The Infrared Spectra of Polypeptides in Various Conformations: Amide I and II Bands¹

Self-assembly in aqueous solution of a modified amyloid beta peptide fragment

“…The peaks at 1693 and 1628 cm -1 , in the amide I band, are associated with a β-sheet structure [16,17]. In particular, the strong amide I band at 1628 cm -1 in combination with the weaker amide I band at 1693 cm -1 obtained for the transmission FT-IR, suggests an antiparallel β-sheet conformation of the peptide chains [16][17][18].…”

“…The amyloid β peptide is important in Alzheimer's, a so-called amyloid disease and is cleaved in vivo from a larger precursor protein to form fragments with predominantly 40 or 42 residues [1][2][3]. We have focussed on sequence KLVFF, corresponding to Aβ (16)(17)(18)(19)(20). This core sequence of the amyloid β peptide is believed to be critical in aggregation of Aβ into fibrils, as reviewed elsewhere [1].…”

Transformation of amyloid β(1–40) oligomers into fibrils is characterized by a major change in secondary structure

“…In its native state, Ab is supposed to adopt an a-helix structure embedded in the membrane, just after APP cleavage by secretases [43]. Lately, a high resolution structure of Ab monomers in solution stabilized by a phage-display selected Affibody Ò protein showed a b-hairpin structure implicating two short b-strands (aa 17-23 and aa [30][31][32][33][34][35][36] in an antiparallel organization [40]. The mechanism leading to fibrils formation thus somehow implicates a structural transition, which has been much less investigated because of the transitory and heterogeneous nature of aggregation intermediates currently considered as key factors in AD development.…”

“…4a, b). The presence of both components is typical of an antiparallel arrangement of the b-strands [34][35][36] and is attributed to oligomers [20]. When the peptide is incubated longer until it turns into fibrils, the 1,695 cm -1 peak vanishes, meaning most likely that the peptide reorganizes its b-strands from an antiparallel to a parallel b-sheet (Fig.…”

“…The relative intensity ratio of the 1,695 and the 1,630 cm -1 peaks has been suggested to be proportional to the percentage of antiparallel arrangement of the strands in a b-sheet [34][35][36]. Whereas the 1,695/1,630 cm -1 intensity ratio describes the amount of oligomers during the time course of aggregation, Thioflavin T fluorescence was used to probe the formation of fibrils (Fig.…”