Solution NMR Studies of the Aβ(1−40) and Aβ(1−42) Peptides Establish that the Met35 Oxidation State Affects the Mechanism of Amyloid Formation

Abstract

The pathogenesis of Alzheimer's disease is characterized by the aggregation and fibrillation of the 40-residue A beta(1-40) and 42-residue A beta(1-42) peptides into amyloid plaques. The structural changes associated with the conversion of monomeric A beta peptide building blocks into multimeric fibrillar beta-strand aggregates remain unknown. Recently, we established that oxidation of the methionine-35 side chain to the sulfoxide (Met35(red) --> Met35(ox)) significantly impedes the rate of aggregation and fibrillation of the A beta peptide. To explore this effect at greater resolution, we carefully compared the (1)H, (15)N, and (13)C NMR chemical shifts of four A beta peptides that had the Met35 reduced or oxidized (A beta(1-40)Met35(red), A beta(1-40)Met35(ox), A beta(1-42)Met35(red), and A beta(1-42)Met35(ox)). With the use of a special disaggregation protocol, the highly aggregation prone A beta peptides could be studied at higher, millimolar concentrations (as required by NMR) in aqueous solution at neutral pH, remaining largely monomeric at 5 degrees C as determined by sedimentation equilibrium studies. The NOE, amide-NH temperature coefficients, and chemical shift indices of the (1)H alpha, (13)C alpha, and (13)C beta established that the four peptides are largely random, extended chain structures, with the Met35(ox) reducing the propensity for beta-strand structure at two hydrophobic regions (Leu17-Ala21 and Ile31-Val36), and turn- or bendlike structures at Asp7-Glu11 and Phe20-Ser26. Additional NMR studies monitoring changes that occur during aging at 37 degrees C established that, along with a gradual loss of signal/noise, the Met35(ox) significantly hindered upfield chemical shift movements of the 2H NMR signals for the His6, His13, and His14 side chains. Taken together, the present NMR studies demonstrate that the Met35(red) --> Met35(ox) conversion prevents aggregation by reducing both hydrophobic and electrostatic association and that the A beta(1-40)Met35(red), A beta(1-40)Met35(ox), A beta(1-42)Met35(red), and A beta(1-42)Met35(ox) peptides may associate differently, through specific, sharp changes in structure during the initial stages of aggregation.

The Structures of the E22Δ Mutant-Type Amyloid-β Alloforms and the Impact of E22Δ Mutation on the Structures of the Wild-Type Amyloid-β Alloforms

“…In agreement with previous experimental and theoretical studies, 15,[17][18][19]43 we detect that the β-sheet abundance in the C-terminal region of the wild-type Aβ42 is larger than that in the structures of the wild-type Aβ40 peptide. Surprisingly, we find that this trend is different in the structures of the E22Δ mutant-type Aβ40 and Aβ42 alloforms; the β-sheet abundance is larger in the C-terminal region of the E22Δ mutant-type Aβ40 rather than in its wild-type form.…”

Discriminating early stage Aβ42 monomer structures using chirality-induced 2DIR spectroscopy in a simulation study

“…(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Recent evidence supports the view that, at the monomeric level, the ensemble of Aβ is a mixture of multiple, nearly isoenergenic conformational species, in agreement with the energy landscape view of protein dynamics proposed by Frauenfelder and coworkers (22).…”

Metal swap between Zn7-metallothionein-3 and amyloid-β–Cu protects against amyloid-β toxicity

“…Although high Aβ concentrations substantially reduce free Cu(II) toxicity, this effect just delays the ROS Electronic absorption and circular dichroism measurements. The stock solutions of Aβ were prepared as described 47 Tris-HCl, 100 mM, NaCl, pH 7.4.…”