Gα16 interacts with tetratricopeptide repeat 1 (TPR1) through its β3 region to activate Ras independently of phospholipase Cβ signaling

Abstract

Background: G protein-coupled receptors constitute the largest family of cell surface receptors in the mammalian genome. As the core of the G protein signal transduction machinery, the G subunits are required to interact with multiple partners. The GTP-bound active state of many G subunits can bind a multitude of effectors and regulatory proteins. Yet it remains unclear if the different proteins utilize distinct or common structural motifs on the G subunit for binding. Using G16 as a model, we asked if its recently discovered adaptor protein tetratricopeptide repeat 1 (TPR1) binds to the same region as its canonical effector, phospholipase C (PLC). Results: We have examined the specificity of G16/TPR1 association by testing a series of chimeras between G16 and Gz. TPR1 co-immunoprecipitated with G16 and more tightly with its constitutively active G 16 QL, but not Gz. Progressive replacement of G 16 sequence with the corresponding residues of Gz eventually identified a stretch of six amino acids in the 3 region of G 16 which are responsible for TPR1 interaction and the subsequent Ras activation. Insertion of these six residues into Gz allowed productive TPR1-interaction. Since the 3 region only minimally contributes to interact with PLC, several chimeras exhibited differential abilities to stimulate PLC and Ras. The ability of the chimeras to activate downstream transcription factors such as signal transducer and activator of transcription 3 and nuclear factor B appeared to be associated with PLC signaling. Conclusions: Our results suggest that G16 can signal through TPR1/Ras and PLC simultaneously and independently. The 3 region of G16 is essential for interaction with TPR1 and the subsequent activation of Ras, but has relatively minor influence on the PLC interaction. G16 may utilize different structural domains to bind TPR1 and PLC. © 2011 Liu et al; licensee BioMed Central Ltd.