Kainate Receptors

The kainate receptor subfamily consists of five members that have been further subdivided into two classes based upon structural homology and functional characteristics. GluR5, GluR6, and GluR7 receptor subunits share a high degree of homology and are able to form functional channels when expressed in heterologous systems. The KA-1 and KA-2 receptors are unable to form functional channels on their own, but when coexpressed with GluR5-7 receptor subunits, they form channels with high affinity for kainate. Like AMPA receptors, the functional unit of endogenous kainate receptors is believed to be a tetramer, which can be either homomeric or heteromeric. Kainate receptors GluR5 and GluR6 (but not GluR7, KA-1, or KA-2) can undergo RNA editing; as in the AMPA receptor GluR2, a glutamine (Q) residue in the channel pore is edited to encode arginine (R) in the mature protein. Substitution of Q with R modulates the properties of the channel, producing channels with reduced single channel conductance and lower permeability to Ca²⁺.