title: Local constraints in either the GluN1 or GluN2 subunit equally impair NMDA receptor pore opening.
abstract: The defining functional feature of N-methyl-d-aspartate (NMDA) receptors is activation gating, the energetic coupling of ligand binding into opening of the associated ion channel pore. NMDA receptors are obligate heterotetramers typically composed of glycine-binding GluN1 and glutamate-binding GluN2 subunits that gate in a concerted fashion, requiring all four ligands to bind for subsequent opening of the channel pore. In an individual subunit, the extracellular ligand-binding domain, composed of discontinuous polypeptide segments S1 and S2, and the transmembrane channel-forming domain, composed of M1-M4 segments, are connected by three linkers: S1-M1, M3-S2, and S2-M4. To study subunit-specific events during pore opening in NMDA receptors, we impaired activation gating via intrasubunit disulfide bonds connecting the M3-S2 and S2-M4 in either the GluN1 or GluN2A subunit, thereby interfering with the movement of the M3 segment, the major pore-lining and channel-gating element. NMDA receptors with gating impairments in either the GluN1 or GluN2A subunit were dramatically resistant to channel opening, but when they did open, they showed only a single-conductance level indistinguishable from wild type. Importantly, the late gating steps comprising pore opening to its main long-duration open state were equivalently affected regardless of which subunit was constrained. Thus, the NMDA receptor ion channel undergoes a pore-opening mechanism in which the intrasubunit conformational dynamics at the level of the ligand-binding/transmembrane domain (TMD) linkers are tightly coupled across the four subunits. Our results further indicate that conformational freedom of the linkers between the ligand-binding and TMDs is critical to the activation gating process.
authors: Graduate Program in Neuroscience, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
authors: Iehab
authors: I
authors: Talukder
authors: Lonnie P
authors: LP
authors: Wollmuth
mesh_terms: D000818:Animals; D001665:Binding Sites; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018698:Glutamic Acid / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008024:Ligands; D008958:Models, Molecular; D009865:Oocytes / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014981:Xenopus
chemical_list: D008024:Ligands; D021122:Protein Subunits; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D005998:Glycine