title: The G-protein-coupled receptor phosphatase: a protein phosphatase type 2A with a distinct subcellular distribution and substrate specificity.
abstract: Phosphorylation of G-protein-coupled receptors plays an important role in regulating their function. In this study the G-protein-coupled receptor phosphatase (GRP) capable of dephosphorylating G-protein-coupled receptor kinase-phosphorylated receptors is described. The GRP activity of bovine brain is a latent oligomeric form of protein phosphatase type 2A (PP-2A) exclusively associated with the particulate fraction. GRP activity is observed only when assayed in the presence of protamine or when phosphatase-containing fractions are subjected to freeze/thaw treatment under reducing conditions. Consistent with its identification as a member of the PP-2A family, the GRP is potently inhibited by okadaic acid but not by I-2, the specific inhibitor of protein phosphatase type 1. Solubilization of the membrane-associated GRP followed by gel filtration in the absence of detergent yields a 150-kDa peak of latent receptor phosphatase activity. Western blot analysis of this phosphatase reveals a likely subunit composition of AB alpha C. PP-2A of this subunit composition has previously been characterized as a soluble enzyme, yet negligible soluble GRP activity was observed. The subcellular distribution and substrate specificity of the GRP suggests significant differences between it and previously characterized forms of PP-2A.
authors.affiliation: Howard Hughes Medical Research Institute, Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Pitcher
authors.forename: E S
authors.initials: ES
authors.lastname: Payne
authors.forename: C
authors.initials: C
authors.lastname: Csortos
authors.forename: A A
authors.initials: AA
authors.lastname: DePaoli-Roach
authors.forename: R J
authors.initials: RJ
authors.lastname: Lefkowitz
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000201:enzymology; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D002850:Chromatography, Gel; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018411:Spodoptera; D013347:Subcellular Fractions / Q000201:enzymology; D013379:Substrate Specificity
chemical_list: D011956:Receptors, Cell Surface; D020794:Receptor Protein-Tyrosine Kinases; D010749:Phosphoprotein Phosphatases; D019204:GTP-Binding Proteins