First images of a glutamate receptor ion channel: oligomeric state and molecular dimensions of GluRB homomers. |
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Authors: | M Safferling W Tichelaar G Kümmerle A Jouppila A Kuusinen K Kein?nen D R Madden |
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Institution: | Ion Channel Structure Research Group, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany. |
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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. |
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