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15N relaxation study of the amyloid β‐peptide: structural propensities and persistence length

The dynamics of monomeric Alzheimer Aβ(1–40) in aqueous solution was studied using heteronuclear NMR experiments. 15N NMR relaxation rates of amide groups report on the dynamics in the peptide chain and make it possible to estimate structural propensities from temperature‐dependent relaxation data and chemical shifts change analysis. The persistence length of the polypeptide chain was determined using a model in which the influence of neighboring residue relaxation is assumed to decay exponentially as a function of distance. The persistence length of the Aβ(1–40) monomer was found to decrease from eight to three residues when temperature was increased from 3 to 18 °C. At 3 °C the peptide shows structural propensities that correlate well with the suggested secondary structure regions of the peptide to be present in the fibrils, and with the α‐helical structure in membrane‐mimicking systems. Our data leads to a structural model for the monomeric soluble β‐peptide with six different regions of secondary structure propensities. The peptide has two regions with β‐strand propensity (residues 16–24 and 31–40), two regions with high PII‐helix propensity (residues 1–4 and 11–15) and two unstructured regions with higher mobility (residues 5–10 and 25–30) connecting the structural elements. Copyright © 2006 John Wiley & Sons, Ltd.