抄録
We previously reported that the metabotropic glutamate receptor1α (mGluR1α) can be activated not only by glutamate but also by polyvalent cations such as Ca2+ and Gd3+, and has been working on the functional regulation and structure-function relationship of mGluR1α. The dimeric conformation of mGluR1α is a key determinant of the downstream signaling, since crystallographic analysis has shown that glutamate stabilizes the active state of the dimeric conformation of the extracellular domain. However, the conformational change of the cytoplasmic domain remains unknown, which is critical for the interaction with GTP binding proteins. We investigated the ligand-induced dynamic conformational changes of the cytoplasmic domain by analyzing the fluorescence resonance energy transfer (FRET) signal of mGluR1α labeled with fluorescent protein(s), obtained from the plasma membrane where ligands interact with mGluR1α, using a total internal reflection field microscopy system. Upon glutamate application, the intersubunit FRET efficiency between the second cytoplasmic loops was increased whereas that between the first loops was decreased. In contrast, the intrasubunit FRET efficiency was not changed. The effect was dependent on glutamate concentration, inhibited by mGluR1α antagonists and reproduced by Ca2+ and Gd3+, which are known to activate mGluR1α. We therefore conclude that ligand-induced rearrangement of the extracellular dimeric conformation leads to intracellular dimeric rearrangement without altering the respective monomeric conformations. [Jpn J Physiol 55 Suppl:S30 (2005)]
