters and feature rapid binding of glutamate and consequent transport into neurons and glial cells surrounding the synaptic cleft. They actively modulate and terminate synaptic signal transmission and keep extracellular glutamate concentra- tion below neurotoxic levels. Under physiological conditions, glutamate flux is cell inward but can be reversed under nonphysiological conditions, including pathological conditions like ischemic, hemorrhagic stroke or malign mutations. Pathological con- ditions can lead to high glutamate concentrations in the extracellular space, which causes glutamate excitotoxicity due to overstimulation of excitatory synapses, further escalating these life-threatening conditions. This causality makes the ability to mod- ulate the activity of EAATs highly desirable. EAATs transport glutamate against its gradient by cotransport of three sodium ions, one proton and counter transport of a single potassium ion along their gradients. By exploiting the energy stored in these gradients, EAATs can maintain a glutamate gra- dient with nanomolar concentration extracellular and millimolar values intracellular, with no need for a primary energy source. Additionally, they feature an anion-selective channel which is chloride conductive under glutamate transport conditions. Recently, progress has been made in understanding the binding and release of lig- ands and the associated conformational changes required. This was the result of com- bining structural data from X-ray crystallography, cryogenic electron microscopy and molecular dynamic simulations. X-ray crystallographic structures of EAAT1 and the close relative neutral amino acid transporter ASCT2 as well as archaebacterial homo- logue glutamate transporters (Glt) GltPh and GltTk were made available over the last 17 years. Notably, those obtained using GltPh exhibit large conformational diversity, including conformations in the two end states and multiple putative intermediates.Based on the published structures, an elevator-like movement of the transport domain relative to the trimerization domain was postulated, which allows the trans- port domain to switch between two distinct conformations, outward-facing (OFC) and inward-facing (IFC). This mechanism is a variant of the alternating access mechanism and requires, at least, vertical translation across the membrane and rotation of the transport domain. During this translational-rotational motion, the bound ligand is moved through the lipid bilayer and accessibility of the binding site is switched. This mechanism has been initially described for the prototypical elevator-like aspartate transporter GltPh , but in the following years, numerous transporters were found to operate according to this mechanism. For the published intermediates, their location in the conformational landscape and relevance are still up for debate. In particular, understanding of the formation and physiological role of the anion channel, forming during transport, is lacking. To investigate the conformational changes required for the physiological OFC to IFC translocation of a fully bound GltPh protomer, the “accelerated weight histogram” (AWH) method was combined with Markov state modeling. The complete transformational change required for the OFC-IFC transition was cap- tured and the elevator-like mechanism was characterized as a multistep process. This includes formation of the anion pore, which is not an obligatory step during transloca- tion. A possible influence of the lipid bilayer on transport dynamics and pore formation was found by comparison of asymmetric trimers. Additionally, a previously uncharted region in the conformational landscape was found, structurally similar to the IFC but featuring a more accessible binding site. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät | |||||||
| Dokument erstellt am: | 05.04.2023 | |||||||
| Dateien geändert am: | 05.04.2023 | |||||||
| Promotionsantrag am: | 02.03.2022 | |||||||
| Datum der Promotion: | 19.08.2022 |
