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Structural basis for a bimodal allosteric mechanism of general anesthetic modulation in pentameric ligand-gated ion channels
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Science for Life Laboratory (SciLifeLab).ORCID iD: 0000-0003-2049-3378
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Science for Life Laboratory (SciLifeLab).ORCID iD: 0000-0003-3224-4547
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2018 (English)In: Cell reports, ISSN 2211-1247, E-ISSN 2211-1247Article in journal (Refereed) Accepted
Abstract [en]

Ion channel modulation by general anesthetics is a vital pharmacological process with implications for receptor biophysics and drug development. Functional studies have implicated conserved sites of both potentiation and inhibition in pentameric ligand-gated ion channels, but a detailed structural mechanism for these bimodal effects is lacking[1] . The prokaryotic model protein GLIC recapitulates anesthetic modulation of human ion channels, and is accessible to structure determination in both apparent open and closed states. Here, we report ten X-ray structures and electrophysiological characterization of GLIC variants in the presence and absence of general anesthetics, including the surgical agent propofol. We show that general anesthetics can allosterically favor closed channels by binding in the pore, or favor open channels via various subsites in the transmembrane domain. Our results support an integrated, multi-site mechanism for allosteric modulation, and provide atomic details of both potentiation and inhibition by one of the most common general anesthetics.

Place, publisher, year, edition, pages
2018.
National Category
Biochemistry and Molecular Biology Structural Biology
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-154102OAI: oai:DiVA.org:su-154102DiVA, id: diva2:1190776
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2018-03-27
In thesis
1. Allosteric modulation of pentameric ligand-gated ion channels by general anesthetics
Open this publication in new window or tab >>Allosteric modulation of pentameric ligand-gated ion channels by general anesthetics
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Pentameric ligand-gated ion channels (pLGICs) are key components of fast synaptic transmission and are targets of neuroactive drugs such as benzodiazepines, alcohol and muscle relaxants. Although early theories of general anesthesia suggested non-specific lipid interaction as the mechanism of anesthetic action, it has now become evident that they too bind to pLGICs. While general anesthetics act as positive allosteric modulators on most anion-conducting pLGICs, they inhibit cation-conducting channels. A detailed structural mechanism of how such opposite allosteric effects emerge has yet to be presented.

This thesis investigates the structure-function relationship underlying the dynamics of channel activation and explores the mechanisms behind allosteric modulation by general anesthetics. Key model systems include the glutamate-gated chloride channel of C. elegans (GluCl) and the G. violaceus ligand-gated ion channel (GLIC), that show considerable structural homology to mammalian channel but with the added simplicity of homomeric assembly and accessibility to crystallization. Functional assessment is performed through recombinant expression of the channels in Xenopus oocytes, which are then used for two-electrode voltage clamp electrophysiology. These measurements are combined with recent advances in structure determination and computational simulations to propose structural mechanisms behind the functional effects.

In this thesis I present the exploration and validation of the crystallographic construct GluCl as a model system to explore fundamental questions of mammalian pLGIC function. Further studies contribute to the understanding of the basis of allosteric modulation by identifying responsible binding sites for both potentiation and inhibition by general anesthetics in GLIC and substantiate a structural mechanism for these effects. The studies also offer a link between receptor- and lipid-based theories of anesthesia, and demonstrate successful discovery of new lead compounds with general anesthetic properties using virtual screening. The thesis therefore makes a contribution to the fundamental understanding of allosteric modulation in pLGICs and builds on the basis for rational drug discovery.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2018
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-154106 (URN)978-91-7797-151-1 (ISBN)978-91-7797-152-8 (ISBN)
Public defence
2018-05-04, Magnéli Hall, Chemical Practice Laboratory, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Accepted. Paper 4: Manuscript.

Available from: 2018-04-11 Created: 2018-03-15 Last updated: 2018-04-09

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Howard, Rebecca J.Heusser, Stephanie A.Lindahl, Erik
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