Fibrillization of 40-residue β-Amyloid Peptides in Membrane-Like Environments Leads to Different Fibril Structures and Reduced Molecular Polymorphisms

The molecular-level polymorphism in beta-Amyloid (A beta) fibrils have recently been considered as a pathologically relevant factor in Alzheimer's disease (AD). Studies showed that the structural deviations in human-brain-seeded A beta fibrils potentially correlated with the clinical histories of AD patients. For the 40-residue A beta (A beta(40)) fibrils derived from human brain tissues, a predominant molecular structure was proposed based on solid-state nuclear magnetic resonance (ssNMR) spectroscopy. However, previous studies have shown that the molecular structures of A beta(40)fibrils were sensitive to their growth conditions in aqueous environments. We show in this work that biological membranes and their phospholipid bilayer mimics serve as environmental factors to reduce the structural heterogeneity in A beta(40) fibrils. Fibrillization in the presence of membranes leads to fibril structures that are significantly different to the A beta(40) fibrils grown in aqueous solutions. Fibrils grown from multiple types of membranes, including the biological membranes extracted from the rats' synaptosomes, shared similar ssNMR spectral features. Our studies emphasize the biological relevance of membranes in A beta(40) fibril structures and fibrillization processes.