title: Crystal structure and dynamics of a lipid-induced potential desensitized-state of a pentameric ligand-gated channel.
abstract: Desensitization in pentameric ligand-gated ion channels plays an important role in regulating neuronal excitability. Here, we show that docosahexaenoic acid (DHA), a key ω-3 polyunsaturated fatty acid in synaptic membranes, enhances the agonist-induced transition to the desensitized state in the prokaryotic channel GLIC. We determined a 3.25 Å crystal structure of the GLIC-DHA complex in a potentially desensitized conformation. The DHA molecule is bound at the channel-periphery near the M4 helix and exerts a long-range allosteric effect on the pore across domain-interfaces. In this previously unobserved conformation, the extracellular-half of the pore-lining M2 is splayed open, reminiscent of the open conformation, while the intracellular-half is constricted, leading to a loss of both water and permeant ions. These findings, in combination with spin-labeling/EPR spectroscopic measurements in reconstituted-membranes, provide novel mechanistic details of desensitization in pentameric channels.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States.
authors.forename: Sandip
authors.identifier: http://orcid.org/0000-0003-4018-8020
authors.initials: S
authors.lastname: Basak
authors.affiliation: Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, United States.
authors.forename: Nicolaus
authors.initials: N
authors.lastname: Schmandt
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States.
authors.forename: Yvonne
authors.identifier: http://orcid.org/0000-0002-3938-8853
authors.initials: Y
authors.lastname: Gicheru
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States.
authors.forename: Sudha
authors.identifier: http://orcid.org/0000-0003-0722-2338
authors.initials: S
authors.lastname: Chakrapani
mesh_terms: D018360:Crystallography, X-Ray; D004281:Docosahexaenoic Acids / Q000737:chemistry* / Q000378:metabolism*; D058446:Ligand-Gated Ion Channels / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D058446:Ligand-Gated Ion Channels; D004281:Docosahexaenoic Acids
keywords: Cys-loop receptors; E. coli; allosteric modulation; biochemistry; biophysics; nanodiscs; site-directed spin labeling; structural biology