orals 5th Asia-Pacific NMR Symposium 2013

The Influence of Local Interactions on the Fibrillation-Kinetics, Structure, and Dynamics of Amyloid β Peptides (#17)

Juliane Adler 1 , Holger A. Scheidt 1 , Daniel Huster 1
  1. Institute for Medical Physics and Biophysics, Leipzig University, Leipzig, Germany

The protein folding pathway to the highly ordered and biologically active form is determined by intramolecular interactions and the individual 3D structure of a given protein is encoded in the amino acid sequence. In addition another thermodynamically stable conformation can be formed, e.g. during pathological processes, which results in the formation of amyloid fibrils. Here, intermolecular interactions between the polymer chains dominate the formation of the cross-beta structure. More evidence accumulates that amyloid structures represents a common motif of proteins irrespective of their amino acid sequence. One underlying question for understanding the fundamental physical basics in this context is: How can local interactions influence the fibril forming kinetics, structure and dynamics? We study this question in model fibrils of Aβ(1-40), where amino acid mutations introduce local physical forces. We investigate how flexibility, electric charges, the replacement of a strong hydrophobic contact with a salt bridge and the effect of an introduced electrostatic repulsion influence the amyloid fibrils. Investigations of the structure and dynamics were performed using solid-state NMR. In our Aβ(1-40) model peptides, four amino acids where 13C labeled as probes of local structure and dynamics. The isotropic chemical shifts of the Cα and Cβ of each amino acid depend strongly on the secondary structure. Therefore the 13C cross-polarization spectra indicated local secondary structure elements. For dynamical studies DIPSHIFT experiments were performed, in order to measure 1H-13C dipolar couplings and determine order parameters. For almost all investigated peptide mutations fibril formation was observed with somewhat altered kinetics. Only one peptide in which a hydrophobic contact was replaced by a salt bridge resulted in no fibrils at all. Although several local structure changes were observed, the overall cross-beta structure turned out to be rather robust. Also subtle dynamical differences were observed.