Protein Anatomy:  C-Tail Region of Human Tau Protein as a Crucial Structural Element in Alzheimer's Paired Helical Filament Formation in Vitro

Abstract

Tau is a microtubule-associated protein in mammalian brain. In Alzheimer's disease, this protein is present in the somatodendritic compartment of certain nerve cells, where it forms a portion of paired helical filament, the major constituent of the neurofibrillary tangle. For clarification of the mechanism of this formation, recombinant human tau and its fragments (N-terminal half, C-terminal half, and 4-repeats) expressed in Escherichia coli were prepared, eight peptide fragments (C-tails 1-8) of the C-tail region were synthesized, and the conformation and capacity for aggregation essential for filamentous structure formation in vitro were examined. Recombinant full-length tau, the N-terminal half, 4-repeats, and the C-terminal half did not form filamentous structures in aqueous solution after standing at 20 degrees C. Peptides corresponding to the C-tail region of tau, C-tail 5, C-tail 7, and C-tail 8, produced the paired filament or single straight filament in acidic solution. The rate of filament formation by each peptide was followed by circular dichroism, which showed the C-tails to have predominantly random coil structures immediately following dissolution in aqueous solution and be gradually converted to the beta-sheet structure. The kinetics of aggregation were characterized by a delay period during which the solution remained clear, followed by a nucleation event which led to a growth phase, whose negative peak intensity at 218 nm in circular dichroism increased due to filamentous structure formation. This delay was eliminated by seeding supersaturated solution of preformed filaments. C-tails interacted with recombinant full-length tau to form definite single straight filament. The C-tail region of tau is thus shown indispensable to the formation of paired helical filament and nucleation to reduce the rate of paired helical filament formation in amyloidogenesis in vitro. These findings may provide some clarification of the pathogenesis of Alzheimer's disease.

Proapoptotic Effects of Tau Cleavage Product Generated by Caspase-3

“…The C-terminus including the microtubule-binding domains and region spanning 351-380 residues of Tau appears to contribute to microtubule organization (Lee et al, 1989;Brandt and Lee, 1993) and to PHF core formation in vitro, respectively (Kondo et al, 1988;Yanagawa et al, 1998). We used an anti-PHF-1 Ab that recognizes the phosphorylated, PHF-like C-terminal of Tau (residues 387-404) in Alzheimer's patients (Otvos et al, 1994), to show that Tau is susceptible to cleavage by caspase during the process of neuronal cell death.…”

Phosphorylation Regulates Tau Interactions with Src Homology 3 Domains of Phosphatidylinositol 3-Kinase, Phospholipase Cγ1, Grb2, and Src Family Kinases

“…Tau-Glu10 had glutamates at positions 198,199,202,231,235,396,404,409,413, and 422 (34) (numbering of the tau sequence is based on the 2N4R isoform of human tau, containing 441 amino acids (32)). Tau constructs for expressing the N-terminal (1-249) and C-terminal (250 -441) halves of tau (Tau-NT and Tau-CT containing, respectively, residues 1-249 and 250 -441 of 0N4R tau) were donated by Dr. H. Yanagawa (Keio University, Yokohama, Japan) (35). The various constructs used are illustrated diagrammatically in Fig.…”

The Formation of Straight and Twisted Filaments from Short Tau Peptides

“…These structures are frequently seen before the appearance of fibers, and it has been proposed that they are intermediates in amyloid formation (79). If it is assumed that the smallest nucleation site is a peptide of the general structure (X) n K (or K(X) n ), where n Ն 2 and X is a residue frequently found in ␤-sheet, then there are several potential nucleation sites in tau that satisfy this criteria including 87 (30,80). If the criteria for a potential nucleus is broadened to include the general structure (X) n Z (or Z(X) n ), where Z is a charged residue and X is a residue frequently found in ␤-sheet, then the number of potential nuclei for amyloid formation in tau becomes much larger.…”