4.6 Article

Reversible phosphorylation of the signal transduction complex in Drosophila photoreceptors

Journal

JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 275, Issue 16, Pages 12194-12199

Publisher

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.275.16.12194

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In the Drosophila visual cascade, the transient receptor potential (TRP) calcium channel, phospholipase C beta (no-receptor-potential A), and an eye-specific isoform of protein kinase C (eye-PKC) comprise a multimolecular signaling complex via their interaction with the scaffold protein INAD, Previously, we showed that the interaction between INAD and eye-PKC is a prerequisite for deactivation of a light response, suggesting eye-PKC phosphorylates proteins in the complex. To identify substrates of eye-PKC, we immunoprecipitated the complex from head lysates using anti-INAD antibodies and performed in vitro kinase assays. Wild-type immunocomplexes incubated with [P-32]ATP revealed phosphorylation of TRP and INAD. In contrast, immunocomplexes from inaC mutants missing eye-PKC, displayed no phosphorylation of TRP or INAD. We also investigated protein phosphatases that may be involved in the dephosphorylation of proteins in the complex, Dephosphorylation of TRP and INAD was partially suppressed by the protein phosphatase inhibitors okadaic acid, microcystin, and protein phosphatase inhibitor-2, These phosphatase activities were enriched in the cytosol of mild-type heads, but drastically reduced in extracts prepared from glass mutants, which lack photoreceptors, Our findings indicate that INAD functions as RAGE (receptor for activated PKC), allowing eye-PKC to phosphorylate INAD and TRP. Furthermore, dephosphorylation of INAD and TRP is catalyzed by PP1/PP2A-like enzymes preferentially expressed in photoreceptor cells.

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