MUTAGENESIS OF THE GABA RHO-1 RECEPTOR ALTERS AGONIST AFFINITY AND CHANNEL GATING

SEVENTEEN site-directed mutations were constructed in the GABA rho 1 r eceptor with the aim of finding agonist binding domains common to rho 1 and rho 2 receptors but distinct from those identified in members of the family of homologous, ligand gated ion channels. Mutated cDNAs we re expressed in Xenopus oocytes and tested by voltage clamp experiment s. Five of the mutations abolished responsiveness to GABA. Mutation Q1 89H, in the conserved cystein loop, diminished apparent GABA affinity to about 1/10 of wild type values in a manner consistent with decrease d allosteric cooperativity among agonist recognition sites. Mutation R 316A, located in the extracellular loop between transmembrane domains II and III, increased the Hill coefficient to 3.9 in a fashion consist ent with enhanced open probability of a receptor multimer.