IDENTIFICATION OF THE AMINO-ACID SUBSETS ACCOUNTING FOR THE LIGAND-BINDING SPECIFICITY OF A GLUTAMATE-RECEPTOR

In a situation so far unique among neurotransmitter receptors, glutama te receptors share amino acid sequence similarities with the bacterial periplasmic binding proteins (PBPs). On the basis of the primary stru cture similarity of two bacterial periplasmic proteins (lysine/arginin e/ornithine- and phosphate-binding proteins) with the chick cerebellar kainate-binding protein (KBP), a member of the ionotropic glutamate r eceptor family, we have generated a three-dimensional model structure of the KBP extracellular domain. By an interplay between homology mode ling and site-directed mutagenesis, we have investigated the kainate b inding properties of 55 different mutants (corresponding to 43 positio ns) and studied the interactions of some of these mutants with various glutamatergic ligands. As a result, we present here the subsets of am ino acids accounting for the binding free energies and specificities o f KBP for kainate, glutamate, and CNQX and propose a three-dimensional model, at the microarchitectural level, of the glutamatergic binding domain.