Regulation of the TRP calcium channel by eye‐PKC in Drosophila

Abstract

The goal of this research study is to investigate the regulation of Drosophila visual signaling by eye-protein kinase C (eye-PKC). Drosophila visual signaling involves a G-protein coupled PLC beta cascade, initiated by light activation of rhodopsin. Rhodopsin, activates a Gq heterotrimeric protein that stimulates PLC beta. PLC beta catalyzes the hydrolysis of PIP2 into IP3 and DAG, resulting in depolarization of the photoreceptor cell via two plasma membrane channels: transient receptor potential (TRP) calcium channel and TRP-like nonselective cation channel. Deactivation of visual signaling is mediated by eye-PKC, which is activated by both DAG and calcium. Eye-PKC, PLC beta and TRP are constitutively attached to a scaffold protein named INAD. The in vivo function of eye-PKC is dependent on its interaction with INAD. Previously, TRP has been shown to be phosphorylated in vitro by eye-PKC. To investigate the regulation of TRP by eye-PKC, first we will map the eye-PKC phosphorylation sites on TRP. By using a combination of pull-down and in vitro kinase assays of various substrates, we have demonstrated phosphorylation of the TRP C-terminal tail by eye-PKC. Using various substrates and site-directed mutagenesis, we determined that TRP is phosphorylated by eye-PKC at serine 982. These results were confirmed by mass spectrometry analysis of both in vitro and in vivo phosphorylated TRP. We are now analyzing the phenotype of transgenic flies expressing a modified TRP (Ser982Ala) by electroretinogram recordings. This study will give us a better understanding of how phosphorylation modulates TRP channel activity. This research was supported by NIH grant EY09743 (to B.-H.S).