The ligand-binding domain of the kainate subtype KA2 of ionotropic glutamate receptors, a member of the type 2 periplasmic-binding fold protein superfamily.
This group contains the ligand-binding domain of the KA2 subunit of kainate receptor. While this ligand-binding domain is structurally homologous to the periplasmic binding fold type II superfamily, the N_terminal domain of kainate receptors belongs to the periplasmic-binding fold type I. There are five types of kainate receptors, GluR5, GluR6, GluR7, KA1, and KA2, which are structurally similar to AMPA and NMDA subunits of ionotropic glutamate receptors. KA1 and KA2 subunits can only form functional receptors with one of the GluR5-7 subunits. Moreover, GluR5-7 can also form functional homomeric receptor channels activated by kainate and glutamate when expressed in heterologous systems. Kainate receptors are involved in excitatory neurotransmission by activating postsynaptic receptors and in inhibitory neurotransmission by modulating release of the inhibitory neurotransmitter GABA through a presynaptic mechanism. Kainate receptors are closely related to AMAP receptors. In contrast of AMPA receptors, kainate receptors play only a minor role in signaling at synapses and their function is not well defined.
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