M. Safferling et al., First images of a glutamate receptor ion channel: Oligomeric state and molecular dimensions of GluRB homomers, BIOCHEM, 40(46), 2001, pp. 13948-13953
We have expressed, purified, and characterized glutamate receptor ion chann
els (GluR) assembled as homomers of the subunit GluRB. For the first time,
single-milligram quantities of biochemically homogeneous GluR have been obt
ained. The protein exhibits the expected pharmacological profile and a high
specific activity for ligand binding. Density-gradient centrifugation reve
als a uniform oligomeric assembly and a molecular mass suggesting that the
channel is a tetramer. On the basis of electron microscopic images, the rec
eptor 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 contr
ibute to formation of the ion-conducting pathway of the channel. The channe
l dimensions are consistent with an overall 2-fold symmetric assembly, sugg
esting that the tetrameric receptor may be a dimer of dimers.