title: Asynchronous movements prior to pore opening in NMDA receptors.
abstract: Glutamate-gated ion channels embedded within the neuronal membrane are the primary mediators of fast excitatory synaptic transmission in the CNS. The ion channel of these glutamate receptors contains a pore-lining transmembrane M3 helix surrounded by peripheral M1 and M4 helices. In the NMDA receptor subtype, opening of the ion channel pore, mediated by displacement of the M3 helices away from the central pore axis, occurs in a highly concerted fashion, but the associated temporal movements of the peripheral helices are unknown. To address the gating dynamics of the peripheral helices, we constrained the relative movements of the linkers that connect these helices to the ligand-binding domain using engineered cross-links, either within (intra-GluN1 or GluN2A) or between subunits. Constraining the peripheral linkers in any manner dramatically curtailed channel opening, highlighting the requirement for rearrangements of these peripheral structural elements for efficient gating to occur. However, the magnitude of this gating effect depended on the specific subunit being constrained, with the most dramatic effects occurring when the constraint was between subunits. Based on kinetic and thermodynamic analysis, our results suggest an asynchrony in the displacement of the peripheral linkers during the conformational and energetic changes leading to pore opening. Initially there are large-scale rearrangements occurring between the four subunits. Subsequently, rearrangements occur within individual subunits, mainly GluN2A, leading up to or in concert with pore opening. Thus, the conformational changes induced by agonist binding in NMDA receptors converge asynchronously to permit pore opening.
authors.affiliation: Graduate Program in Neuroscience, Stony Brook University, Stony Brook, New York 11794-5230, USA.
authors.forename: Rashek
authors.initials: R
authors.lastname: Kazi
authors.forename: Quan
authors.initials: Q
authors.lastname: Gan
authors.forename: Iehab
authors.initials: I
authors.lastname: Talukder
authors.forename: Michael
authors.initials: M
authors.lastname: Markowitz
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Salussolia
authors.forename: Lonnie P
authors.initials: LP
authors.lastname: Wollmuth
mesh_terms: D000818:Animals; D001665:Binding Sites; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008958:Models, Molecular; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000737:chemistry / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D016194:Receptors, N-Methyl-D-Aspartate