title: Characterization of myotubularin-related protein 7 and its binding partner, myotubularin-related protein 9.
abstract: Myotubularin-related protein 7 (MTMR7) is a member of the myotubularin (MTM) family. The cDNA encoding the mouse MTMR7 contains 1,983 bp, and the predicted protein has a deduced molecular mass of 75.6 kDa. Northern and Western blot analyses showed that MTMR7 is expressed mainly in brain and mouse neuroblastoma N1E-115 cells. Recombinant MTMR7 dephosphorylated the D-3 position of phosphatidylinositol 3-phosphate and inositol 1,3-bisphosphate [Ins(1,3)P2]. The substrate specificity of MTMR7 is different than other MTM proteins in that this enzyme prefers the water-soluble substrate. Immunofluorescence showed that MTMR7 is localized in Golgi-like granules and cytosol, and subcellular fractionation showed both cytoplasmic and membrane localization of MTMR7 in N1E-115 cells. An MTMR7-binding protein was found in an anti-MTMR7 immunoprecipitate from N1E-115 cells and identified as MTM-related protein 9 (MTMR9) by tandem mass spectrometry. The coiled-coil domain of MTMR9 was sufficient for binding to MTMR7. The binding of MTMR9 increased the Ins(1,3)P2 phosphatase activity of MTMR7. Our results show that MTMR7 forms a complex with MTMR9 and dephosphorylates phosphatidylinositol 3-phosphate and Ins(1,3)P2 in neuronal cells.
authors.affiliation: Washington University School of Medicine, Department of Internal Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Mochizuki
authors.forename: Philip W
authors.initials: PW
authors.lastname: Majerus
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000201:enzymology; D019556:COS Cells; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017027:Protein Tyrosine Phosphatases / Q000235:genetics* / Q000378:metabolism*; D054558:Protein Tyrosine Phosphatases, Non-Receptor; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D014018:Tissue Distribution
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D007295:Inositol Phosphates; D018129:Phosphatidylinositol Phosphates; D011994:Recombinant Proteins; C055525:phosphatidylinositol 3-phosphate; C051853:inositol 1,3-bisphosphate; D010744:Phosphoric Monoester Hydrolases; C478104:Mtmr7 protein, mouse; C478105:Mtmr9 protein, mouse; D017027:Protein Tyrosine Phosphatases; D054558:Protein Tyrosine Phosphatases, Non-Receptor; C099588:myotubularin