Clarifying the influence of core amino acid hydrophobicity, secondary structure propensity, and molecular volume on amyloid-β 16-22 self-assembly.
The self-assembly of amyloid peptides is influenced by hydrophobicity, charge, secondary structure propensity, and sterics. Previous experiments have shown that increasing hydrophobicity at the aromatic positions of the amyloid-β 16-22 fragment (Aβ(16-22)) without introducing steric restraints greatly increases the rate of self-assembly and thermodynamically stabilizes the resulting fibrils [Senguen et al., Mol. BioSyst., 2011, DOI: 10.1039/c0mb00080a]. Conversely, when increasing side chain hydrophobicity coincides with an increase in side chain volume, the increase in the rate of self-assembly is offset by a thermodynamic destabilization of the resulting amyloid fibrils when direct cross-strand side chain interactions occur. These findings indicate that steric effects also influence the self-assembly of amyloidogenic peptides. Herein, the aromatic Phe residues at positions 19, 20, and 19,20 of Aβ(16-22) have been systematically replaced by Val, Leu, Ile, or hexafluoroleucine (Hfl) and amyloid formation has been characterized. The Val variants, despite the high β-sheet propensity of Val, were thermodynamically destabilized (ΔΔG = +0.1-0.4 kcal mol(-1)) relative to the wild-type with the double mutant failing to self-assemble at the concentrations studied. Conversely, the Leu and Ile variants formed fibrils at enhanced rates relative to wild-type and exhibited similar, or in some cases enhanced thermodynamic stabilities relative to the wild-type (ΔΔG = 0-0.6 kcal mol(-1)). The more hydrophobic Hfl variants were greatly stabilized (ΔΔG = -0.3-2.1 kcal mol(-1)) relative to the wild-type. These data indicate that hydrophobicity and steric effects both influence peptide self-assembly processes, including nucleation and fibrillization rates and the thermodynamic stability of the resulting fibrils.
Department of Chemistry, University of Rochester, Rochester, NY 14627-0216, USA.
F Timur
FT
Senguen
Todd M
TM
Doran
Elizabeth A
EA
Anderson
Bradley L
BL
Nilsson
D000596:Amino Acids / Q000737:chemistry*; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D006860:Hydrogen Bonding; D007700:Kinetics; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics
D000596:Amino Acids; D016229:Amyloid beta-Peptides