Palmitoylation but not the extreme amino‐terminus of Gqα is required for coupling to the NK2 receptor

Abstract

G_qα and G_11α differ from other G protein α subunits in that they have unique, conserved 6 residue amino‐terminal extensions. Wild‐type and amino‐terminal mutants of G_qα expressed in COS cells were analyzed for their ability to functionally couple with co‐expressed neurokinin NK2 receptor. Wild‐type, T2A and Δ2–7 G_qα were able to stimulate agonist driven phospholipase C (PLC) activity in identical manners. Other activities of these two amino‐terminal mutants including aluminum fluoride stimulated PLC activity, palmitoylation, interaction with G_βγ subunits and GTPγS‐induced trypsin resistance are also similar to the wild‐type α subunit. This demonstrates that the NK2 receptor is able to functionally interact with the α subunit of G_q and that the first seven amino‐acids of G_qα are not required for any of the α subunit functions tested. In contrast to the T2A and Δ2–7 mutants, a C9,10A G_qα mutant was not able to couple to either the NK2 receptor or PLC, as assessed by high‐affinity agonist binding and activation of PLC either in intact cells or in vitro. The C9,10A protein was able to assume a GTPγS‐induced trypsin‐resistant conformation and partitioned primarily to the pelletable fraction in a manner similar to the wild‐type protein. However, it was not labeled with [³H]palmitic acid. This suggests that blocking palmitoylation at the amino‐terminus of G_qα results in a loss of functional activity which reflects an inability to interact with both the receptor and downstream signaling targets.