Coupling of a viral K(+)-channel with a glutamate-binding-domain highlights the modular design of ionotropic glutamate-receptors

Ionotropic glutamate receptors (iGluRs) mediate excitatory neuronal signaling in the mammalian CNS. These receptors are critically involved in diverse physiological processes; including learning and memory formation, as well as neuronal damage associated with neurological diseases. Based on partial sequence and structural similarities, these complex cation-permeable iGluRs are thought to descend from simple bacterial proteins emerging from a fusion of a substrate binding protein (SBP) and an inverted potassium (K(+))-channel. Here, we fuse the pore module of the viral K(+)-channel Kcv(ATCV-1) to the isolated glutamate-binding domain of the mammalian iGluR subunit GluA1 which is structural homolog to SBPs. The resulting chimera (GluATCV*) is functional and displays the ligand recognition characteristics of GluA1 and the K(+)-selectivity of Kcv(ATCV-1). These results are consistent with a conserved activation mechanism between a glutamate-binding domain and the pore-module of a K(+)-channel and support the expected phylogenetic link between the two protein families.