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G Hu, TG Wensel; R9AP, a membrane anchor for the photoreceptor GAP, RGS9-1 . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2897.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the regulation and membrane interaction of the photoreceptor GAP (GTPase Accelerating Protein), RGS9-1. Methods: RGS9-1 was immunoprecipitated from detergent-solubilized ROS membranes. A novel 25 kDa protein that co-immunoprecipitated was identified by internal peptide sequencing and library screening. The expression and localization of the 25 kD protein (R9AP, RGS9-1 Anchor Protein) was examined by multiple tissue northern blot, western blot on sucrose gradient fractionated retinal membranes, and immunostaining of eye-cup sections. The membrane binding properties of R9AP were examined by extracting ROS membranes with different buffers. Results: Detergent extracts contain a stoichiometric complex of RGS9-1, Gß5L, Gαt, and a novel 25 kDa phosphorylated protein, R9AP. R9AP is encoded by one intronless gene, with no close homologues in the human; and the same is true for the mouse genome. Full or partial cDNA or genomic clones were obtained from mice, cattle, human, zebrafish and Xenopus laevis. Its expression is almost entirely confined to the retina and is mainly observed in photoreceptor outer segments. R9AP contains a single membrane-spanning helix near its carboxyl terminus and behaves as a transmembrane protein in ROS membranes. Conclusion: RGS9-1 is tethered to the ROS membranes by R9AP, with help from fatty acylated Gαt. R9AP may also play other roles in phototransduction.
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