Requirement for the PDZ domain protein, INAD, for localization of the TRP store-operated channel to a signaling complex

In Drosophila, the store-operated Ca²⁺ channel, TRP, is required in photoreceptor cells for a sustained response to light. Here, we show that TRP forms a complex with phospholipase C-β (NORPA), rhodopsin (RH1), calmodulin, and the PDZ domain containing protein INAD. Proteins with PDZ domains have previously been shown to cluster ion channels in vitro. We show that in InaD mutant flies, TRP is no longer spatially restricted to its normal subcellular compartment, the rhabdomere. These results provide evidence that a PDZ domain protein is required, in vivo, for anchoring of an ion channel to a signaling complex. Furthermore, disruption of this interaction results in retinal degeneration. We propose that the TRP channel is linked to NORPA and RH1 to facilitate feedback regulation of these upstream signaling molecules.