Alzheimer disease-specific conformation of hyperphosphorylated paired helical filament-Tau is polyubiquitinated through Lys-48, Lys-11, and Lys-6 ubiquitin conjugation

J Biol Chem. 2006 Apr 21;281(16):10825-38. doi: 10.1074/jbc.M512786200. Epub 2006 Jan 27.

Abstract

One of the key pathological hallmarks of Alzheimer disease (AD) is the accumulation of paired helical filaments (PHFs) of hyperphosphorylated microtubule-associated protein Tau. Tandem mass spectrometry was employed to examine PHF-Tau post-translational modifications, in particular protein phosphorylation and ubiquitination, to shed light on their role in the early stages of Alzheimer disease. PHF-Tau from Alzheimer disease brain was affinity-purified by MC1 monoclonal antibody to isolate a soluble fraction of PHF-Tau in a conformation unique to human AD brain. A large number of phosphorylation sites were identified by employing a data-dependent neutral loss algorithm to trigger MS3 scans of phosphopeptides. It was found that soluble PHF-Tau is ubiquitinated at its microtubule-binding domain at residues Lys-254, Lys-311, and Lys-353, suggesting that ubiquitination of PHF-Tau may be an earlier pathological event than previously thought and that ubiquitination could play a regulatory role in modulating the integrity of microtubules during the course of AD. Tandem mass spectrometry data for ubiquitin itself indicate that PHF-Tau is modified by three polyubiquitin linkages, at Lys-6, Lys-11, and Lys-48. Relative quantitative analysis indicates that Lys-48-linked polyubiquitination is the primary form of polyubiquitination with a minor portion of ubiquitin linked at Lys-6 and Lys-11. Because modification by Lys-48-linked polyubiquitin chains is known to serve as the essential means of targeting proteins for degradation by the ubiquitin-proteasome system, and it has been reported that modification at Lys-6 inhibits ubiquitin-dependent protein degradation, a failure of the ubiquitin-proteasome system could play a role in initiating the formation of degradation-resistant PHF tangles.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Algorithms
  • Alzheimer Disease / metabolism*
  • Amino Acid Sequence
  • Chromatography, Liquid
  • Humans
  • Immunoblotting
  • Immunoprecipitation
  • Lysine / chemistry*
  • Mass Spectrometry
  • Molecular Sequence Data
  • Nerve Degeneration / metabolism
  • Neurofibrillary Tangles / metabolism
  • Peptides / chemistry
  • Phosphorylation
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Conformation
  • Protein Structure, Tertiary
  • Sequence Homology, Amino Acid
  • Serine / chemistry
  • Solvents / chemistry
  • Threonine / chemistry
  • Trypsin / chemistry
  • Ubiquitin / chemistry*
  • tau Proteins / chemistry*

Substances

  • Peptides
  • Solvents
  • Ubiquitin
  • tau Proteins
  • Threonine
  • Serine
  • Trypsin
  • Proteasome Endopeptidase Complex
  • Lysine