Casein kinase II preferentially phosphorylates human tau isoforms containing an amino-terminal insert. Identification of threonine 39 as the primary phosphate acceptor

J. A. Greenwood, C. W. Scott, R. C. Spreen, C. B. Caputo, G. V.W. Johnson

Research output: Contribution to journalArticle

75 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)4373-4380
Number of pages8
JournalJournal of Biological Chemistry
Volume269
Issue number6
StatePublished - 1994

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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