An intact helical domain is required for Gα 14 to stimulate phospholipase Cβ

Background Stimulation of phospholipase Cβ (PLCβ) by the activated α-subunit of G q (Gα q ) constitutes a major signaling pathway for cellular regulation, and structural studies have recently revealed the molecular interactions between PLCβ and Gα q . Yet, most of the PLCβ-interacting residues identified on Gα q are not unique to members of the Gα q family. Molecular modeling predicts that the core PLCβ-interacting residues located on the switch regions of Gα q are similarly positioned in Gα z which does not stimulate PLCβ. Using wild-type and constitutively active chimeras constructed between Gα z and Gα 14 , a member of the Gα q family, we examined if the PLCβ-interacting residues identified in Gα q are indeed essential. Results Four chimeras with the core PLCβ-interacting residues composed of Gα z sequences were capable of binding PLCβ2 and stimulating the formation of inositol trisphosphate. Surprisingly, all chimeras with a Gα z N-terminal half failed to functionally associate with PLCβ2, despite the fact that many of them contained the core PLCβ-interacting residues from Gα 14 . Further analyses revealed that the non-PLCβ2 interacting chimeras were capable of interacting with other effector molecules such as adenylyl cyclase and tetratricopeptide repeat 1, indicating that they could adopt a GTP-bound active conformation. Conclusion Collectively, our study suggests that the previously identified PLCβ-interacting residues are insufficient to ensure productive interaction of Gα 14 with PLCβ, while an intact N-terminal half of Gα 14 is apparently required for PLCβ interaction.