Interaction of guanine nucleotides with the kainate binding protein from chick cerebellum

The interaction of guanine nucleotides with the chick cerebellar kainate binding protein (chKBP) was studied using binding assays, immunoblotting, and in vitro phosphorylation experiments. Guanosine 5'-triphosphate (GTP) was found to reduce [3H]kainic acid (KA) binding in a concentration-dependent manner. Similarly, an inhibition of [3H]GTP binding by KA was observed. No G protein co-purified with chKBP. chKBP phosphorylation by the cAMP-dependent protein kinase (PKA) was prevented both by KA and by GTP. Neither KA nor GTP blocked each other's effect in chKBP phosphorylation. The present findings suggest that chKBP harbours two agonistic binding sites, one in the micromolar range, detected by binding techniques and one in the millimolar range detected by phosphorylation assays. Guanine nucleotides interact with both sites.