15N relaxation study of the amyloid beta-peptide: structural propensities and persistence length.

The dynamics of monomeric Alzheimer Abeta1-40 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 Abeta1-40 monomer was found to decrease from eight to three residues when temperature was increased from 3 to 18 degrees C. At 3 degrees 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 alpha-helical structure in membrane-mimicking systems. Our data leads to a structural model for the monomeric soluble beta-peptide with six different regions of secondary structure propensities. The peptide has two regions with beta-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.