Mutational analysis of the mouse 5-HT7 receptor: importance of the third intracellular loop for receptor-G-protein interaction.

The mouse serotonin (5-HT) receptor subtype, 5-HT7, belongs to the family of seven transmembrane G-protein-coupled receptors. To identify the structural basis for the coupling of 5-HT7 receptor to G alpha(s) we constructed a number of receptor mutants in which amino acid residues were either substituted or deleted from the second and third intracellular loops. Wild-type and mutant 5-HT7 receptors were expressed in insect cells using the baculovirus vectors. Two mutant receptor species, 5-HT7(E325G) and 5-HT7(K327S), demonstrated markedly impaired abilities to stimulate adenylyl cyclase. The results suggest the importance of the C-terminal region of the third intracellular loop in receptor-G-protein interaction and that specific charged residues, E325 and K327, may play a critical role in this interaction.