Steric Crowding of the Turn Region Alters the Tertiary Fold of Amyloid-β18-35 and Makes It Soluble.
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 Phe(19) and Leu(34) 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 Phe(19) and Leu(34) 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.
From the Department of Biochemistry, Seth G. S. Medical College and King Edward Memorial Hospital, Parel, Mumbai 400012, India.
Muralidharan
M
Chandrakesan
the Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India.
Debanjan
D
Bhowmik
the Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India.
Bidyut
B
Sarkar
the Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India.
Rajiv
R
Abhyankar
the Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India, and.
Harwinder
H
Singh
the Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India.
Mamata
M
Kallianpur
From the Department of Biochemistry, Seth G. S. Medical College and King Edward Memorial Hospital, Parel, Mumbai 400012, India.
Sucheta P
SP
Dandekar
the Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India, the Tata Institute of Fundamental Research Centre for Interdisciplinary Sciences, Narsinghi, Hyderabad 500 075, India madhu@tifr.res.in.
Perunthiruthy K
PK
Madhu
the Department of Chemical Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai 400005, India, maiti@tifr.res.in.
Sudipta
S
Maiti
the Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India, and venus.chem@gndu.ac.in.
Venus Singh
VS
Mithu
D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000235:genetics; D002942:Circular Dichroism; D007700:Kinetics; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013055:Spectrophotometry, Infrared
D016229:Amyloid beta-Peptides; C000607344:amyloid beta-protein (18-35), human
Alzheimer disease; amyloid; fluorescence correlation spectroscopy (FCS); nuclear magnetic resonance (NMR); protein aggregation; protein self-assembly; solid state NMR