title: Structural and functional implications of tau hyperphosphorylation: information from phosphorylation-mimicking mutated tau proteins.
abstract: Abnormal tau-immunoreactive filaments are a hallmark of tauopathies, including Alzheimer's disease (AD). A higher phosphorylation ("hyperphosphorylation") state of tau protein may represent a critical event. To determine the potential role of tau hyperphosphorylation in these disorders, mutated tau proteins were produced where serine/threonine residues known to be highly phosphorylated in tau filaments isolated from AD patients were substituted for glutamate to simulate a paired helical filament (PHF)-like tau hyperphosphorylation. We demonstrate that, like hyperphosphorylation, glutamate substitutions induce compact structure elements and SDS-resistant conformational domains in tau protein. Hyperphosphorylation-mimicking glutamate-mutated tau proteins display a complete functional loss in its ability to promote microtubule nucleation which can partially be overcome by addition of the osmolyte trimethylamine N-oxide (TMAO), which is similar to phosphorylated tau. In addition, glutamate-mutated tau proteins fail to interact with the dominant brain protein phosphatase 2A isoform ABalphaC, and exhibit a reduced ability to assemble into filaments. Interestingly, wild-type tau and phosphorylation-mimicking tau similarly bind to microtubules when added alone, but the mutated tau is almost completely displaced from the microtubule surface by equimolar concentrations of wild-type tau. The data indicate that glutamate-mutated tau proteins provide a useful model for analyzing the functional consequences of tau hyperphosphorylation. They suggest that several mechanisms contribute to the abnormal tau accumulation observed during tauopathies, in particular a selective displacement of hyperphosphorylated tau from microtubules, a functional loss in promoting microtubule nucleation, and a failure to interact with phosphatases.
authors.affiliation: Department of Neurobiology, IZN, University of Heidelberg, INF 345, 69120 Heidelberg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Eidenmüller
authors.forename: T
authors.initials: T
authors.lastname: Fath
authors.forename: A
authors.initials: A
authors.lastname: Hellwig
authors.forename: J
authors.initials: J
authors.lastname: Reed
authors.forename: E
authors.initials: E
authors.lastname: Sontag
authors.forename: R
authors.initials: R
authors.lastname: Brandt
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000328:Adult; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D018698:Glutamic Acid / Q000235:genetics; D006801:Humans; D008870:Microtubules / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018716:Molecular Mimicry / Q000235:genetics*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D054648:Protein Phosphatase 2; D012694:Serine / Q000235:genetics; D013329:Structure-Activity Relationship; D013912:Threonine / Q000235:genetics; D016875:tau Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology
chemical_list: D016875:tau Proteins; D013912:Threonine; D018698:Glutamic Acid; D012694:Serine; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2