文摘
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 pharmacologicalprofile and a high specific activity for ligand binding. Density-gradient centrifugation reveals a uniformoligomeric assembly and a molecular mass suggesting that the channel is a tetramer. On the basis ofelectron microscopic images, the receptor appears to form an elongated structure that is visualized inseveral orientations. The molecular dimensions of the molecule are approximately 11 × 14 × 17 nm, andsolvent-accessible features can be seen; these may contribute to formation of the ion-conducting pathwayof the channel. The channel dimensions are consistent with an overall 2-fold symmetric assembly, suggestingthat the tetrameric receptor may be a dimer of dimers.
