Light-Dependent Phosphorylation of the Drosophila Inactivation No Afterpotential D (INAD) Scaffolding Protein at Thr170 and Ser174 by Eye-Specific Protein Kinase C

Drosophila inactivation no afterpotential D (INAD) is a PDZ domain-containing scaffolding protein that tethers components of the phototransduction cascade to form a supramolecular signaling complex. Here, we report the identification of eight INAD phosphorylation sites using a mass spectrometry approach. PDZ1, PDZ2, and PDZ4 each harbor one phosphorylation site, three phosphorylation sites are located in the linker region between PDZ1 and 2, one site is located between PDZ2 and PDZ3, and one site is located in the N-terminal region. Using a phosphospecific antibody, we found that INAD phosphorylated at Thr170/Ser174 was located within the rhabdomeres of the photoreceptor cells, suggesting that INAD becomes phosphorylated in this cellular compartment. INAD phosphorylation at Thr170/Ser174 depends on light, the phototransduction cascade, and on eye-Protein kinase C that is attached to INAD via one of its PDZ domains.