Temperature-dependent β-sheet formation in β-amyloid Aβ1-40 peptide in water:: uncoupling β-structure folding from aggregation

To probe the role of temperature in the conversion of soluble Alzheimer's beta-amyloid peptide (A beta) to insoluble beta-sheet rich aggregates, we analyzed the solution conformation of A beta(1-40) from 0 to 98 degrees C by far-UV circular dichroism (CD) and native gel electrophoresis. The CD spectra of 15-300 mu g/ml A beta(1-40) in aqueous solution (pH similar to 4.6) at 0 degrees C are concentration-independent and suggest a substantially unfolded and/or unusually folded conformation characteristic of A beta monomer or dimer. Heating from 0 to 37 degrees C induces a rapid reversible coil to beta-strand transition that is independent of the peptide concentration and thus is not linked to oligomerization. Consequently, this transition may occur within the A beta(1-40) monomer or dimer. Incubation at 37 degrees C leads to slow reversible concentration-dependent beta-sheet accumulation; heating to 85 degrees C induces further beta-sheet folding and oligomerization. Our results demonstrate the importance of temperature and thermal history for the conformation of A beta. (C) 2000 Elsevier Science B.V. All rights reserved.