Association of INAD with NORPA is Essential for Controlled Activation and Deactivation of Drosophila Phototransduction in vivo

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 94; no. 23; pp. 12682 - 12687
• Main Authors: Shieh, Bih-Hwa, Zhu, Mei-Ying, Lee, John K., Kelly, Ingrid M., Bahiraei, Frohar
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 11-11-1997; National Acad Sciences; The National Academy of Sciences of the USA
• Subjects: Animals; Animals, Genetically Modified; Antibodies; Biological Sciences; Calcium; Calcium channels; Drosophila; Drosophila - physiology; Drosophila Proteins; Eye Proteins - physiology; Kinetics; Neurons; Phenotypes; Phosphatidylinositol Diacylglycerol-Lyase; Phospholipase C beta; Proteins; Signal Transduction; TRPC cation channels; Type C Phospholipases - physiology; Vision, Ocular - physiology; Visual perception
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.23.12682

Visual transduction in Drosophila is a G protein-coupled phospholipase C-mediated process that leads to depolarization via activation of the transient receptor potential (TRP) calcium channel. Inactivation-no-afterpotential D (INAD) is an adaptor protein containing PDZ domains known to interact with TRP. Immunoprecipitation studies indicate that INAD also binds to eye-specific protein kinase C and the phospholipase C, no-receptor-potential A (NORPA). By overlay assay and site-directed mutagenesis we have defined the essential elements of the NORPA-INAD association and identified three critical residues in the C-terminal tail of NORPA that are required for the interaction. These residues, Phe-Cys-Ala, constitute a novel binding motif distinct from the sequences recognized by the PDZ domain in INAD. To evaluate the functional significance of the INAD-NORPA association in vivo, we generated transgenic flies expressing a modified NORPA, NORPAC1094S, that lacks the INAD interaction. The transgenic animals display a unique electroretinogram phenotype characterized by slow activation and prolonged deactivation. Double mutant analysis suggests a possible inaccessibility of eye-specific protein kinase C to NORPAC1094S, undermining the observed defective deactivation, and that delayed activation may similarly result from NORPAC1094Sbeing unable to localize in close proximity to the TRP channel. We conclude that INAD acts as a scaffold protein that facilitates NORPA-TRP interactions required for gating of the TRP channel in photoreceptor cells.