The signals initiated by G-protein-coupled receptors (GPCRs) can be fine-tuned by different proteins that bind to the intracellular parts of the receptor and modulate its activity. In search of proteins that are involved in the regulation of the thromboxane A2 receptor (TXA2R, hereafter referred to as TP), a rhodopsin-like receptor that stimulates phospholipase Cβ activity through activation of the Gαq subunit of hetereotrimeric G proteins, Jean-Luc Parent and colleagues (p. ) now identify a new scaffold protein that is involved in the assembly of a signalling complex downstream of this receptor. The researchers show that the membrane-localised protein WD40 repeat 36 (WDR36) interacts with the C-terminus of the TP β-isoform (TPβ) and enhances the production of inositol phosphates downstream of the receptor. They also find that WDR36 associates with Gαq and that the formation of this complex is promoted by TPβ receptor activation. WDR36 competes with the G-protein coupled receptor kinase 2 for binding to Gαq and enhances the complex formation between the Gαq and PLCβ2. In addition, WDR36 is able to associate directly with PLCβ2. On the basis of these results, the authors conclude that WDR36 acts as a scaffold protein that mediates the assembly of the TPβ receptor, Gαq and PLCβ into an active signalling complex from which downstream signals can be efficiently initiated.
