title: First images of a glutamate receptor ion channel: oligomeric state and molecular dimensions of GluRB homomers.
abstract: We have expressed, purified, and characterized glutamate receptor ion channels (GluR) assembled as homomers of the subunit GluRB. For the first time, single-milligram quantities of biochemically homogeneous GluR have been obtained. The protein exhibits the expected pharmacological profile and a high specific activity for ligand binding. Density-gradient centrifugation reveals a uniform oligomeric assembly and a molecular mass suggesting that the channel is a tetramer. On the basis of electron microscopic images, the receptor appears to form an elongated structure that is visualized in several orientations. The molecular dimensions of the molecule are approximately 11 x 14 x 17 nm, and solvent-accessible features can be seen; these may contribute to formation of the ion-conducting pathway of the channel. The channel dimensions are consistent with an overall 2-fold symmetric assembly, suggesting that the tetrameric receptor may be a dimer of dimers.
authors.affiliation: Ion Channel Structure Research Group, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Safferling
authors.forename: W
authors.initials: W
authors.lastname: Tichelaar
authors.forename: G
authors.initials: G
authors.lastname: Kümmerle
authors.forename: A
authors.initials: A
authors.lastname: Jouppila
authors.forename: A
authors.initials: A
authors.lastname: Kuusinen
authors.forename: K
authors.initials: K
authors.lastname: Keinänen
authors.forename: D R
authors.initials: DR
authors.lastname: Madden
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure; D007700:Kinetics; D008024:Ligands; D008854:Microscopy, Electron; D051381:Rats; D018091:Receptors, AMPA / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000648:ultrastructure; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification / Q000648:ultrastructure; D018411:Spodoptera / Q000235:genetics
chemical_list: D007473:Ion Channels; D008024:Ligands; D018091:Receptors, AMPA; D011994:Recombinant Proteins; C115953:glutamate receptor type B