Asymmetry and Ion Selectivity Properties of Bacterial Channel NaK Mutants Derived from Ionotropic Glutamate Receptors |
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| Affiliation: | 1. Institute of Biology, Cellular Biophysics, Humboldt Universität zu Berlin, 10115 Berlin, Germany;2. NeuroCure, Charité Universitätsmedizin, 10117 Berlin, Germany;3. Leibniz Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany;4. Institute of Chemistry, Department of Chemistry, Technische Universität Berlin, 10623 Berlin, Germany;1. CIPMM, Universität des Saarlandes, Homburg, Saarland, Germany;2. Institute of Biology, Cellular Biophysics, Humboldt Universität zu Berlin, 10115 Berlin, Germany;3. Leibniz Forschungsinstitut für Molekulare Pharmakologie (FMP), 13125 Berlin, Germany;4. NeuroCure, Charité Universitätsmedizin, 10117 Berlin, Germany;1. Shanghai Applied Radiation Institute, Shanghai University, Shanghai 200444, PR China;2. School of Environmental and Chemical Engineering, Shanghai University, Shanghai 201800, PR China;1. Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168th Street, New York, NY 10032, USA;2. Department of Physiology and Cellular Biophysics, Columbia University Irving Medical Center, 630 West 168th Street, New York, NY 10032, USA;1. Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province, Southwest Petroleum University, Chengdu, Sichuan 610500, China;2. College of Chemistry and Chemical Engineering, Southwest Petroleum University, 8 Xindu Avenue, Chengdu, Sichuan 610500, China;3. Research Institute of Industrial Hazardous Waste Disposal and Resource Utilization, Southwest Petroleum University, Chengdu, Sichuan 610500, China;4. Tianfu Yongxing Laboratory, Chengdu, China;1. Department of Biology, College of William and Mary, Williamsburg, VA, U.S.A.;2. Department of Biology, Lycoming College, Williamsport, PA, U.S.A.;1. Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM), México City 04510, Mexico;2. Sección de Bioelectrónica, CINVESTAV-IPN, México City 07360, Mexico |
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| Abstract: | Ionotropic glutamate receptors are ligand-gated cation channels that play essential roles in the excitatory synaptic transmission throughout the central nervous system. A number of open-pore structures of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic-acid (AMPA)-type glutamate receptors became available recently by cryo-electron microscopy (cryo-EM). These structures provide valuable insights into the conformation of the selectivity filter (SF), the part of the ion channel that determines the ion selectivity. Nonetheless, due to the moderate resolution of the cryo-EM structures, detailed information such as ion occupancy of monovalent and divalent cations as well as positioning of the side-chains in the SF is still missing. Here, in an attempt to obtain high-resolution information about glutamate receptor SFs, we incorporated partial SF sequences of the AMPA and kainate receptors into the bacterial tetrameric cation channel NaK, which served as a structural scaffold. We determined a series of X-ray structures of NaK-CDI, NaK-SDI and NaK-SELM mutants at 1.42–2.10 Å resolution, showing distinct ion occupation of different monovalent cations. Molecular dynamics (MD) simulations of NaK-CDI indicated the channel to be conductive to monovalent cations, which agrees well with our electrophysiology recordings. Moreover, previously unobserved structural asymmetry of the SF was revealed by the X-ray structures and MD simulations, implying its importance in ion non-selectivity of tetrameric cation channels. |
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| Keywords: | crystallography molecular dynamics bilayer ion channel |
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