Biochemical characterization of mapmodulin, a protein that binds microtubule-associated proteins.
Mapmodulin is a 31-kDa protein that stimulates the microtubule- and dynein-dependent localization of Golgi complexes in semi-intact Chinese hamster ovary cells. We have shown previously that it binds the microtubule binding domains of the microtubule-associated proteins, MAP2, MAP4, and tau. We also showed that mapmodulin is identical to a protein named PHAPI (Vaesen, M., Barnikol-Watanabe, S. , Götz, H., Awni, L.A., Cole, T., Zimmermann, B., Kratzin, H.D. and Hilschmann, N. (1994) Biol. Chem. Hoppe-Seyler 375, 113-126). We report here that mapmodulin is a phosphoprotein that is predominantly cytosolic but is also found peripherally associated with endoplasmic reticulum and Golgi membranes in mammalian cells. The protein occurs as a trimer in cytosol, and phosphorylation is required for its microtubule-associated protein-binding activity. Heat treatment of nonphosphorylated mapmodulin can render it competent for binding to microtubule-associated proteins, suggesting that phosphorylation induces a conformational change in mapmodulin. Finally, despite identity in polypeptide sequence with a protein reported to act as an inhibitor of protein phosphatase 2A, native mapmodulin was not able to inhibit protein phosphatase 2A in Chinese hamster ovary cell cytosol.
Ulitzur
N
N
Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305-5307, USA. pfeffer@cmgm.stanford.edu
Rancaño
C
C
Pfeffer
S R
SR
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002417:Cattle; D002451:Cell Compartmentation; D006224:Cricetinae; D004398:Dyneins / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D019084:Fluorescent Antibody Technique, Indirect; D006056:Golgi Apparatus / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010446:Peptide Fragments / Q000737:chemistry; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D016601:RNA-Binding Proteins; D016415:Sequence Alignment
C087425:ANP32A protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D010446:Peptide Fragments; D010750:Phosphoproteins; D011506:Proteins; D016601:RNA-Binding Proteins; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D004398:Dyneins