Interaction of different third intracellular loop fragments of human dopamine d2l receptor with a-subunit of gi1 protein - prospective therapeutic application

Summary: In order to find the essential structural motif of the D2L dopamine receptor necessary for the interaction with a-subunit of Gi1 protein, four fragments of the third cytoplasmic loop (CPL3) of this receptor were cloned, expressed in E. coli and purified. After that, fusion proteins with glutathione-S-transferase (GST) were prepared and the interactions quantified by a colorimetric assay for GST activity determination. The presence of D2L-CPL3 fragment-Gia1 complexes was detected by SDS-polyacrylamide gel electrophoresis (PAGE). Kd values for the interaction of the three fragments with Gia1 were similar and in nmol/L range of concentrations, while the peptide representing the insert in the long form of the dopamine D2 receptor expressed about 10-fold lower binding affinity. These results could serve to design new therapeutic agents that might act at the level of receptor/G protein interaction rather than at the level of ligand-receptor binding.