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In sporadic Alzheimer's disease (AD), neurofibrillary lesion formation is preceded by extensive post-translational modification of the microtubule associated protein tau. To identify the modification signature associated with tau lesion formation at single amino acid resolution, immunopurified paired helical filaments were isolated from AD brain and subjected to nanoflow liquid chromatography-tandem mass spectrometry analysis. The resulting spectra identified monomethylation of lysine residues as a new tau modification. The methyl-lysine was distributed among seven residues located in the projection and microtubule binding repeat regions of tau protein, with one site, K254, being a substrate for a competing lysine modification, ubiquitylation. To characterize methyl lysine content in intact tissue, hippocampal sections prepared from post mortem late-stage AD cases were subjected to double-label confocal fluorescence microscopy using anti-tau and anti-methyl lysine antibodies. Anti-methyl lysine immunoreactivity colocalized with 78 ± 13% of neurofibrillary tangles in these specimens. Together these data provide the first evidence that tau in neurofibrillary lesions is post-translationally modified by lysine methylation.
Greenebaum Cancer Center, University of Maryland, Baltimore, MD, 21201, USA.
This article was published in the following journal.
Name: Acta neuropathologica
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The specific patterns of POST-TRANSLATIONAL PROTEIN MODIFICATION of HISTONES, i.e. histone ACETYLATION; METHYLATION; PHOSPHORYLATION; and ubiquitination, at specific amino acid residues, that are involved in assembly, maintenance, and modification of different chromatin structural states, such as EUCHROMATIN and HETEROCHROMATIN.
A histone-lysine N-methyltransferase and catalytic subunit of Polycomb Repressive Complex 2. It methylates LYSINE 9 (H3K9me) and LYSINE 27 (H3K27me) of HISTONE H3, leading to transcriptional repression of the affected target gene. EZH2 also methylates non-histone proteins such as GATA4 TRANSCRIPTION FACTOR and the nuclear receptor RORA. It regulates CIRCADIAN CLOCKS via histone methylation at the PROMOTER REGIONS of the circadian genes and its repressive activity is also important for the identity and differentiation of EMBRYONIC STEM CELLS.
An enzyme that catalyzes the methylation of the epsilon-amino group of lysine residues in proteins to yield epsilon mono-, di-, and trimethyllysine. EC 18.104.22.168.
A precursor to the AMYLOID BETA-PROTEIN (beta/A4). Alterations in the expression of the amyloid beta-protein precursor (ABPP) gene, located on chromosome 21, plays a role in the development of the neuropathology common to both ALZHEIMER DISEASE and DOWN SYNDROME. ABPP is associated with the extensive extracellular matrix secreted by neuronal cells. Upon cleavage, this precursor produces three proteins of varying amino acid lengths: 695, 751, and 770. The beta/A4 (695 amino acids) or beta-amyloid protein is the principal component of the extracellular amyloid in senile plaques found in ALZHEIMER DISEASE; DOWN SYNDROME and, to a limited extent, in normal aging.
Enzymes that are part of the restriction-modification systems. They are responsible for producing a species-characteristic methylation pattern, on either adenine or cytosine residues, in a specific short base sequence in the host cell's own DNA. This methylated sequence will occur many times in the host-cell DNA and remain intact for the lifetime of the cell. Any DNA from another species which gains entry into a living cell and lacks the characteristic methylation pattern will be recognized by the restriction endonucleases of similar specificity and destroyed by cleavage. Most have been studied in bacterial systems, but a few have been found in eukaryotic organisms.
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