Comparative fibril formation of analogs corresponding to the (12-24) segment of the β-amyloid peptide.

The (1-42) β-amyloid peptide is a main component of the plaques found in the brain of patients suffering from the Alzheimer's disease. As the single substitution of Glu for Gln at position 22 of this peptide seems to be responsible for the manifestation of the more severe amyloidosis (Dutch-type), we decided to evaluate the aggregation characteristics of peptide analogs interchanging Glu and Gln residues at positions 22 and also 15 in the minor (12-24) (VHHQ(15)KLVFFAE(22)DV) fragment. The Q15Q22, E15E22, E15Q22 and the native Q15E22 were compared to the (1-42) β-amyloid peptide in terms of fibril or structured aggregates formation propensity. In contrast to a rather similar solubility data measured of all analogs, fluorescence and light scattering methods indicated that only Q15E22 and Q15Q22 displayed relevant fibril formation capacity. Conversely, E15E22 and E15Q22 were not capable of the formation of this type of structure thus suggesting a key role for the Q(15) residue in the unique aggregation characteristic of the β-amyloid peptide.