The Formation of Straight and Twisted Filaments from Short Tau Peptides

Abstract

We studied fibril formation in a family of peptides based on PHF6 (VQIVYK), a short peptide segment found in the microtubule binding region of tau protein. N-Acetylated peptides AcVYK-amide (AcVYK), AcIVYKamide (AcPHF4), AcQIVYK-amide (AcPHF5), and AcV-QIVYK-amide (AcPHF6) rapidly formed straight filaments in the presence of 0.15 M NaCl, each composed of two laterally aligned protofilaments ϳ5 nm in width. X-ray fiber diffraction showed the omnipresent sharp 4.7-Å reflection indicating that the scattering objects are likely elongated along the hydrogen-bonding direction in a cross-␤ conformation, and Fourier transform IR suggested the peptide chains were in a parallel (AcVYK, AcPHF6) or antiparallel (AcPHF4, AcPHF5) ␤-sheet configuration. The dipeptide N-acetyl-YK-amide (AcYK) formed globular structures ϳ200 nm to 1 m in diameter. The polymerization rate, as measured by thioflavin S binding, increased with the length of the peptide going from AcYK 3 AcPHF6, and peptides that aggregated most rapidly displayed CD spectra consistent with ␤-sheet structure. There was a 3-fold decrease in rate when Val was substituted for Ile or Gln, nearly a 10-fold decrease when Ala was substituted for Tyr, and an increase in polymerization rate when Glu was substituted for Lys. Twisted filaments, composed of four laterally aligned protofilaments (9 -19 nm width, ϳ90 nm halfperiodicity), were formed by mixing AcPHF6 with AcVYK. Taken together these results suggest that the core of PHF6 is localized at VYK, and the interaction between small amphiphilic segments of tau may initiate nucleation and lead to filaments displaying paired helical filament morphology.

The Core of Tau-Paired Helical Filaments Studied by Scanning Transmission Electron Microscopy and Limited Proteolysis

“…The arrangement of tau in PHFs is unknown, but the data presented here and previously (2,15,31,56) provide some important constraints for possible models. The constraints include the following features:…”

Tau-Derived-Hexapeptide 306VQIVYK311 Aggregation Inhibitors: Nitrocatechol Moiety as A Pharmacophore In Drug Design

“…In agreement with a previous work, AcPHF6 in water displayed far-UV CD spectra with an intense negative minimum at ∼195 nm and a weak negative shoulder at ∼220 nm, which exhibits a dominantly disordered structure. 31 In the presence of MOPS buffer (5 mM MOPS, 150 mM NaCl, pH 7.2), AcPHF6 polymerized rapidly and formed a β-sheet structure, characterized by the negative maximum ellipticity at ∼218 nm and a positive maximum at ∼195 nm. This β-sheet structure was stable when monitored over a period of 24 h. The effect of test compounds on the β-sheet structure of AcPHF6, was investigated by recording the far-UV CD spectra of the hexapeptide in the presence of test compounds at t = 0, 2, and 24 h, respectively.…”

Interplay between I308 and Y310 residues in the third repeat of microtubule‐binding domain is essential for tau filament formation

“…This packing mode can easily interpret why the wild-type 4RMBD, and the Q307Y/Y310A and Q307Y mutants of 4RMBD exhibit prominent self-aggregation ability. In addition to the intramolecular C-H-p interaction, a p-p stacking interaction considered to be significant for the self-assembly of fibrils [7,8] is induced between neighboring Tyr residues. Although the mechanism of tau PHF formation has not yet been satisfactorily elucidated, the present work provides important information on the key residue and structural scaffold essential for forming a dry ''steric zipper" structure in tau amyloid fibrils.…”