Yuji Tsuji

Structural basis of glutamate recognition by a dimeric metabotropic glutamate receptor.

The metabotropic glutamate receptors (mGluRs) are key receptors in the modulation of excitatory synaptic transmission in the central nervous system. Here we have determined three different crystal structures of the extracellular ligand-binding region of mGluR1—in a complex with glutamate and in two unliganded forms. They all showed disulphide-linked homodimers, whose ‘active’ and ‘resting’ conformations are modulated through the dimeric interface by a packed α-helical structure. The bi-lobed protomer architectures flexibly change their domain arrangements to form an ‘open’ or ‘closed’ conformation. The structures imply that glutamate binding stabilizes both the ‘active’ dimer and the ‘closed’ protomer in dynamic equilibrium. Movements of the four domains in the dimer are likely to affect the separation of the transmembrane and intracellular regions, and thereby activate the receptor. This scheme in the initial receptor activation could be applied generally to G-protein-coupled neurotransmitter receptors that possess extracellular ligand-binding sites.

Penetration of Magnetospheric Electric Fields to the Low Latitude Ionosphere During Storm/Substorms

Penetration of the magnetospheric electric fields to low latitude ionosphere is examined using magnetometer data from high latitude to the dip equator during substorms and geomagnetic storms. To detect the penetration electric fields, we analyzed magnetic disturbances at the dip equator, subtracted by those at low latitude (DP2). During substorm growth phase, the DP2 currents are enhanced by the dawn-to-dusk convection electric field, which are supplied by the Region-1 field-aligned currents (R1 FACs) via the mid and low latitude ionosphere. On the other hand, the DP2 currents decrease significantly during the substorm expansion, superposed by reversed currents flowing from the R2 FACs. In particular, when the IMF turns northward during the substorm, the DP2 currents change to the counterelectrojet (CEJ), i.e., overshielding currents at the dip equator. During the storm main phase, the DP2 currents are very much intensified by the enhanced convection electric field. However, the DP2 currents change to the CEJ at the beginning of the storm recovery phase. The overshielding electric field as well as the convection electric field causes dramatic changes in the low latitude ionosphere.