A68 proteins in Alzheimer's disease are composed of several tau isoforms in a phosphorylated state which affects their electrophoretic mobilities

• Published in: Biochemical journal Vol. 279; no. 3; pp. 831 - 836
• Main Authors: BRION, J.-P, HANGER, D. P, COUCK, A.-M, ANDERTON, B. H
• Format: Journal Article
• Language: English
• Published: Colchester Portland Press 01.11.1991
• Subjects: Aged; Aged, 80 and over; Alzheimer Disease - metabolism; Alzheimer Disease - pathology; Amino Acid Sequence; Biological and medical sciences; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Electrophoresis, Polyacrylamide Gel; Humans; Medical sciences; Microscopy, Immunoelectron; Middle Aged; Molecular Sequence Data; Nerve Tissue Proteins - chemistry; Nerve Tissue Proteins - isolation & purification; Nerve Tissue Proteins - ultrastructure; Neurology; Phosphorylation; Stereoisomerism; tau protein; tau Proteins - chemistry; tau Proteins - isolation & purification; tau Proteins - ultrastructure; Human; Nervous system diseases; Molecular form; Antibody; Alzheimer disease; Paired helical filament; Immunocytochemistry; Electrophoretic mobility; Immunoblotting assay; Degenerative disease; Comparative study; Aminoacid sequence; Brain (vertebrata)
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj2790831

The tau-immunoreactive A68 polypeptides found in brains from patients with Alzheimer's disease have been studied by Western blotting using (1) antibodies to synthetic peptides corresponding to sequences that span the complete human tau molecule, and (2) antibodies specific for inserts 1 and 2 found towards the N-terminus of some tau isoforms. The three major A68 polypeptides were labelled by all of the antibodies to sequences common to all tau isoforms, but the faster-migrating A68 polypeptides was not labelled by either of the two antibodies specific for inserts 1 and 2. Treatment with alkaline phosphatase of non-solubilized A68 did not change its electrophoretic mobility on SDS/PAGE under the conditions described here. However, A68 that was solubilized before treating it with alkaline phosphatase was found to move faster on SDS/PAGE than untreated A68, to a position similar to that of normal tau. We also confirmed that A68 preparations contain numerous paired helical filaments (PHF). These PHF were labelled by all anti-tau antibodies, including insert-specific antibodies. Our results further support the notion that PHF contain abnormally phosphorylated tau in an aggregated state, and indicate that these abnormally phosphorylated tau forms are composed of several tau isoforms and that the full length of the tau molecule is present in these polypeptides.