The visual G protein of fly photoreceptors interacts with the PDZ domain assembled INAD signaling complex via direct binding of activated Gαq to phospholipase Cβ

Visual transduction in the compound eye of flies is a well-established model system for the study of G protein-coupled transduction pathways. Pivotal components of this signaling pathway, including the principal light-activated Ca2+ channel transient receptor potential, an eye specific protein kinase C, and the norpA-encoded phospholipase C beta, are assembled into a supramolecular signaling complex by the modular PDZ domain protein INAD. We have used immunoprecipitation assays to study the interaction of the heterotrimeric visual G protein with this INAD signaling complex, Light-activated G alpha(q)- guanosine 5'-O-(thiotriphosphate) and Alf(4)(-)-activated G alpha(q), but not G beta gamma, form a stable complex with the INAD signaling complex. This interaction requires the presence of norpA-encoded phospholipase C beta, indicating that phospholipase C beta is the target of activated G alpha(q). Our data establish that the INAD signaling complex is a light-activated target of the phototransduction pathway, with G alpha(q), forming a molecular on-off switch that shuttles the visual signal from activated rhodopsin to INAD-linked phospholipase C beta.