Studies of Polymorphism of Amyloid-β42 Peptide from Different Suppliers.

The aim of this study was to investigate the process of amyloidogenesis of amyloid-β (Aβ)42 peptide, by means of fluorescence spectroscopy, electron microscopy, X-ray diffraction, and mass spectrometry. It has been repeatedly reported in the literature that the process of fibril formation by Aβ42 peptide depends considerably not only upon the specific conditions (ionic conditions, pH, temperature, mixing, etc.), as well as the manufacturing route (synthetic or recombinant), but also on the methods of synthesis and purification. We have, for the first time, systematically analyzed samples of Aβ42 peptide supplied by five different companies (Anaspec, Invitrogen, Enzo, Sigma-Aldrich, and SynthAssist) and obtained evidence of significant variability, including lot to lot variations. All studied samples formed amyloid-like fibrils at pH3-6, and the fibrils contained cross-β structures. Samples from Anaspec, Invitrogen, and Enzo formed one particular type of amyloid-like fibrils, while the samples from Sigma-Aldrich and SynthAssist formed another distinct type of fibrils. The observed polymorphism emphasizes the capacity of the Aβ42 peptide to act as a prion agent with varying structural characteristics. The presented data have allowed us to propose a possible mechanism of formation of amyloid-like fibrils.