Kainate-Binding Protein (KBP) Genes
In the same issue of the journal Nature as the initial report from Heinemann's laboratory (7), two other laboratories reported their successes in isolating cDNA clones of kainate-binding protein genes (KBPs). Wada et al.( 9) isolated a cDNA clone for a KBP purified from frog brain by domoic acid affinity chromotography. When this clone is expressed in COS cells or oocytes, KA-binding activity can be shown but no electrical response to KA is detectable. Antibodies against this M, 48K protein cross-react with a protein of M, 99K in rat brain preparations and recognize this cross-reactive material in the same brain regions as GluR-K1 is found. Similarly, Gregor et al.('") reported the isolation of a cDNA for the complete coding region of a KA-binding protein from chick cerebellum which they found to be exclusively associated with Bergmann glial cells. These KBPs may represent the frog and chick versions of the same protein and may be related to the binding region of the complete receptor-channel complex. However, they appear to be missing the first 350 amino acids of - and have only about 25% amino acid identity with the last half of -the GluR-K1 protein. The physiological significance of these KBPs remains to be determined.
GIuR-A Through GIuR-D
Cloning of glutamate receptor genes continued to progress with the report from Seeburg's laboratory of the isolation of cDNAs GluR-A though GluR-D, obtained with probes based on published sequences("). When these genes were expressed in cultured mammalian cells, electrophysiological responses to activation by L-glutamate, quisqualate, AMPA and KA were detected; these inward currents are not elicited by NMDA and are blocked by the non-NMDA receptor antagonist CNQX. The pharmacological properties of the four cDN A-coded proteins correspond to those previously reported in brain, and the authors proposed that they reprcsent a family of AMPA receptors. These receptors respond to kainate at concentrations in the pM range and are called AMPNkainate or AMPNKA receptors by some authors. The results supported the