title: Cross-linking of ubiquitin, HSP27, parkin, and alpha-synuclein by gamma-glutamyl-epsilon-lysine bonds in Alzheimer's neurofibrillary tangles.
abstract: The accumulation of misfolded proteins in intracellular inclusions is a generic feature of neurodegenerative disorders. Although heavily ubiquitylated, the aggregated proteins are not degraded by the proteasomes. A possible reason for this phenomenon may be a modification of deposited proteins by transglutaminases forming gamma-glutamyl-epsilon-lysine (GGEL) cross-links between distinct proteins. Here, we show that the frequency of GGEL cross-links is an order of magnitude higher in Alzheimer's brain cortex than in age-matched or younger controls. This difference is due to the accumulation of GGEL cross-links in ubiquitin-immunopositive protein particles present in both Alzheimer's brains and those from aged individuals. The highly cross-linked protein aggregates show immunoreactivity to antibodies against tau and neurofilament proteins, and partially also to alpha-synuclein, indicating that these structures are inherent in Alzheimer's neurofibrillary tangles and Lewy bodies. Using mass sequence analysis, we identified the same six pairs of peptide sequences cross-linked in both senile and Alzheimer's specimens: Gln31 and Gln190 of HSP27 protein are cross-linked with Lys29 and Lys48 of ubiquitin and HSP27 therefore may cross-link two (poly)ubiquitin chains. One lysine residue of parkin and one of alpha-synuclein were also found to be cross-linked. The data suggest that cross-linking of (poly)ubiquitin moieties via HSP27 may have a role in the stabilization of the intraneuronal protein aggregates by interference with the proteasomal elimination of unfolded proteins.
authors.affiliation: Department of Psychiatry, Hungarian Academy of Sciences, Research Center for Molecular Medicine, University of Debrecen, Debrecen, Hungary. znemes@dote.hu
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Nemes
authors.forename: B
authors.initials: B
authors.lastname: Devreese
authors.forename: P M
authors.initials: PM
authors.lastname: Steinert
authors.forename: J
authors.initials: J
authors.lastname: Van Beeumen
authors.forename: L
authors.initials: L
authors.lastname: Fésüs
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000378:metabolism*; D001923:Brain Chemistry; D002540:Cerebral Cortex / Q000737:chemistry / Q000648:ultrastructure; D002851:Chromatography, High Pressure Liquid; D004151:Dipeptides / Q000032:analysis*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005973:Glutamine / Q000737:chemistry; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000302:isolation & purification; D006624:Hippocampus / Q000737:chemistry / Q000648:ultrastructure; D006801:Humans; D002479:Inclusion Bodies / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D046911:Macromolecular Substances; D008297:Male; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000302:isolation & purification; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000302:isolation & purification; D016874:Neurofibrillary Tangles / Q000737:chemistry*; D016900:Neurofilament Proteins / Q000032:analysis; D058225:Plaque, Amyloid / Q000737:chemistry*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012995:Solubility; D051843:Synucleins; D025801:Ubiquitin / Q000737:chemistry* / Q000302:isolation & purification; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry* / Q000302:isolation & purification; D051844:alpha-Synuclein; D016875:tau Proteins / Q000032:analysis
chemical_list: D004151:Dipeptides; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D046911:Macromolecular Substances; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D016900:Neurofilament Proteins; C497604:SNCA protein, human; D051843:Synucleins; D025801:Ubiquitin; D051844:alpha-Synuclein; D016875:tau Proteins; D005973:Glutamine; C001299:epsilon-(gamma-glutamyl)-lysine; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein; D046988:Proteasome Endopeptidase Complex; D008239:Lysine