title: Casein kinase II preferentially phosphorylates human tau isoforms containing an amino-terminal insert. Identification of threonine 39 as the primary phosphate acceptor.
abstract: The in vitro phosphorylation of the microtubule-associated protein tau by casein kinase II was studied. Purified human brain tau was phosphorylated by casein kinase II to a stoichiometry of 0.7 mol of 32P/mol of tau. Individual recombinant human tau isoforms were phosphorylated to stoichiometries ranging from 0.2 to 0.8 mol of 32P/mol of tau. Casein kinase II catalyzed a 4-fold greater incorporation of phosphate into the tau isoform containing a 58-amino acid insert near its amino terminus (T4L) than the isoforms without the 58-amino acid insert (T3 and T4). Phosphopeptide mapping of casein kinase II phosphorylated human tau and recombinant tau isoforms suggested that the isoforms containing an amino-terminal insert constitute the major substrates for casein kinase II within the tau family. The sites of phosphorylation on T4L were identified by digesting phosphorylated T4L with the protease Asp-N, separating the peptides by reversed phase high performance liquid chromatography, and analyzing the isolated peptides by liquid-secondary ion mass spectrometry and solid-phase amino-terminal sequencing. Thr39 was identified as the predominant phosphorylation site, which is located 5 residues from the amino-terminal insert in T4L. Phosphopeptide mapping of tau isolated from LA-N-5 neuroblastoma cells indicates that Thr39 is phosphorylated in situ. To our knowledge, this is the first demonstration of a differential phosphorylation of the human tau isoforms, with the isoforms containing the acidic amino-terminal insert being the preferred substrates of casein kinase II.
authors.affiliation: Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham 35294.
authors.forename: J A
authors.initials: JA
authors.lastname: Greenwood
authors.forename: C W
authors.initials: CW
authors.lastname: Scott
authors.forename: R C
authors.initials: RC
authors.lastname: Spreen
authors.forename: C B
authors.initials: CB
authors.lastname: Caputo
authors.forename: G V
authors.initials: GV
authors.lastname: Johnson
mesh_terms: D000595:Amino Acid Sequence; D047390:Casein Kinase II; D006801:Humans; D066298:In Vitro Techniques; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010449:Peptide Mapping; D010769:Phosphothreonine / Q000378:metabolism; D011094:Polyethyleneimine / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D016875:tau Proteins / Q000145:classification / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D016875:tau Proteins; D010769:Phosphothreonine; D011094:Polyethyleneimine; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases