title: Molecular aging of tau: disulfide-independent aggregation and non-enzymatic degradation in vitro and in vivo.
abstract: Smearing from high-molecular-mass regions to low-molecular-mass regions on western blot is the most striking observation of the tau making up paired helical filaments in brain tissues affected by Alzheimer's disease. Because our previous study showed site-specific deamidation/isomerization in the smeared tau in vivo, a feature of protein aging, recombinant tau was subjected to prolonged (up to 90 days) in vitro incubation. Carboxymethylated tau at approximately 50 kDa gradually disappeared and was converted to dimers and to high- and low-molecular-mass smearing. In addition, the same site-specific deamidation/isomerization as previously identified in the smeared tau in vivo emerged. Most importantly, tau was spontaneously degraded, generating fragments that start from bulky residues next to asparaginyl residues. This spontaneous degradation of tau probably represents non-enzymatic cleavage through the formation of succinimide intermediates. Similar degradation products starting from the bulky residues next to asparaginyl residues were found in the smeared tau in vivo partially purified from the homogenates from Alzheimer's disease brains.
authors.affiliation: Biomolecular Characterization Division, Characterization Center, RIKEN (The Institute of Physical and Chemical Research), Wako, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Watanabe
authors.forename: Won-Kyoung
authors.initials: WK
authors.lastname: Hong
authors.forename: Naoshi
authors.initials: N
authors.lastname: Dohmae
authors.forename: Koji
authors.initials: K
authors.lastname: Takio
authors.forename: Maho
authors.initials: M
authors.lastname: Morishima-Kawashima
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ihara
mesh_terms: D000375:Aging / Q000378:metabolism*; D000544:Alzheimer Disease / Q000378:metabolism*; D000595:Amino Acid Sequence; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D001923:Brain Chemistry; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004220:Disulfides / Q000378:metabolism*; D004798:Enzymes; D006801:Humans; D066298:In Vitro Techniques; D013058:Mass Spectrometry / Q000379:methods; D008854:Microscopy, Electron / Q000379:methods; D016874:Neurofibrillary Tangles / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D016875:tau Proteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D004220:Disulfides; D004798:Enzymes; D020033:Protein Isoforms; D011994:Recombinant Proteins; D016875:tau Proteins