Steric crowding of the turn region alters the tertiary fold of amyloid-β18–35and makes it soluble

Chandrakesan, Muralidharan ; Bhowmik, Debanjan ; Sarkar, Bidyut ; Abhyankar, Rajiv ; Singh, Harwinder ; Kallianpur, Mamata ; Dandekar, Sucheta P. ; Madhu, Perunthiruthy K. ; Maiti, Sudipta ; Mithu, Venus Singh (2015) Steric crowding of the turn region alters the tertiary fold of amyloid-β18–35and makes it soluble Journal of Biological Chemistry, 290 (50). pp. 30099-30107. ISSN 0021-9258

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Aβ self-assembles into parallel cross-β fibrillar aggregates, which is associated with Alzheimer's disease pathology. A central hairpin turn around residues 23–29 is a defining characteristic of Aβ in its aggregated state. Major biophysical properties of Aβ, including this turn, remain unaltered in the central fragment Aβ18–35. Here, we synthesize a single deletion mutant, ΔG25, with the aim of sterically hindering the hairpin turn in Aβ18–35. We find that the solubility of the peptide goes up by more than 20-fold. Although some oligomeric structures do form, solution state NMR spectroscopy shows that they have mostly random coil conformations. Fibrils ultimately form at a much higher concentration but have widths approximately twice that of Aβ18–35, suggesting an opening of the hairpin bend. Surprisingly, two-dimensional solid state NMR shows that the contact between Phe19 and Leu34 residues, observed in full-length Aβ and Aβ18–35, is still intact in these fibrils. This is possible if the monomers in the fibril are arranged in an antiparallel β-sheet conformation. Indeed, IR measurements, supported by tyrosine cross-linking experiments, provide a characteristic signature of the antiparallel β-sheet. We conclude that the self-assembly of Aβ is critically dependent on the hairpin turn and on the contact between the Phe19 and Leu34 regions, making them potentially sensitive targets for Alzheimer's therapeutics. Our results show the importance of specific conformations in an aggregation process thought to be primarily driven by nonspecific hydrophobic interactions.

Item Type:Article
Source:Copyright of this article belongs to American Society for Biochemistry and Molecular Biology.
Keywords:Alzheimer Disease; Amyloid; Fluorscence Correlation Spectroscopy (FCS); Nuclear Magnetic Resonance (NMR); Protein Aggregation; Protein Self-Assembly; Solid State NMR
ID Code:112949
Deposited On:24 May 2018 12:06
Last Modified:24 May 2018 12:06

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