Assembly of τ protein into Alzheimer paired helical filaments depends on a local sequence motif ( ³⁰⁶ VQIVYK ³¹¹ ) forming β structure

Abstract

We have searched for a minimal interaction motif in protein that supports the aggregation into Alzheimer-like paired helical filaments. Digestion of the repeat domain with different proteases yields a GluC-induced fragment comprising 43 residues (termed PHF43), which represents the third repeat of plus some flanking residues. This fragment self assembles readily into thin filaments without a paired helical appearance, but these filaments are highly competent to nucleate bona fide PHFs from full-length . Probing the interactions of PHF43 with overlapping peptides derived from the full sequence yields a minimal hexapeptide interaction motif of 306 VQIVYK 311 at the beginning of the third internal repeat. This motif coincides with the highest predicted ␤-structure potential in . CD and Fourier transform infrared spectroscopy shows that PHF43 acquires pronounced ␤ structure in conditions of self assembly. Point mutations in the hexapeptide region by prolinescanning mutagenesis prevent the aggregation. The data indicate that PHF assembly is initiated by a short fragment containing the minimal interaction motif forming a local ␤ structure embedded in a largely random-coil protein.

Tau Paired Helical Filaments from Alzheimer's Disease Brain and Assembled in Vitro Are Based on β-Structure in the Core Domain

“…This is in agreement with the hydrophilic character of the sequence and tau's high solubility (7), and is evidenced by a negative maximum around 200 nm in the CD spectrum, a peak at ∼1645 cm -1 in the amide I band of the FTIR spectrum, the absence of a defined radius of gyration by X-ray scattering (8,15,23,24), and unusually large Stokes radii [see Results (Figure 5)]. NMR studies of selected tau peptides confirm the absence of ordered secondary structure (except when R-helix is enforced by adding the R-helix inducer trifluoroethanol) (9)(10)(11)(12).…”

“…The data underscore the observations that the repeat domain forms the core of the PHFs (21,22), that the aggregation involves the generation of -structure (23,24), and that the N-and C-terminal flanking domains remain largely as an unstructured "fuzzy coat".…”

Tau protein liquid–liquid phase separation can initiate tau aggregation

“…The in vitro aggregation of tau into amyloid‐like fibrils has been manifold described by several authors, mostly with emphasis on aggregation kinetics and aggregate structure (von Bergen et al , 2000; Tepper et al , 2014). Most of these aggregation studies have been performed on non‐phosphorylated recombinant tau (tau441), which needs the addition of polyanionic co‐factors such as heparin (Goedert et al , 1996) or RNA (Kampers et al , 1996) in order to form aggregates.…”

Tau-Based Treatment Strategies in Neurodegenerative Diseases

“…140,141 On the contrary, phosphorylation of the KXGS motifs in the repeat region inhibits tau aggregation in vitro. 86 Tau comprises two hydrophobic hexapeptide motifs 144,145 in the repeat domains (275VQIINK280 at the beginning of R2 and 306VQIVYK311 at the beginning of R3) that form a cross ␤-structure and make up the PHF core. The N-and C-terminal flanking regions are thought to form the PHF fuzzy coat.…”

“…146 Proteolytic cleavage of the inhibitory N-and C-termini exposes the aggregation-prone hexapeptide motifs, thereby greatly facilitating the nucleation of filaments. 144,147 There has been debate on what form of tau is the toxic species for neurons. Elevation of tau, phosphorylation of tau at different sites, and truncation by different proteases have been investigated.…”